Abstract:
The present invention relates to a method of identifying tree lineage capable of expressing desired biological and/or biochemical phenotypes and method of producing such trees. It also relates to a method of identifying a genetic marker associated with a genetic locus conferring at least one enhanced property. Also it relates to a stand of clonal enhanced property trees produced by the method of the present invention, the genome of the trees containing the same genetic marker associated with the enhanced property relative to a value characteristic of the average of the genus. It relates also to a method of producing a family of trees wherein at least about half exhibit at least of enhanced property. The present invention also relates to a genetic map of QTLs of trees associated with enhanced properties. The present invention further relates to a genetic marker of fiber length of trees.

Description:
[0001]    This application is a continuation-in-part of the application Ser. No. 09/494,501 filed on Jan. 31, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention is in the fields of tree improvement, forestry and pulp and paper evaluation technology. This invention allows for an enhanced selection efficiency for given trees from both natural and plantation populations with specific fiber and wood quality properties for value-added pulp and paper product lines.  
           [0004]    2. Description of Prior Art  
           [0005]    The utilization of species of the Populus genus of forest trees, particularly aspen and cottonwoods, as the cornerstone for the development of short-rotation intensive culture (SRIC) sustainable plantation forestry in the northern hemisphere has been promoted for a number of reasons, including greenhouse gas amelioration and phytoremediation. The primary driving force behind the implementation of SRIC Populus plantations, however, is their potential to alleviate the shortfall in world fiber supplies projected for 2010.  
           [0006]    This threat has provided an impetus for the examination of alternative fiber sources. Many non-wood sources have been characterized. “The morphology, ultrastructure and chemistry of wheat straw: a pulping perspective but the most logical and industrially expedient solution to the problem is likely to lie in fast-growing hardwood tree species. In the Southern hemisphere (and some parts of Europe), eucalyptus species are the hardwood of choice being prized for their growth rate, inherent adaptability and excellent papermaking properties.  
           [0007]    In the Northern hemisphere members of the genus Populus (including poplars and aspen) represent a similar opportunity having high growth rates—up to 30 m 3 /ha/yr in cold climates—producing pulps of high natural brightness and a wide range of fiber, pulping and pulp properties.  
           [0008]    Advantageously, poplars are unique in the additional potential they offer for genetic improvement of wood quality traits. Hybrid poplars are particularly well suited to genetic mapping studies as they are readily amenable to interspecies crosses, the progeny grow rapidly, and they have a relatively small genome. These advantages imply that the identification and manipulation of genetic control elements in poplars will be at least twice as easy as in rival fast-growing species such as eucalypts, and forty times easier than in radiata pine. Information generated by studies of this kind is extremely valuable for a number of reasons. Genetic control elements can be used to both rapidly and easily identify superior clonal material in natural populations and to screen such material for plantation establishment. Additionally, knowledge of the genetic structure of superior clones will open the door to transgenic manipulation to produce “ideal” trees (ideotypes) for specific end-product applications.  
           [0009]    In a previous study on a genetically well-characterized three-generation family of hybrid poplars ( Populus trichocarpa X  Populus deltoides —Family 331) developed by the University of Washington, this potential was assessed and exploited [PD4145]. Quantitative trait loci (QTL—genomic regions containing genes involved in the control of continuously variable traits*) for wood and fiber quality traits were determined. As an extension of, and complement to, this application, additional phenotypic information has been gathered for the same family grown at three separate sites. In this case, the industrially relevant traits examined were:  
           [0010]    fiber coarseness  
           [0011]    microfibril angle  
           [0012]    macerated fiber yield  
           [0013]    kraft pulp yield  
           [0014]    pulp properties including strength and air resistance  
           [0015]    kraft pulping H-factor  
           [0016]    specific refining energy  
           [0017]    lignin content  
           [0018]    wood extractive compounds content  
           [0019]    calcium salt accumulation  
           [0020]    The first four properties examined, fiber coarseness, microfibril angle, pulp yield and lignin content, are all critical pulp and papermaking parameters. The properties of a sheet of paper are dependent on the structural characteristics of the fibers which compose that sheet, the two most important characteristics being the length of the fibers and their coarseness (a weight to length measure). Length is required for strength properties, particularly so for hardwood species as longer-fiberd hardwood pulps can be used to reduce the expensive softwood component of certain papermaking furnishes. In softwoods, increasing fiber length can actually be problematic as excessively long fibers are prone to flocculation. Coarseness is often (but not always, c.f. red and sugar maple) a reasonable indicator of the thickness of the fiber cell wall. Wall thickness determines whether the fibers will collapse to readily form flat ribbons, giving paper sheets a smooth surface, or be less uncollapsible providing sheet bulk and absorbancy. Consequently, coarser, generally thicker-walled, fibers (e.g. Douglas fir) resist collapse and produce open, absorbent, bulky sheets with low burst/tensile strength and high tear strength.  
           [0021]    The structural framework of the cell wall of fibers is primarily provided by cellulose microfibrils in the thickest S2 layer, cemeted together with lignin. The lignin binds the microfibrils and prevents their lateral buckling under load. The parameter microfibril angle indicates the angle to the longitudinal axis of the fiber at which the microfibrils are wound around the cell in a spiral formation. The smaller the angle, the steeper the spiral (in general, microfibril angle is at its highest near the pith, decreases through the juvenile wood core and then reaches a stable level in the mature wood). Microfibril angle has a major effect on the physical strength of directed axially along the microfibril. The steeper the angle, the stronger the fiber and the higher the tensile modulus. In this capacity therefore, microfibril angle is a critical strength parameter for both pulp and paper and solid wood applications of forest species.  
           [0022]    Pulp yield is a measure of the amount of fiber recovered from an initial charge of wood. A great deal of chemical engineering effort is routinely expended to achieve process improvements in yield of the order of 0.5-1.0%. (e.g. polysulfide process). As wood quality databases become gradually more comprehensive, it is clear that both inter- and intra-species variability for this parameter can vastly outweigh such a change. Indeed, recent research has suggested that choosing one aspen (Populus tremuloides) clone over another of the same species for pulping can result in a yield improvement of 4-6% at a given kappa number. The efficiency of the pulping process, and a number of subsequent papermaking parameters, are critically dependent on the amount and chemical composition of the lignin polymer found in the wood. Normal softwood lignin is mainly composed of guaiacylpropane subunits which are difficult to remove via conventional processes. By contrast, hardwood lignin is composed of both guaiacyl- and syringylpropane units, in which the ratio of the two phenylpropanes varies between species.  
           [0023]    If the genetic control of the lignin biosynthetic pathway can be determined, it may be possible to assess softwood populations for clones with hardwood-like lignin or to produce more syringyl residues in softwood lignin. Transgenic manipulation is also possible and, indeed, several research groups are already manipulating some of the control enzymes of the lignin biosynthetic pathway with varying results.  
           [0024]    Specific extractives of wood are well known to cause adverse effects on various aspects of pulp and papermaking, specifically pitch deposition and effluent toxicity, particularly for mechanical pulping operations.  
           [0025]    It has been estimated that pitch deposition problems (such as dispersed wood resin, metal soaps, wood resin component polymerization and surface active agent foaming) cost the Canadian industry several hundred million dollars annually. These extractive effects in open systems are already disproportionate to their concentration (extractives comprise ˜1-5% of the weight of wood) and it is anticipated that the problems will be exacerbated by progress towards mill system closure. For species used in mechanical pulping, such as aspen and related species, there are additional problems with pulp brightening caused by high extractives content.  
           [0026]    A number of research groups have previously noted that certain poplar species have an inherent tendency to accumulate mineral deposits, particularly calcium salt crystals in their wood. Evidence described in these papers suggests that these crystals do not represent abnormalities but rather are consistently present in some Populus lineages (particularly the sections Aigeros and Tacamahaca). The crystals were found to accumulate in the stem, branches, roots and within vessels and fibers frequently occluding them completely. This paper reports the confirmation of these findings using the well-characterized hybrid poplar family and documents the effects of these crystals on the pulp properties of the hybrid family.  
           [0027]    It would be highly desirable to be provided with a nucleic acid-based marker for tree phenotype prediction and method thereof.  
         SUMMARY OF THE INVENTION  
         [0028]    The aim of the present invention is to provide a method for identifying individual trees having a superior phenotype.  
           [0029]    A number of previous studies [Bradshaw, H. D., Villar, M., Watson, B. D., Otto, K. G., and Stewart, S. “Molecular genetics of growth and development in Populus III. A genetic linkage map of a hybrid poplar composed of RFLP, STS and RAPD markers,” Theor. Appl. Genet. 89, 551-558 (1994)] have suggested that growth, adaptive and wood quality traits are not controlled by huge numbers of genes with small effects but that they are determined by a few genes with large effects whose influences are tempered by environmental blurring. The method described in this application demonstrates that this situation also holds for fiber and wood quality property determinants. For each trait examined in the application (except certain kraft and APRMP pulping properties), QTL have been found which contribute significantly to the phenotypic variance observed for that trait.  
           [0030]    Of greatest significance are certain QTL which have proven to be coincident in their location on the genetic map. The QTL for tensile index and air resistance are in the same genetic location and critically they also overlap the QTL for fiber coarseness and microfibril angle. This adds compelling evidence to the hypothesis that there is a causal relationship between these fiber properties and certain pulping characteristics and that rapid assessment of the former may potentially be an indicator of the latter. Equally significantly, other QTL are not coincident for example, those detected for lignin content, H-factor and pulp yield. The fact that these properties do not appear to be controlled by the same set of genes emphasizes the complexity of the determination of H-factor and yield properties and further indicates that simple alteration of lignin content may not be the key to reliable manipulation of pulping characteristics of trees.  
           [0031]    These QTL can be used for the development of marker-assisted breeding or rapid assessment techniques (based on assays or microarray technologies) which could save the pulp and paper industry much time and money in the refinement and development of new and better products based on purpose-grown fiber of known quality. The QTL can be applied to enhance and direct tree-breeding experiments to the improvement of wood quality traits and to the rapid assessment of natural stands on the basis of their fiber and wood quality properties.  
           [0032]    In accordance with the present invention there is provided a method of identifying tree lineage capable of expressing desired biological and/or biochemical phenotypes comprising the steps of:  
           [0033]    a) obtaining a nucleic acid sample from the trees of pure species and/or hybrids thereof;  
           [0034]    b) obtaining either a restriction pattern (RFLP) or PCR-fingerprint by subjecting the nucleic acid of step (a) to at least one restriction enzyme and/or standard PCR conditions with at least one specific primer;  
           [0035]    c) correlating the PCR-fingerprint or restriction pattern of step (b) to at least one selected biological and/or biochemical phenotype of the tree wherein the phenotype is associated with a genetic locus identified by and/or associated with the PCR fingerprint or restriction pattern.  
           [0036]    The method in accordance with a preferred embodiment of the present invention, wherein the PCR-fingerprint is selected from the group consisting of RAPD, AFLP, CAP and SCAR.  
           [0037]    The method in accordance with a preferred embodiment of the present invention, wherein the correlating of step (c) further comprises the sequencing of polymorphic DNA products associated with the genetic locus associated with the phenotype.  
           [0038]    The method in accordance with a preferred embodiment of the present invention, wherein DNA sequences represent candidate genes or are highly linked to candidate genes for use as DNA markers as in step (c).  
           [0039]    The method in accordance with a preferred embodiment of the present invention, wherein the DNA sequences are physically and/or genetically linked to candidate genes.  
           [0040]    The method in accordance with a preferred embodiment of the present invention, wherein the tree of pure species and/or hybrid thereof is naturally or artificially produced.  
           [0041]    The method in accordance with a preferred embodiment of the present invention, wherein the sample of step (a) is obtained from a leaf, cambium, root, bud, stem, cork, phloem, flower, seed, seeds pods or xylem.  
           [0042]    The method in accordance with a preferred embodiment of the present invention, wherein the tree is of the genus selected from the group consisting of: Populus, Picea, Betula, Abies, Larix, Taxus, Ulmus, Prunus, Quercus, Malus, Arbutus, Salix, Platanus, Acer, Tsuga, Pseudotsuga, Pinus, Fraxinus, Eucalyptus, Acacia, Abrus, Cupressus, Fagus, Juniperus, Thuja and Canya.  
           [0043]    In accordance with the present invention, there is provided a method of identifying a genetic marker associated with a genetic locus conferring at least one enhanced property selected from the group consisting of fiber length, fiber coarseness, DBII (diameter at breast height), microfibril angle, density, pulp strength, pulp yield, lignin content, pitch propensity and calcium accumulation in a family of trees, which comprises the steps of:  
           [0044]    a) obtaining a sexually mature parent tree exhibiting enhanced properties;  
           [0045]    b) obtaining a plurality of progeny trees of the parent tree by performing self or cross-pollination;  
           [0046]    c) assessing multiple progeny trees for each of a plurality of genetic markers;  
           [0047]    d) identifying genetic markers segregating in an essentially Mendelian ratio and showing linkage with at least some other of the plurality of genetic markers;  
           [0048]    e) measuring at least one of the properties in multiple progeny trees; and  
           [0049]    f) correlating the presence of enhanced property with a least one marker identified in step d) as segregating in an essentially Mendelian ratio and showing linkage with at least some of the other markers, the correlation of the presence of enhanced properties with a marker indicating that the marker is associated with a genetic locus conferring enhanced; wherein the family of trees comprises a parent tree and its progeny.  
           [0050]    The method in accordance with a preferred embodiment of the present invention, further comprising constructing a genetic linkage map of the parent tree using the plurality of genetic markers.  
           [0051]    The method in accordance with a preferred embodiment of the present invention, wherein the genetic linkage map is a QTL map.  
           [0052]    The method in accordance with a preferred embodiment of the present invention, wherein the genetic marker loci are restriction fragment length polymorphism (RFLPs) or PCR-fingerprint.  
           [0053]    The method in accordance with a preferred embodiment of the present invention, wherein the restriction fragment length polymorphism (RFLPs) or PCR-fingerprint are correlated with a locus or with a quantitative traits loci (QTLs).  
           [0054]    The method in accordance with a preferred embodiment of the present invention, wherein the parent tree is the seed parent tree to each of the progeny trees, root, leaf or cambium tissue from the progeny trees is assessed for the presence or absence of genetic markers in step c).  
           [0055]    The method in accordance with a preferred embodiment of the present invention, wherein the parent tree is a species of  Populus trichocarpa, Populus deltoides, Populus tremuloides  or a hybrid thereof.  
           [0056]    In accordance the present invention, there is provided a method of producing a plurality of clonal trees that have at least one enhanced property selected from the group consisting of fiber length, fiber coarseness, DBII (diameter at breast height), microfibril angle, density, pulp strength, pulp yield, lignin content, pitch propensity and calcium accumulation, which comprises the steps of:  
           [0057]    a) obtaining a sexually mature parent tree exhibiting enhanced property relative to a value characteristic of the average of the genus;  
           [0058]    b) obtaining a plurality of progeny trees of the parent tree by performing self or cross-pollination;  
           [0059]    c) assessing multiple progeny tress for each of a plurality of genetic markers;  
           [0060]    d) identifying genetic markers segregating in an essentially Mendelian ratio and showing linkage with at least some other of the plurality of genetic markers;  
           [0061]    e) measuring at least one of the properties in multiple progeny trees;  
           [0062]    f) correlating the presence of enhanced property with a least one marker identified in step d) as segregating in an essentially Mendelian ratio and showing linkage with at least some of the other markers;  
           [0063]    g) selecting a progeny tree containing a marker identified in step f) as associated with a genetic locus conferring enhanced property; and  
           [0064]    h) vegetatively propagating the progeny tree selected in step g) to produce a plurality of clonal trees, essentially all of the clonal trees exhibiting enhanced fiber length.  
           [0065]    In accordance with the present invention, there is provided a stand of clonal enhanced property trees produced by the method of the present invention, the genome of the trees containing the same genetic marker associated with the enhanced property relative to a value characteristic of the average of the genus.  
           [0066]    In accordance with the present invention, there is provided a method of producing a family of trees wherein at least about half exhibit at least of enhanced property selected from the group consisting of fiber length, fiber coarseness, DBII (diameter at breast height), microfibril angle, density, pulp strength, pulp yield, lignin content, pitch propensity and calcium accumulation, which comprises the steps of:  
           [0067]    a) obtaining a sexually mature parent tree exhibiting enhanced property relative to a value characteristic of the average of the genus;  
           [0068]    b) obtaining a plurality of progeny trees of the parent tree by performing self or cross-pollination;  
           [0069]    c) assessing multiple progeny tress for each of a plurality of genetic markers;  
           [0070]    d) identifying genetic markers segregating in an essentially Mendelian ratio and showing linkage with at least some other of the plurality of genetic markers;  
           [0071]    e) measuring at least one of the properties in multiple progeny trees;  
           [0072]    f) correlating the presence of enhanced fiber length with a least one marker identified in step d) as segregating in an essentially Mendelian ratio and showing linkage with at least some of the other markers;  
           [0073]    g) selecting a progeny tree containing a marker identified in step f) as associated with a genetic locus conferring enhanced property; and  
           [0074]    h) sexually propagating the progeny tree selected in step g) to produce a family of trees, at least about half of the family of trees containing a genetic locus conferring enhanced property and the family of trees exhibiting enhanced property.  
           [0075]    In accordance with the present invention, there is provided a genetic map of QTLs of trees associated with enhanced properties as set forth in FIG. 30.  
           [0076]    The genetic map in accordance with a preferred embodiment of the present invention, wherein the enhanced properties are selected from the group consisting of fiber length, fiber coarseness, DBII (diameter at breast height), microfibril angle, density, pulp strength, pulp yield, lignin content, pitch propensity and calcium accumulation.  
           [0077]    In accordance with the present invention, there is provided a genetic marker of fiber length of trees, which comprises a 800 bp amplification product, wherein presence of the product in an amplified DNA sample from the trees is indicative of a short fiber length&lt;0.92 mm and absence of the product is indicative of long fiber length&gt;0.92 mm.  
           [0078]    For the purpose of the present invention the following terms are defined below.  
           [0079]    The term “Quantitative Trait locus (QTL)” is intended to mean the position(s) occupied on the chromosome by the gene(s) representing a particular trait. The various alternate forms of the gene—that is the alleles used in mapping—all reside at the same location.  
           [0080]    The term “restriction fragment linked polymorphism (RFLP)” as used herein means a digestive enzymatic method for detecting localized differences in DNA sequence.  
           [0081]    The term “random amplified polymorphic DNA (RAPD)” as used herein means a PCR based method for detecting localised differences in DNA sequence.  
           [0082]    The term “polymerase chain reaction (PCR)” as used herein means a cyclical enzyme-mediated method for making large numbers of identical copies of a stretch of DNA using specific primers.  
           [0083]    The term “hybrid thereof” as used herein means a progeny issued from the interbreeding of trees of different breeds, varieties or species especially as produced through tree-breeding for specific genetic and phenotypic characteristics. A hybrid thereof is derived by cross-breeding two different tree species.  
           [0084]    The term “candidate gene” as used herein means a sequence of DNA representing a potential gene (an open reading frame, ORF) located within a QTL whose predicted functionality may partially or totally be causal to the given phenotypic trait associated with the QTL.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0085]    [0085]FIG. 1 illustrates SilviScan-2 analysis of hybrid poplar core 331-1062. Data indicate the expected increase in MFA from bark (mature wood zone) to pith (juvenile wood zone). Three scans were performed at resolutions of 1 mm, 2 mm and 5 mm.  
         [0086]    [0086]FIG. 2A illustrates GC spectrum for acetone extractives from  Populus tremuloides  (quacking aspen);  
         [0087]    [0087]FIG. 2B illustrates GC spectrum for hybrid poplar 331-1016 (F2 TD×TD cross);  
         [0088]    [0088]FIG. 3 illustrates accept chips % vs. wood density for selected clones which is indicating no correlation;  
         [0089]    [0089]FIG. 4 illustrates bulk density vs. chip density for hybrid poplar chips showing the expected strong correlation  
         [0090]    [0090]FIG. 5 illustrates Kappa number vs. H-factor: clone 331-1136 which proved difficult to pulp is clearly distinct from the others;  
         [0091]    [0091]FIG. 6 illustrates pulp yield vs. kappa number;  
         [0092]    [0092]FIG. 7 illustrates Yield at kappa 17 vs. H-factor to kappa 17;  
         [0093]    [0093]FIG. 8 illustrates chip density vs. H-factor to kappa 17;  
         [0094]    [0094]FIG. 9 illustrates fiber coarseness vs. fiber length;  
         [0095]    [0095]FIG. 10 illustrates chip density vs. fiber length;  
         [0096]    [0096]FIG. 11 illustrates tensile index vs. bulk;  
         [0097]    [0097]FIG. 12 illustrates histogram of tensile strength and bulk properties for the examined genotypes;  
         [0098]    [0098]FIG. 13 illustrates tensile index development by PFI beating;  
         [0099]    [0099]FIG. 14 illustrates tensile index vs. Canadian standard freeness;  
         [0100]    [0100]FIG. 15 illustrates air resistance (Gurley) vs. sheet density;  
         [0101]    [0101]FIG. 16 illustrates sheet density vs. Sheffield smoothness;  
         [0102]    [0102]FIG. 17 illustrates scattering coefficient vs. Canadian standard freeness shows very poor correlation;  
         [0103]    [0103]FIG. 18 illustrates handsheet deformations caused by calcium deposition;  
         [0104]    [0104]FIG. 19 illustrates EDS characterization of vessel element mineral deposits;  
         [0105]    [0105]FIG. 20 illustrates Electron micrograph of vessel element mineral deposition;  
         [0106]    [0106]FIG. 21 illustrates unscreened Canadian standard freeness vs. specific refining energy exhibits low, medium and high refining energy demand envelopes at a given freeness value;  
         [0107]    [0107]FIG. 22 illustrates uptake of NaOH and H 2 O 2  vs. specific refining energy;  
         [0108]    [0108]FIG. 23 illustrates mean chemical uptake vs. chip density;  
         [0109]    [0109]FIG. 24 illustrates mean chemical uptake vs. tensile index at 200 mL;  
         [0110]    [0110]FIG. 25 illustrates uptake vs. wood chip density;  
         [0111]    [0111]FIG. 26 illustrates fines content vs. scattering coefficient indicating high levels of intraclonal variability;  
         [0112]    [0112]FIG. 27 illustrates mean chemical uptake vs. scattering coefficient;  
         [0113]    [0113]FIG. 28 illustrates roughness vs. freeness;  
         [0114]    [0114]FIG. 29 illustrates Sheffield smoothness vs. tensile index; and  
         [0115]    [0115]FIG. 30 illustrates genetic map of the hybrid poplar population produced using Mapmaker 3.0 and Mapmaker/QTL 1.1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0116]    In accordance with the present invention, there is provided nucleic acid-based marker for tree phenotype prediction and method thereof.  
         [0117]    Materials and Methods  
         [0118]    Sample Sites  
         [0119]    Sampling was conducted at the Washington State University Farm plantation site in Puyallup, Washington and at two commercial plantation sites in Northern Oregon at Clatskanie and Boardman. The pedigree sampled was founded in 1981 by interspecific hybridization between Populus trichocarpa (clone 93-968) and  P. deltoides  (clone ILL-129). Two siblings from the first hybrid generation (F1 family 53), 53-246 and 53-242, were crossed in 1988 to give rise to a family of second generation hybrids used for genetic mapping studies (F2 family 331). Unrooted cuttings of the P, F1 and 55 F2 clones were planted at the sites in a modified randomized complete block design at a 2×2 m spacing. At the time of sampling, the trees were seven (Puyallup) and five (Clatskanie, Boardman) years old.  
         [0120]    Tree Sampling  
         [0121]    Ten millimeters diameter increment cores were obtained at approximately breast height from 350 surviving trees (90 genotypes) within the pedigree. All cores were removed through the pith from bark to bark. For pilot Kraft pulping analyses, 25 stems were selected—based on the fiber properties and wood density phenotypic data—and harvested from the Puyallup site. The entire stem to a 1″ top size was recovered in each case. Genotyping experiments were performed on DNA extracted from 30 g of live tissue (leaf samples) obtained from each of the 90 sampled genotypes spanning the three growth sites.  
         [0122]    Fiber Coarseness and Macerated Pulp Yield  
         [0123]    Fibers for analysis were obtained from hand-chipped 10 mm increment cores using an acetic acid/hydrogen peroxide maceration technique whereby a known oven-dried (o.d.) weight of chips was first placed in a test tube, saturated with water then covered in maceration solution [1:1 mixture of glacial acetic acid: hydrogen peroxide (30% from stock bottle)]. These samples were then incubated in a dry heating block for 48 hrs at 60° C. The maceration solution was washed from the chips extensively using distilled water and the pulps disintegrated in a small Hamilton Beach mixer. A dilution series was then used to obtain representative samples of 10,000-20,000 fibers (corresponding to approximately 5 mg of macerated pulp) which were analyzed for length and coarseness values using a Kajaani FS-200 instrument and/or an OpTest Fiber Quality Analyzer. Maceration yields were calculated from oven-dried recovered pulps after fiber analysis.  
         [0124]    Microfibril Angle  
         [0125]    Microfibril angle (MFA) was measured on 45 whole increment core samples from the family 331 hybrid poplars. The cores were selected on the basis of sufficient size (&gt;20 mm) and soundness of the wood. Prior to analysis, the cores were extracted in denatured ethanol for three days and dried. MFA was determined by SilviScan-2 analysis using scanning X-ray diffractometry [Evans, R. a variance approach to the X-ray diffractometric estimation of microfibril angle in wood. appita J. 52(4), 283-289 (1999)]. Acquisition time was set for 30 seconds to optimize signal to noise ratio and a single diffraction pattern was obtained for each sample to ensure that the entire length of the sample was represented. MFA was estimated from the standard deviation (S) of the 002 azimuthal diffraction profile where:  
         MFA=1.28(S 2 -36) 1/2    
         [0126]    S and MFA are both measured in degrees.  
         [0127]    Chemical Analyses—Lignin, Extractives (GCIMS)  
         [0128]    1. Lignin  
         [0129]    Lignin contents were determined for 90 genotypes sampled at the Puyallup growth site. The determinations were performed at the Paprican Pointe Claire facility according to TAPPI standard methods (T13 wd 74).  
         [0130]    2. Extractives Preparation  
         [0131]    The samples were ground in a Wiley Mill at 40 mesh and a 5-6 g o.d. aliquot of the ground wood was placed in a soxhlet thimble and continuously extracted with acetone for 6 hours. The resulting filtrate was concentrated by rotary evaporation and filtered through a pasteur pipette with glass wool, in order to remove any large particulates. The filtrate was then freeze dried, accurately weighed and the resulting crystals re-suspended in acetone to give a concentration of 5,000 ppm based on the total extractives yield. The internal standards, cholesterol palmitate and heptadeptanoic acid (C-17), were added to every one of the extracted samples, at a concentration of 200 ppm. The samples were then transferred to GC vials for analysis of fatty acids by GCMS, using a 10 m DB-XLB column (J&amp;W). The set temperature program started out at 50° C. for 3 minutes, before ramping the temperature up to 340° C. at a rate of 10° C. per minute. This was then followed by maintaining the temperature at 340° C. for 30 minutes and again ramping up to 360° C. at a rate of 10° C. per minute. The injector temperature was held at 320° C. and a constant flow rate of 1.6 mL/minute was maintained. A solvent delay of 5 minutes was set up and data acquisition began at that point. In order for ion detection to occur, a compound table of known retention times was built. Peaks were detected by quantions (RIC) and integrated. Area ratios were determined relative to the internal standard, cholesterol palmitate.  
         [0132]    The peaks were identified and integrated via the compound table that was constructed as a part of the MS data calculations [Fernandez, MP, Watson, PA, Breuil, C. Gas Chromatography-mass extractive compounds in quaking aspen. Journal of Chromatography A, 922(ER1-2): 225-233 (2001). The resulting area integrations from each spectrum were divided into the internal standard, cholesterol palmitate, to give a ratio. This relative number was then used on a peak specific basis (peak identification by retention time) as phenotypic data for genetic mapping experiments. The area of particular interest falls between 25 to 40 minutes and contains the waxes, sterols and steryl esters, the major components of pitch in wood.  
         [0133]    Pulps Preparation  
         [0134]    1. Wood Chip Preparation  
         [0135]    Selected wood logs from the 25 hybrid poplar clones from the base up to a 1″ top diameter were debarked, slabbed (if necessary to reduce the diameter) on a portable Woodmizer LT-15 sawmill and chipped using a 36″ CM&amp;E 10-knife industrial disc chipper. A portion of the chips were air-dried and later screened in a Wennberg chip classifier to obtain chips in the thickness range of 2-6 mm for chemical pulping. These accept chips were used in the kraft cooks. The remaining green chips were screened on a BM&amp;H vibratory screen to remove over sized chips and fines prior to mechanical pulping.  
         [0136]    2. Kraft Pulping  
         [0137]    Three representative aliquots of air-dried accept chips from each of the samples were kraft pulped in bombs [45 g oven-dried (o.d.) charge] within a B-K micro-digester assembly. The cooking conditions were as follows:  
         [0138]    Time to maximum temperature: 135 min  
         [0139]    Maximum cooking temperature: 170° C.  
         [0140]    Effective alkali, % OD weight of wood: 13%  
         [0141]    % Sulphidity: 25%  
         [0142]    Liquor to wood ratio: 5:1  
         [0143]    H factor: 700-1400  
         [0144]    All of the pulps produced were washed, oven-dried and weighed to determine pulp yield. Kappa number and black liquor residual effective alkali were determined by TAPPI standard procedures (T236 cm 85 and T625 respectively). From these results the optimum cooking conditions required to produce pulps at 17 Kappa number were estimated by fitting regression lines through each set of data (r 2 ≧0.95). Large quantities of kraft pulp were subsequently produced in a 28 L Weverk laboratory digester. The pulps produced were disintegrated, washed and screened through an 8-cut screen plate.  
         [0145]    A PFI mill was used to prepare 5-point beating curves for each pulp sample by refining at: 0, 1000, 3000, 6000 revolutions (CPPA Standard C.7). A disintegrator (CPPA Standard C.9P) and a stainless steel sheet machine were used for testing and forming all sets of handsheets (CPPA Standard C.4 and C.5). All physical and optical testing was performed in a constant temperature and humidity room, using CPPA standard methods.  
         [0146]    3. Alkaline Peroxide Refiner Mechanical Pulping (APRMP)  
         [0147]    Two-stage impregnation of twenty-four hybrid poplar chips samples was carried out using a Sunds Defibrator Prex impregnator with a 3:1 compression ratio.  
         [0148]    Stage One  
         [0149]    Chips were steamed at atmospheric pressure for 10 min to expel entrapped air from the chips and replace it with water vapour. Impregnation with a solution containing 0.25% DTPA (diethylenetriamine pentaacetic acid) was carried out in the Prex impregnator. This provided a chemical charge of 0.26% to 0.66% DTPA on o.d. wood.  
         [0150]    Stage Two  
         [0151]    First-stage impregnated chips were further impregnated with a solution containing 0.25% MgSO 4 , 2.0% Na 2 SiO 3 , 2.35% NaOH and 1.5% H 2 O 2 . This resulted in chemical charges as follows:  
                                                       MgSO 4  applied, % o.d. wood:   0.36 to 0.69           Na 2 SiO 3  applied, % o.d. wood:   2.29 to 5.45           NaOH applied, % o.d. wood:   3.69 to 5.89           H 2 O 2  applied, % o.d. wood:   1.72 to 3.76                      
 
         [0152]    After 60 min retention at 60° C. the side port of the preheater was opened to remove the impregnated chips for open-discharge refining in a 30.5 cm single-disc Sprout Waldron laboratory refiner to prepare alkaline peroxide refiner mechanical pulps (APRMP). Each chip sample was refined at three energy levels to give 72 APRMP pulps in the freeness range from 144 to 402 mL Csf. Immediately after first pass open-discharge refining the pulp stock was neutralized to pH 4.5-4.8. Wood chip density and chemical uptake of hybrid poplar chip samples are shown in Table XIX.  
         [0153]    Other pertinent refining conditions are shown below:  
                                                       Plates   D2A507           Number of passes   2 to 4 depending upon freeness level           Nominal plate gap   0.38 mm (first pass)               0.03 to 0.2 mm (subsequent passes)           Refining consistency   18 to 23% o.d. pulp                      
 
         [0154]    After latency removal, each pulp was screened on a 6-cut laboratory flat screen to determine screen rejects. Bauer-McNett fiber classifications on screened pulps were determined. Representative samples from each of the 72 pulp samples were analyzed for fiber length using a Kajaani FS-200 instrument. Handsheets were prepared with white water recirculation to minimize the loss of fines and tested for bulk, mechanical, and optical properties using CPPA standard methods. Handsheet roughness was measured in Sheffield units (SU).  
         [0155]    Assessment of Calcium Accumulation  
         [0156]    The nature of the observed kraft pulp handsheet deformations was explored by both light and electron microscopy and by energy-dispersive X-ray analysis. Wood chip deposits were characterized in similar fashion. The methodologies used have been described fully in a previous report.  
         [0157]    Genetic Map Construction and QTL Mapping  
         [0158]    The Populus genetic map used in this application, previously constructed using the same family 331 pedigree, consists of 342 RFLP, STS and RAPD markers and is described in [Bradshaw, H. D., Villar, M., Watson, B. D., Otto, K. G., and Stewart, S. “Molecular genetics of growth and development in Populus III. A genetic linkage map of a hybrid poplar composed of RFLP, STS and RAPD markers,” Theor. Appl. Genet. 89, 551-558 (1994)]. The 19 large linkage groups, corresponding closely to the 19 Populus chromosomes, were scanned for the phenotypic data obtained using the program MAPMAKER-QTL 1.1. Based on the scanned genome length and the distance between genetic markers, a logarithmic odds (LOD) significance threshold level of 2.9 was chosen (this ensures that the chance of a false positive QTL being detected is at most 5%). For more details on the QTL mapping procedure employed.  
         [0159]    RAPD Analysis, Polymerase Chain Reaction (PCR) and Product Cloning  
         [0160]    For each trait examined, QTL-associated markers were identified from the genetic map and were employed to generate polymorphic products from phenotyptically selected F2 generation individuals. Random Amplified Polymorphic DNA (RAPD) markers were purchased from Operon Technologies Inc. (Alameda, Calif., U.S.A.) and Restriction Fragment Linked Polymorphism (RFLP) markers were constructed from published sequence data by the Biotechnology Laboratory at the University of British Columbia.  
         [0161]    Both types of markers were used in standard PCR reactions to generate polymorphic amplified product bands corresponding to the QTL-linked markers identified on the genetic map. PCR conditions were standard for RAPD analyses (H. D. Bradshaw, personal communication) and performed using rTaq polymerase (Amersham-Pharmacia) and a Techne Genius thermal cycler. Cycle conditions were as follows:  
         [0162]    step  
         [0163]    1: 94° C., 3 min  
         [0164]    2: 94° C., 5 sec  
         [0165]    3: 36° C., 30 sec  
         [0166]    4: 72° C., 1 min  
         [0167]    5: Repeat 2-4, 34× 
         [0168]    6: 4° C., hold  
         [0169]    PCR products from the phenotypically selected F2 generation individuals were separated on 1% agarose gels according to standard methods and polymorphic bands of the appropriate size were excised from the gels. Products were purified from the agarose using the Amersham-Pharmacia GFX PCR gel band purification kit and cloned into the Promega pGEM-T vector system (with supplied competent cells) according to manufacturers&#39; protocols and standard blue/white selection cloning procedures on ampicillin agar. Cloned PCR products were prepared from transformed cells using the Promega Wizard Plus miniprep kit, again according to the manufacturers protocols, and were then sequenced at the Biotechnology Laboratory, University of British Columbia.  
         [0170]    Results and Discussion  
         [0171]    Fiber Coarseness and Macerated Pulp Yield  
         [0172]    Fiber length and coarseness and macerated pulp yield data were obtained on core samples for each of the 350 trees sampled in the study using the pulp maceration technique and either the Kajaani FS-200 or the automated OpTest FQA instruments and are presented in Table I.  
                                                           TABLE 1                           Fiber length, coarseness and macerated pulp yield data            Clone ID   Yield   Fiber Length   Coarseness   Site                     14-129   46.2   0.84   0.065   Puyallup        14-129   44.1   0.76   0.085        93-968   50.8   0.99   0.095        93-968   49.9   0.97   0.112        93-968   50.5   0.98   0.102        53-242   50.9   0.85   0.082        53-242   47   0.83   0.069        53-242   52.4   0.79   0.076        53-246   50.9   0.83   0.065        53-246   46.8   0.84   0.082       331-1059   55.9   0.83   0.083       331-1059   47.6   0.74   0.075       331-1059   56.1   0.8   0.079       331-1061   51.8   0.96   0.095       331-1061   43.4   0.89   0.086       331-1061   50.7   0.93   0.098       331-1062   49.3   1.01   0.102       331-1062   45.5   1   0.118       331-1062   39.7   0.97   0.095       331-1065   45.8   0.78   0.088       331-1065   50.8   0.82   0.076       331-1065   55.8   0.81   0.055       331-1060   47.8   0.85   0.1037       331-1060   51.8   0.81   0.089       331-1064   55.9   0.98   0.064       331-1064   48.9   0.96   0.083       331-1067   52.3   0.82   0.064       331-1067   47.6   0.87   0.063       331-1067   53.2   0.87   0.066       331-1069   49.6   0.89   0.095       331-1069   56.1   0.99   0.1131       331-1072   49.6   0.84   0.054       331-1073   54.4   0.69   0.061       331-1075   51.8   0.91   0.092       331-1075   51   0.88   0.097       331-1075   54.7   0.91   0.085       331-1076   43.4   0.74   0.068       331-1076   53.6   0.76   0.085       331-1077   54.2   0.77   0.038       331-1078   50.7   0.87   0.085       331-1078   51   0.85   0.08       331-1079   55.6   0.98   0.085       331-1079   49.3   0.89   0.1       331-1079   47.6   0.95   0.092       331-1084   51.3   0.91   0.085       331-1084   45.5   0.85   0.074       331-1086   44.1   0.82   0.083       331-1086   48.9   0.87   0.079       331-1087   39.7   0.86   0.079       331-1087   39.3   0.85   0.066       331-1087   54.6   0.84   0.085       331-1090   45   0.95   0.076       331-1093   44.5   0.91   0.085       331-1093   48.5   0.75   0.085       331-1093   45.8   0.81   0.065       331-1095   49.1   0.91   0.068       331-1095   50.8   0.77   0.091       331-1101   47.2   0.93   0.095       331-1101   55.2   0.96   0.082#       331-1101   55.8   0.92   0.076       331-1102   43.5   0.73   0.073       331-1102   47.7   0.82   0.083       331-1103   46.2   0.81   0.085       331-1103   49.6   0.92   0.09       331-1103   50.7   0.95   0.081       331-1104   44.1   0.81   0.066       331-1104   51.5   0.82   0.054       331-1106   52   0.68   0.075       331-1106   50.8   0.79   0.068       331-1112   48.2   0.6   0.077       331-1112   50.8   0.75   0.078       331-1112   49.9   0.76   0.065       331-1114   51.3   0.87   0.102       331-1114   48.1   0.98   0.099       331-1114   50.5   0.99   0.118       331-1118   46.9   0.81   0.098       331-1118   51   0.99   0.078       331-1120   50.9   0.83   0.065       331-1121   48.2   0.54   0.055       331-1122   51.9   0.84   0.062       331-1122   47   0.78   0.077       331-1122   45.9   0.77   0.064       331-1126   52.7   1.03   0.113       331-1126   52.4   0.98   0.099       331-1126   44   0.93   0.098       331-1127   47.2   0.87   0.102       331-1127   50.9   1.01   0.124       331-1127   48.4   1.02   0.075       331-1128   53.2   0.9   0.085       331-1128   46.8   0.85   0.085       331-1128   39.7   0.85   0.082       331-1130   47.8   0.85   0.083       331-1130   48.9   0.92   0.079       331-1130   51.8   0.93   0.103       331-1131   44.1   0.99   0.098       331-1131   55.9   0.96   0.085       331-1133   45.5   0.76   0.078       331-1133   48.9   0.69   0.069       331-1136   51.3   0.64   0.077       331-1136   52.3   0.69   0.082       331-1140   56.1   0.8   0.081       331-1140   54.2   0.78   0.086       331-1149   51   0.91   0.123       331-1149   46.9   0.94   0.122       331-1149   55.2   0.94   0.118       331-1151   45.8   0.77   0.042       331-1151   47.6   0.94   0.106       331-1151   54.4   0.91   0.117       331-1158   48.1   0.75   0.064       331-1158   51   0.7   0.083       331-1158   52   0.77   0.075       331-1162   50.7   0.81   0.078       331-1162   47.2   0.89   0.087       331-1162   52.4   0.94   0.085       331-1163   50.5   0.62   0.05       331-1163   48.3   0.65   0.054       331-1169   44.8   0.71   0.085       331-1169   47.9   0.78   0.091       331-1169   45.9   0.8   0.121       331-1173   49.9   0.96   0.092       331-1173   49.1   0.81   0.075       331-1173   50.8   0.91   0.092       331-1174   46.2   0.85   0.093       331-1174   51.2   0.88   0.124       331-1182   47.6   0.88   0.091       331-1186   45.8   0.91   0.089       331-1186   52.6   0.95   0.084       331-1186   44.9   0.99   0.077       331-1580   53.2   0.67   0.075       331-1580   51.7   0.72   0.081       331-1580   48.1   0.79   0.066       331-1582   46.8   0.86   0.075       331-1582   51.6   1.01   0.068       331-1582   47.3   0.94   0.075       331-1587   52.8   0.85   0.076       331-1587   50.5   0.91   0.075        14-1292.1   34.8   0.77   0.077   Boardman - B        14-1293.2   39.6   0.75   0.095   Clatskanie - C        14-1294.1B   42.3   0.67   0.113        93-9682.2   46.9   0.86   0.11        93-9682.1   42.3   0.79   0.092        93-9683.1   45.9   0.72   0.105        93-9683.2   49   0.73   0.088        93-9684.1B   55.5   0.79   0.098        93-9684.2B   58.3   0.81   0.1        53-2422.2   53.3   0.74   0.101        53-2423.1   51   0.71   0.087        53-2423.2   53.2   0.7   0.12        53-2424.1B   53.2   0.71   0.08        53-2461.1   46.2   0.65   0.18        53-2461.2   46.3   0.66   0.097        53-2462.1   50.6   0.64   0.087        53-2464.1B   56.7   0.68   0.073       10591.1   28   0.6   0.087       10591.2   37.2   0.6   0.146       10593.2B   58.1   0.61   0.103       10594.1B   46.2   0.73   0.123       10601.1   47.5   0.6   0.094       10601.2   50   0.61   0.106       10602.1   49.5   0.66   0.119       10602.2   54.2   0.72   0.111       10603.2B   48.3   0.54   0.057       10604.2B   43.3   0.56   0.099       10611.1   47.9   0.79   0.079       10611.2   47.6   0.79   0.117       10614.1B   47.7   0.79   0.097       10614.2B   50   0.75   0.044       10622.1   49.5   0.79   0.114       10622.2   54.2   0.71   0.097       10624.1B   48.3   0.59   0.068       10624.2B   43.3   0.51   0.092       10653.1   47.9   0.69   0.105       10653.2   47.6   0.66   0.094       10654.1B   47.7   0.74   0.156       10654.2B   34.8   0.74   0.175       10671.1   34.8   0.68   0.098       10671.2   39.6   0.68   0.128       10674.1B   42.3   0.64   0.075       10674.2B   46.9   0.65   0.071       10693.1   42.3   0.67   0.211       10693.1B   45.9   0.69   0.139       10693.2B   47.5   0.68   0.129       10721.2   50   0.63   0.138       10722.1   49.5   0.72   0.147       10722.2   54.2   0.71   0.131       10724.1B   48.3   0.72   0.139       10724.2B   43.3   0.67   0.149       10731.1   47.9   0.66   0.242       10731.2   47.6   0.65   0.241       10732.2   47.7   0.64   0.234       10734.1B   38   0.67   0.201       10734.2B   43.2   0.56   0.111       10751.1   27.2   0.66   0.114       10751.2   50.6   0.74   0.076       10754.1B   50   0.78   0.087       10754.2B   48.7   0.66   0.108       10762.1   50.4   0.55   0.11       10762.2   41   0.63   0.131       10772.2   49.5   0.56   0.103       10781.1   43.1   0.48   0.135       10781.2   50.4   0.52   0.219       10784.1B   47.3   0.72   0.214       10784.2B   36.7   0.6   0.186       10791.1   53   0.69   0.114       10791.2   58.1   0.7   0.123       10794.1B   46.2   0.75   0.107       10794.2B   47.5   0.82   0.114       10841.1   50   0.74   0.093       10841.2   49.5   0.73   0.108       10844.1B   54.2   0.69   0.081       10844.2B   48.3   0.74   0.094       10861.1   43.3   0.7   0.086       10861.2   47.9   0.62   0.113       10864.1B   47.6   0.62   0.114       10864.2B   47.7   0.59   0.132       10872.1   34.8   0.69   0.113       10872.2   39.6   0.71   0.083       10874.1B   42.3   0.73   0.093       10874.2B   46.9   0.72   0.095       10902.1   42.3   0.79   0.089       10902.2   45.9   0.74   0.067       10904.1B   55.5   0.87   0.091       10904.2B   58.3   0.8   0.083       10931.1   53.3   0.62   0.099       10931.2   51   0.58   0.075       10934.1B   53.2   0.67   0.095       10934.2B   53.2   0.63   0.086       10951.1   46.2   0.63   0.093       10951.2   46.3   0.8   0.109       10954.1B   50.6   0.77   0.084       10954.2B   56.7   0.62   0.082       11011.1   28   0.76   0.093       11012.2   37.2   0.73   0.104       11014.2B   58.1   0.74   0.099       11021.1   46.2   0.69   0.109       11021.2   46.2   0.68   0.081       11023.1B   47.5   0.7   0.093       11031.1   50   0.74   0.084       11031.2   49.5   0.73   0.086       11034.1B   54.2   0.74   0.091       11034.2B   48.3   0.85   0.09       11041.1   43.3   0.73   0.113       11041.2   47.9   0.74   0.073       11044.1B   47.6   0.72   0.101       11044.2B   47.7   0.7   0.087       11121.1   38   0.5   0.12       11123.1   43.2   0.62   0.08       11124.2B   27.2   0.38   0.18       11142.1   50.6   0.74   0.097       11142.2   50   0.78   0.087       11144.1B   48.7   0.76   0.073       11144.2B   50.4   0.86   0.087       11181.1   41   0.6   0.146       11182.1   49.5   0.68   0.103       11184.1B   43.1   0.56   0.123       11184.2B   50.4   0.6   0.094       11201.1   50.9   0.65   0.106       11201.2   47.3   0.55   0.119       11211.1   49.3   0.59   0.111       11214.1B   46.1   0.64   0.057       11214.2B   45.4   0.66   0.099       11221.1   44.1   0.63   0.079       11221.2   49.1   0.62   0.117       11223.2B   44   0.59   0.097       11224.2B   51.2   0.57   0.044       11261.2   44.3   0.78   0.114       11262.1   51.3   0.82   0.097       11264.1B   47.3   0.86   0.068       11264.2B   36.7   0.8   0.092       11271.1   46.1   0.69   0.105       11271.2   45.4   0.71   0.094       11274.1B   46.6   0.66   0.156       11274.2B   43.2   0.62   0.175       11282.1   35   0.79   0.098       11282.2   52.4   0.78   0.128       11284.1B   50   0.82   0.075       11284.2B   39   0.87   0.071       11302.1   39.6   0.72   0.211       11302.2   42.3   0.66   0.139       11311.1   46.9   0.71   0.129       11311.2   42.3   0.73   0.138       11312.1   45.9   0.64   0.147       11313.2B   27.2   0.67   0.131       11334.1B   50.6   0.64   0.139       11334.2B   44.3   0.65   0.149       11361.1   45.4   0.6   0.242       11361.2   44.1   0.56   0.241       11362.2   49.1   0.53   0.234       11401.1   44   0.55   0.201       11402.1   51.2   0.61   0.111       11402.2   44.3   0.62   0.114       11404.1B   51.3   0.64   0.076       11404.2B   51.4   0.74   0.087       11491.1   37.1   0.74   0.108       11491.2   49.4   0.79   0.11       11492.1   50.8   0.68   0.131       11494.1B   35.5   0.65   0.103       11494.2B   46.5   0.7   0.135       11511.1   47.2   0.59   0.219       11511.2   46.6   0.71   0.214       11511.22   43.2   0.69   0.186       11514.1B   35   0.8   0.114       11581.1   52.4   0.62   0.123       11581.2   50   0.67   0.107       11583.1B   39   0.61   0.114       11583.2B   51.4   0.77   0.093       11584.2B   37.1   0.59   0.108       11621.2   49.4   0.7   0.081       11622.1   50.8   0.69   0.094       11624.1B   35.5   0.48   0.086       11631.1   46.5   0.61   0.113       11631.2   47.2   0.64   0.114       11634.1B   46.6   0.48   0.132       11634.2B   43.2   0.54   0.113       11653.1   35   0.53   0.083       11691.1   52.4   0.63   0.093       11691.2   49.3   0.55   0.095       11694.1B   58.9   0.66   0.089       11694.2B   52.2   0.69   0.067       11732.1   49.8   0.6   0.091       11732.2   46.5   0.65   0.083       11733.1   46.6   0.56   0.099       11733.2   50.3   0.61   0.075       11734.1B   47.6   0.69   0.095       11734.2B   48.4   0.67   0.086       11741.1   52.7   0.68   0.093       11741.2   48   0.57   0.109       11862.1   50.9   0.74   0.084       11862.2   47.3   0.7   0.082       15803.1   49.3   0.6   0.093       15803.2   46.1   0.53   0.104       15804.1B   45.4   0.62   0.099       15804.2B   44.1   0.65   0.109       15823.1   49.1   0.78   0.081       15823.2   44   0.74   0.093       15823.1B   51.2   0.72   0.084       15823.2B   44.3   0.66   0.086       15871.1   51.3   0.69   0.091       15871.2   47.3   0.65   0.09       15874.1B   36.7   0.49   0.113       15874.2B   53   0.63   0.073                  
 
         [0173]    Previous experiments have shown no difference in the fiber properties analyses of poplar samples between these two instruments [Robertson, G., Olson, J., Allen, P., Chan, B. and Seth, R. “Measurement of fiber length, coarseness and shape with the fiber quality analyzer”. TAPPI J. 82(10), 93-98 (1999)]. The outermost ring (age 7) data are presented in Table I. Microfibril angle data for the outermost ring of each core (i.e. age 7), obtained using the SilvisScan-2 technique, are also presented in Table II. FIG. 1 shows the results of a typical SilviScan-2 analysis of an increment core sample from bark to pith at different levels of scanning resolution.  
                                           TABLE II                           Microfibril angle data for hybrid poplars at age 7.                TREE   MFA           331-   Ring 7 data                            1060   29.22           1063   26.15           1064   30.45           1065   27.13           1067   32.09           1069   29.09           1072   30.06           1073   32.24           1075   33.55           1076   34.60           1078   29.58           1079   31.25           1080   23.40           1082   28.43           1084   28.90           1095   30.58           1101   25.48           1103   28.03           1104   35.26           1114   21.56           1120   25.75           1122   17.76           1126   26.14           1127   33.37           1128   25.15           1130   25.87           1131   25.30           1140   24.98           1149   28.42           1151   28.59           1158   25.92           1169   26.54           1174   25.25           1186   27.01           1580   38.19           1590   20.84           1591   30.02           1592   26.09           1593   26.51                      
 
         [0174]    Significant variability is seen for all three traits—fiber coarseness ranges from 0.042 mg/m to 0.124 mg/m; microfibril angle from 17.8° to 38.2°; maceration yield from 27.2% to 56.1%. Results of the Mapmaker-QTL 1.1 analysis of the data are shown in Table ll. One significant QTL has been found for fiber coarseness, one low significance QTL for microfibril angle and four for macerated pulp yield. The QTL for each fiber property are concident and one of the QTL for maceration yield (P1027_P192/R) is coincident with the low significance QTL detected for Kraft pulp yield (Table VI). These regions may, therefore, represent particularly important areas of the genome for pulp and paper properties.  
                                                                           TABLE III                           Significant QTL detected for each examined property            Trait   Marker/Linkage   LOD Score*   Phen % ‡     Length/cM   Weight   Dom.                    Fiber   I14_09-F15_10/E   3.49   55.9   37.3   72.794   −79.906       Coarseness       Microfibril   I14_09-F15_10/E    2.38*   39.8   37.3   0.9445   4.4460       angle       Maceration   P1258-P75/C   3.50   68.8   3.3   −6.3878   6.4285       yield           I17_04-P1275/J   3.18   75.4   15.4   −5.3740   7.8547           P1218-G02_11/J   4.26   73.4   13.8   −5.7903   7.9257           P1027-P192/R   2.98   50.0   0.0   −2.8721   5.7712                                          
 
         [0175]    Lignin Composition  
         [0176]    Data for the lignin compositional analyses undertaken on the core samples are presented in Table IV.  
                                           TABLE IV                           Lignin contents for the harvested stems                Clone   Lignin (%)                             14-129   24.56            93-968   25.57            53-242   23.31            53-246   24.50           331-1059   24.89           331-1061   25.75           331-1062   24.78           331-1075   24.87           331-1093   25.43           331-1118   23.99           331-1122   24.27           331-1126   23.38           331-1136   24.56           331-1162   22.93           331-1186   24.71                      
 
         [0177]    These phenotypic data were used in a Mapmaker-QTL 1.1 genetic mapping experiment which resulted in the identification of a single, significant QTL for lignin content (shown in Table V). Due to the extensive industrial and academic interest in the genetic control of this particular woody plant trait, many candidate genes for this region—primarily from the lignin biosynthetic pathway—have already been sequenced, a fact which may enable the rapid characterization of this QTL.  
                                             TABLE V                           Significant QTL detected for lignin content            Trait   Marker/Linkage   LOD Score   Phen %   Length/cM   Weight   Dom.               Lignin content   P757-P867/P   3.32   24.7   16.7   0.5463   −0.0099                  
 
         [0178]    Extractives Content—GC/MS Analysis  
                                                                           TABLE VI                           Significant QTL detected for individual extractives peaks            Trait                               Compound   Marker/Linkage   LOD Score   Phen %   Length/cM   Weight   Dom.                    Beta-   P1277-P12612/A   9.84   83.3   14.7   4.7882   −5.8067       sitosterol       (r.t. 25.831)   P856-A18_06/I   7.97   81.3   14.0   4.9972   −5.5280           win8-G04_20/I   10.47   81.3   27.0   5.0064   −5.5178           P1202-P1221/O   5.60   80.7   15.8   −5.3093   −4.9808       Sterol   P1277-P12612/A   5.03   69.4   14.7   −0.9132   −1.1720       (r.t. 25.912)   P1011-C04_04/A   5.70   68.8   23.5   −0.9541   −1.1478           P1322-P1310/A   4.12   67.6   12.2   −1.0231   −0.9421           P1074-G12_15/B   5.76   65.1   19.7   −1.5614   −1.4403           P44-P1054/B   6.04   65.4   4.4   −1.5744   −1.4237           H12_03-P1196/B   3.71   58.8   8.8   −1.2545   −1.0949           win8-G04_20/I   5.16   64.7   27.0   1.5482   −1.4744           G13_17-C10_21/I   5.91   64.4   14.0   1.4861   −1.5144           P65-P1203/J   4.86   64.6   9.1   1.5060   −1.5576           B15_17-P216/X   2.97   31.5   0.4   −0.5213   −0.6455       Sterol   win8-G04_20/I   9.06   72.2   27.0   3.8061   −3.6553       (r.t. 25.917)   G13_17-C10_21/I   9.20   72.0   14.0   3.7236   −3.8242           I17_04-P1275/J   8.86   72.2   15.4   3.8034   −3.6422           P773-P1055/J   7.17   72.2   3.9   3.8033   −3.6495           P65-P1203/J   9.21   72.0   9.1   3.7858   −3.6910           P1218-G02_11/J   9.55   71.9   13.8   3.7620   −3.7391       Sterol   P1277-P12612/A   12.12   90.1   14.7   −0.1879   −0.3996       (r.t. 26.319)   H19_08-E14_15/C   6.53   81.7   19.7   0.3026   −0.2430           P12182-P1049/C   5.17   75.3   19.0   −0.2181   −0.2372           P13292-P1043/M   6.27   79.2   12.0   −0.2791   −0.2991           P46-F15_18/X   8.18   80.3   17.9   −0.2996   −0.2567           E18_05-P12743/X   5.00   80.3   11.5   −0.3007   −0.2567           P1064-B15_17/X   7.97   81.2   26.6   −0.3044   −0.2468       Sterol/triter   P1277-P12612/A   5.30   80.2   14.7   0.0157   −0.1606       pene       (r.t. 26.417)   H19_08-E14_15/C   6.53   80.0   19.7   0.0858   −0.0726           P12182-P1049/C   3.20   77.1   19.0   −0.0730   −0.1091           P1018-P12242/E   4.80   80.2   16.9   −0.0705   −0.0957           P1064-B15_17/X   3.14   80.2   26.6   −0.0782   −0.0829       Sterol   I14_09-F15_10/E   3.35   65.3   37.3   0.1014   −0.0849       (r.t. 27.818)   I17_04-P1275/J   3.46   63.9   15.4   0.0967   −0.0985           P1218-G02_11/J   4.34   63.5   13.8   0.0959   −0.1006           E18_15-C01_16/M   3.15   68.7   22.1   −0.1074   −0.0778       Sterol/triter   P1277-P12612/A   18.15   95.3   14.7   1.6108   −1.6355       pene       (r.t. 28.218)   P1011-C04_04/A   18.99   97.3   23.5   1.5192   −1.7546           P1291-P1267/L   18.13   95.5   12.9   1.5951   −1.6614       Triterpene/   P1145-G08_09/M   3.96   78.4   12.7   −2.6340   −2.3716       ester       (r.t. 37.833)   E18_15-C01_16/M   3.76   77.1   22.1   2.5955   −3.5004           P1064-B15_17/X   4.72   81.1   26.6   −2.6098   −3.6878       Triglyceride   P11642-P1145/M   3.13   56.3   4.5   −1.3120   −2.0510       (r.t. 40.084)                  
 
         [0179]    The GCMS method used for compound analysis was that developed and optimized by Fernandez et al. for the analysis of aspen ( P. tremuloides ) extractives. Peaks were identified via retention time and ion masses. The area of particular interest in the spectrum—containing the sterols and assorted waxes, compounds which are implicated in pitch formation propensity—was delineated as shown in FIG. 2A, at retention times greater than 25 min. The similarity between this aspen spectrum and those obtained from the hybrid poplar clones—a typical spectrum is shown in FIG. 2B—allowed the extrapolation of peak identification table data to the mapping population clones. Identified compounds were quantified, ratio numbers were obtained relative to the internal standard and were then used for QTL experiments. Significant QTL for extractives peaks are presented in Table V.  
         [0180]    To date, this application has successfully identified a number of QTL that contain genes involved in the control of sterol and steryl ester content/synthesis in this family of hybrid poplars. The fact that several QTL have been independently detected for a number of related compounds provides strong evidence that the synthesis of a suite of related compounds is controlled by the same discrete genetic regions (implying the existence of a biosynthetic pathway) and that these QTL in particular may be regarded as non-spurious detections. These results both confirm and extend the conclusions of previous research describing clonal-based variation of extractives content in a natural population of aspen ( P. tremuloides ).  
         [0181]    Chipping and Chip Quality of Hybrid Poplar Stems  
         [0182]    Whole logs of selected hybrid poplar clones were debarked and chipped as described in the experimental section. The wood density and chip quality of selected clones are presented in Table VII. Attempted correlations between the accept chip fraction and the wood density were unsuccessful (FIG. 3).  
                                                                                                   TABLE VII                           Wood density and Chip Quality of Selected Clones                93-   53-   53-   331-   331-   331-   331-   331-   331-           968   242   246   1059   1061   1062   1075   1122   1186                    Wood Density (kg/m 3 )   309   316   318   303   337   285   300   283   292       45 mm round (%)   0.9   4.3   4.5   2.9   1.4   1.4   2.9   0.2   1.8        8 mm slot (%)   15.2   15.1   18.4   21.8   9.8   16.5   20.0   14.2   17.1        7 mm round (%)   81.5   79.4   76.0   74.0   83.1   80.5   75.8   82.7   78.7        3 mm round (%)   2.0   1.0   0.8   1.0   2.5   1.2   0.8   2.2   1.8       Fines (%)   0.6   0.4   0.4   0.4   0.5   0.5   0.5   0.7   0.6                  
 
         [0183]    [0183]FIG. 4 shows a plot of chip density against bulk density (Table VIII) for the sampled stems.  
                                                   TABLE VIII                           Hybrid Poplar Chip Density And Chip Packing Density       (Bulk Density) Puyallup, Washington Site                    Chip Density   Bulk Density           Sample Air Dried Chips   Kg/m 3      Kg/m 3                               14-129 (1)   0.285   130.7            14-129 (2)   0.304   145.1            53-242 (1)   0.329   167.5            53-242 (2)   0.302   143.9            53-246 (1)   0.311   151.0            53-246 (2)   0.325   162.6            93-968 (1)   0.303   153.3            93-968 (2)   0.314   146.5           331-1059 (2)   0.303   137.5           331-1059 (3)   0.302   142.3           331-1061 (1)   0.338   176.1           331-1061 (2)   0.328   161.4           331-1061 (3)   0.345   174.3           331-1062 (1)   0.280   133.8           331-1062 (2)   0.290   136.2           331-1075 (2)   0.300   140.8           331-1093 (1)   0.279   132.1           331-1093 (2)   0.288   134.8           331-1118 (1)   0.346   165.7           331-1118 (2)   0.373   173.3           331-1122 (1)   0.283   133.5           331-1126 (1)   0.386   188.0           331-1136 (1)   0.288   146.5           331-1162 (3)   0.336   155.4           331-1186 (3)   0.292   144.7                                                          
 
         [0184]    The two parameters are related by a Pearson correlation coefficient of 0.86 (p=0.000). Higher density chips, such as those obtained from clone 331-1061, are more desirable as they pack better into kraft pulp digesters and mechanical pulp mill plug screw feeders thus ensuring maximum mill production rates. If these clones were to be ranked on the basis of chip value and quality (i.e. low oversized, pins and fines fractions), clones 331-1061, 331-1122, parent 93-968 and triploid 331-1062 would be considered superior material.  
         [0185]    Kraft Pulping and Testing  
         [0186]    1. Pulping Data  
         [0187]    The 25 hybrid poplar trees (comprising 15 distinct genotypes) were chemically pulped according to the conditions outlined above and handsheets were prepared from the corresponding pulps. Calculated data for pulping to Kappa 17, derived from Table IX, are presented in Table X.  
                                                                           TABLE IX                           Hybrid Poplar Exploratory Kraft Pulping Data (whole log chip samples)            Sample   Kappa   % Unsc&#39;d Yield   H Factor   % Res. EA   % EA Consumed   % Rejects                     14-   27.1   55.9   800   3.0   10.0   0.7        129(1)           17.9   54.9   1100   2.8   10.2   trace           15.6   53.8   1400   2.5   10.5   0.1        14-   32.2   57.6   700   3.1   9.9   4.7        129(2)           23.1   55.1   1000   2.6   10.4   1.1           17.5   53.6   1400   2.2   10.8   0.1       331-   30.0   56.5   700   2.7   10.3   3.2       1059(2)           19.6   54.8   1000   2.3   10.7   0.3           15.2   54.1   1400   2.1   10.9   0.2       331-   24.6   55.4   800   2.5   10.5   0.4       1059(3)           17.8   54.1   1100   2.2   10.8   0.2           14.9   53.6   1400   2.0   11.0   0.4       331-   28.8   54.9   800   2.4   10.6   1.0       1061(1)           20.9   53.9   1100   2.2   10.8   0.1           17.9   52.8   1400   2.0   11.0   trace       331-   27.9   55.5   800   2.5   10.5   1.5       1061(2)           17.5   54.2   1100   2.3   10.7   trace           15.0   53.4   1400   2.1   10.9   trace       331-   25.3   55.2   800   2.5   10.5   0.5       1061(3)           18.3   54.6   1100   2.3   10.7   0.2           15.3   53.5   1400   2.0   11.0   0.3       331-   25.7   55.5   800   2.7   10.3   2.4       1062(1)           18.9   53.7   1100   2.3   10.7   0.5           14.8   53.2   1400   2.1   10.9   trace       331-   25.2   54.6   800   2.5   10.5   0.9       1062(2)           18.0   53.0   1100   2.2   10.8   0.4           15.1   52.6   1400   2.1   10.9   trace       331-   33.3   56.0   700   2.7   10.3   5.4       1075(2)           23.6   53.9   1000   2.4   10.6   0.7           17.0   53.2   1400   2.1   10.9   0.5       331-   27.7   54.8   800   2.6   10.4   1.7       1093(1)           20.7   53.3   1100   2.3   10.7   0.4           17.7   53.1   1400   2.2   10.8   0.5       331-   25.7   54.7   800   2.6   10.4   1.0       1093(2)           17.9   53.6   1100   2.3   10.7   0.4           15.8   52.3   1400   2.0   11.0   trace       331-   25.8   56.2   705   2.8   10.2   1.3       1118(1)           18.7   56.0   1000   2.6   10.4   0.4           14.3   54.7   1400   2.2   10.8   0.1       331-   25.1   56.0   800   2.8   10.2   1.3       1118(2)           20.7   55.0   1000   2.5   10.5   0.4           15.4   54.3   1400   2.3   10.7   0.1       331-   25.8   55.3   800   2.5   10.5   1.6       1122(1)           18.7   53.7   1100   2.2   10.8   0.1           14.6   53.3   1400   2.1   10.9   0.1       331-   23.2   55.8   800   2.8   10.2   1.1       1126(1)           18.1   54.4   1100   2.5   10.5   0.1           14.7   54.1   1400   2.3   10.7   trace       331-   38.6   54.7   800   2.1   10.9   5.4       1136(1)           25.7   52.6   1100   1.9   12.1   1.7           20.7   51.6   1400   1.8   12.2   1.1           18.0   51.4   1634   1.7   11.3   na       331-   24.1   54.9   800   2.9   10.1   0.5       1162(3)           17.1   53.4   1100   2.6   10.4   trace           14.0   52.8   1400   2.4   10.6   trace       331-   24.3   56.1   800   2.7   10.3   0.6       1186(3)           17.3   54.4   1100   2.4   10.6   trace           14.2   54.4   1400   2.2   10.8   0.1        53-   21.5   56.0   800   2.6   10.4   0.8        242(1)           16.9   54.5   1100   2.3   10.7   0.2           14.1   54.0   1400   2.1   10.9   trace        53-   23.0   56.5   800   2.7   10.3   2.7        242(2)           16.9   55.5   1100   2.5   10.5   1.0           16.4   55.1   1400   2.3   10.7   2.4        53-   23.3   55.9   800   2.7   10.3   1.4        246(1)           16.4   54.8   1100   2.4   10.6   0.2           14.2   54.0   1400   2.2   10.8   trace        53-   23.1   56.6   800   2.7   10.3   1.0        246(2)           17.4   56.1   1100   2.5   10.5   0.9           12.8   55.2   1400   2.4   10.6   trace        93-   22.6   58.0   800   2.8   10.2   2.4        968(1)           16.7   56.6   1100   2.6   10.4   0.2           14.2   55.5   1400   2.2   10.8   trace        93-   18.8   58.5   800   3.1   9.9   0.9        968(2)           13.2   57.4   1100   2.8   10.2   0.1           11.9   56.1   1400   2.5   10.5   trace                  
 
         [0188]    [0188]                                                   TABLE X                           Kraft pulping data for harvested stems (Kappa 17)                H-Factor   Unscreened Yield (%)   % EA Consumed                     14-129   1230   54.4   10.3           1436   53.5   10.9       ? 93-968   1110   56.5   10.5           883   58.0   10.0       ? 53-242   1092   54.7   10.7           1211   55.4   10.6       ? 53-246   1112   54.7   10.6           1088   55.9   10.5       331-1059   1213   54.4   10.8           1190   54.0   10.9       331-1061   1448   52.9   11.0           1200   53.9   10.8           1225   54.0   10.8       331-1062   1219   53.3   10.8           1207   52.9   10.8       331-1075   1401   53.0   10.9       331-1093   1443   52.8   10.9           1236   52.9   10.8       ?331-1118   1135   55.3   10.6           1251   54.5   10.6       331-1122   1206   53.6   10.8       331-1126   1177   54.4   10.5       331-1136   1684   51.1   11.3       331-1162   1132   53.4   10.4       ?331-1186   1146   54.7   10.6                            
         [0189]    [0189]FIG. 5 shows the relationship between H-factor and Kappa number for the pulped stems. In FIG. 4, population parents 93-968 and 14-129 form the boundaries of the variability seen in kappa number at each H-factor value. It is clear that, as was the case for aspen, the variation in H-factor required to achieve a given Kappa number is substantial. For example, to achieve Kappa 17, clone 331-1136 requires approximately 1650H-factor whereas clone 93-968 requires only 1000H-factor (a 40% reduction).  
         [0190]    The particular difficulty in pulping clone 331-1136 indicated here may be a function of this clone&#39;s high level of calcium accumulation (see below), particularly as this clone&#39;s lignin content is not unusually high (24.56% in a population range of 22.93-25.75%, see Table IV. Also like aspen, the swings in yield at a given unbleached kappa number are substantial. All the exploratory kraft pulping data are presented in Table X herewith. At kappa 17 the yield from clone 331-1136 was approximately 51%. This may be an outlier point (excess compression wood due to plantation location, etc.). The lower limit of pulp yield is probably better represented by clones 331-1093 and 331-1062 whereas clone 93-968 exhibits a 57% pulp yield (FIG. 6). In FIG. 6, parent 93-968 (pure  P. trichocarpa ) forms a distinct envelope whereas the remainder of the clones examined resemble parent 14-129 ( P. deltoides ). Superior clones are highlighted in Table X. The relationship between ease of pulping and pulp yield is evident (Pearson correlation of −0.828, p=0.000).  
         [0191]    However it should be noted that the variability in yield at a given H-factor is high as evidenced by the relatively poor R 2  of 0.69, shown in FIG. 7. In FIG. 7, it can be seen that the Parental clones represent the extremes, (clonal lignin content 25.75-22.93%) 331-1162 has the lowest lignin content but gives low pulp yield and average pulping rate, therefore lignin content is not a reliable indicator of pulpability. These results confirm the necessity to pilot pulp clones for proper evaluation of properties. Further, the H-factor required to achieve kappa 17 has been evaluated against the chip density in FIG. 8. It is clear that in addition to lignin content wood density cannot be used to predict ease of kraft pulping (Pearson coefficient −0.194, p=1.000).  
         [0192]    Table XI presents the fiber properties data obtained for the pulped clones at Kappa 17. The top three ranked clones in terms of high length and low coarseness are indicated in bold.  
                                                   TABLE XI                           Whole stem pulp fibre properties data                    LW Fiber Length   Coarseness               (mm)   (mg/m)                             14-129   0.65   0.103               0.69   0.115            93-968   0.66   0.097               0.76   0.113              53-242       0.69       0.099                 0.76   0.109            53-246   0.73   0.105               0.74   0.103             331-1059       0.67       0.087                 0.65   0.092             331-1061       0.68       0.097                 0.64   0.094               0.71   0.101           ?331-1062   ?0.80   ?0.121               0.82   0.121             331-1075       0.69       0.097               331-1093       0.53       0.083                 0.57   0.083           331-1118   0.78   0.105               0.61   0.101           ?331-1122   ?0.79   ?0.122           331-1126   0.79   0.102           331-1136   0.46   0.117           ?331-1162   ?0.80   ?0.121           331-1186   0.68   0.099                                              
 
         [0193]    A positive correlation (Pearson coefficient 0.543, p=0.105) can be seen between the fiber length and coarseness data which mirrors that seen for the 7 th  year ring data and the situation seen in aspen populations (FIG. 9). In FIG. 9, the positive correlation seen here is in contrast to that seen for aspen clones but supports the data obtained for the 7 th  year growth ring from each hybrid poplar in the previous study. If the outlier point for clone 331-1136 is omitted from the analysis, the correlation becomes much more significant (Pearson coefficient 0.834, p=0.000).  
         [0194]    The length-weighted fiber length data were also correlated to chip density values, as shown in FIG. 10. Not unexpectedly, and bearing in mind the fiber length: coarseness relationship, the relationship is poor (Pearson coefficient 0.228, p=1.000) even if outlier points are excluded.  
         [0195]    Pulp yield data at kappa 17, were used in a Mapmaker-QTL 1.1 analysis which revealed the presence of a single, low significance QTL for this property—Table XII. The pilot-scale pulping of further clones will likely enhance the statistical significance of the detection of this QTL. Significantly, the QTL kraft pulp yield (the most important trait from an industrial production point of view) correlate with a higher significance QTL for maceration yield but does not coincide with the lignin QTL (Table V).  
                                             TABLE XII                           Low significance QTL detected for Kraft pulp yield            Trait   Marker/Linkage   LOD Score   Phen %   Length/cM   Weight   Dom.               Kraft pulp yield   P1027-P192/R   2.52*   72.7   0.0   −1.8932   0.7270                  
 
         [0196]    H-factor to kappa 17 data from Table IX were also used in a Mapmaker QTL1.1 analysis. However, no significant QTLs were observed which confirms that, not surprisingly, lignin content is not the single controlling factor in kraft pulping of hybrid poplar. There may be concern that this observation does not seem to relate to measurable physical properties. However, issues such as pulping liquor diffusion are also known to be a major contributor to ease of kraft pulping.  
         [0197]    2. Kraft Pulp Properties  
         [0198]    Kraft Pulp Strengths  
         [0199]    The strength of hardwood pulps is becoming an increasingly important parameter given the economic impetus for lighter weight products which retain strength and optical properties and to reduce the amount of expensive softwood Kraft pulp required for many paper grades. Four point PFI mill beater curves were developed for each of the clonal pulps and the results of all tests are presented in Table XIII.  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   TABLE XIII                       Hybrid Poplar Kraft Pulp and Optical Property data                                    14-129 (1)   14-129 (2)   331-1059 (2)            PFI Revolutions   0   1000   3000   6000   0   1000   3000   6000   0   1000   3000   6000               Screened Csf (mL)   499   480   414   361   533   479   423   353   453   435   362   322       Apparent Density (kg/m 3 )   636   703   739   754   618   705   740   767   666   775   784   784       Burst Index (kPa · m 2 /g)   4.7   6.2   7.0   7.6   4.2   5.8   6.6   7.1   6.1   7.9   8.8   9.5       Breaking length (km)   8.7   9.3   10.6   10.5   8.2   9.1   9.7   10.1   9.3   10.6   11.3   11.6       Tensile Index (N · m/g)   85.1   90.9   104.1   103.4   79.9   89.2   95.1   99.2   90.9   104.0   111.1   113.9       Stretch (%)   1.58   2.58   3.44   3.68   1.60   2.71   2.97   3.55   3.11   4.46   5.01   5.26       Tear Index (mN · m 2 /g) (1   6.0   7.2   7.5   7.9   5.6   6.6   7.1   6.7   8.3   9.4   9.0   9.0       Ply)       Tear Index (mN · m 2 /g) (4   7.2   7.6   7.6   7.5   7.7   7.4   7.6   7.4   8.7   9.1   9.0   8.6       Ply)       Zero Span Breaking Length   15.9   15.1   15.8   15.5   15.3   15.6   16.3   16.0   14.0   13.4   13.4   12.8       (km)       Air Resistance (Gurley)   65.0   121.5   206.8   372.4   42.0   85.4   133.4   292.8   130.6   249.6   476.2   862.1       (sec/100 mL)       Sheffield Roughness   89   52   40   27   107   68   52   33   61   31   22   17       (mL/min)       Brightness   37               37               38       Opacity (%)   96.0   95.9   94.4   93.0   97.3   96.1   93.9   92.3   96.8   95.2   94.0   92.1       Scattering Coefficient   311   289   258   229   338   286   242   211   327   266   221   197       (cm 2 /g)                        331-1059 (3)   331-1061 (1)   331-1061 (2)            PFI Revolutions   0   1000   3000   6000   0   1000   3000   6000   0   1000   3000   6000               Screened Csf (mL)   486   454   372   339   524   478   395   346   524   478   395   346       Apparent Density (kg/m 3 )   663   717   757   765   648   721   755   786   682   734   793   807       Burst Index (kPa · m 2 /g)   6.1   7.5   8.2   8.7   4.9   6.1   6.9   7.3   4.9   6.5   7.6   8.1       Breaking length (km)   9.1   9.6   9.9   10.7   8.2   9.2   9.9   10.8   8.3   9.2   10.1   10.8       Tensile Index (N · m/g)   88.8   93.7   97.3   105.0   80.7   90.3   97.4   106.1   81.2   90.3   99.0   105.8       Stretch (%)   2.78   3.91   4.77   7.95   1.96   2.90   3.45   4.25   1.99   3.35   3.73   4.45       Tear Index (mN · m 2 /g) (1   7.5   8.9   8.9   9.0   7.9   8.8   8.4   8.7   6.2   8.0   7.8   8.0       Ply)       Tear Index (mN · m 2 /g) (4   8.2   8.3   8.4   8.4   8.2   8.2   8.5   8.5   7.9   8.3   8.6   8.1       Ply)       Zero Span Breaking Length   14.7   13.9   14.0   13.7   16.3   15.2   15.0   13.7   15.8   16.1   16.2   16.0       (km)       Air Resistance (Gurley)   119.8   177.4   325.0   537.0   75.8   147.3   219.6   449.7   55.1   101.1   201.0   359.9       (sec/100 mL)       Sheffield Roughness   62   40   30   23   79   53   41   27   87   59   37   26       (mL/min)       Brightness   37               35               38       Opacity (%)   96.5   95.0   93.0   91.5   96.4   93.9   93.0   91.9   95.4   94.5   93.1   91.4       Scattering Coefficient   323   253   214   193   298   243   222   200   305   269   232   212       (cm 2 /g)                        331-1061 (3)   331-1062 (1)   331-1062 (2)            PFI Revolutions   0   1000   3000   6000   0   1000   3000   6000   0   1000   3000   6000               Screened Csf (mL)   552   492   420   353   554   536   469   412   561   527   466   397       Apparent Density (kg/m 3 )   625   705   736   748   642   716   745   775   619   702   735   757       Burst Index (kPa · m 2 /g)   4.3   6.1   7.1   7.4   4.9   6.1   7.1   7.6   4.9   6.2   6.7   7.6       Breaking length (km)   7.7   8.8   9.0   10.5   9.2   9.2   10.1   10.8   8.5   9.3   10.1   10.4       Tensile Index (N · m/g)   75.9   86.0   88.7   102.6   89.8   90.6   98.9   106.0   83.3   90.9   98.9   101.7       Stretch (%)   1.69   2.91   3.10   4.13   1.98   2.69   3.44   3.88   1.66   2.83   3.39   3.45       Tear Index (mN · m 2 /g) (1   6.2   9.0   8.6   9.2   8.6   8.7   8.6   8.5   7.2   7.2   7.8   8.4       Ply)       Tear Index (mN · m 2 /g) (4   8.2   9.3   9.0   9.0   8.9   8.7   8.5   8.2   8.7   8.9   8.5   8.2       Ply)       Zero Span Breaking Length   15.9   16.3   15.2   14.2   17.6   17.0   15.7   15.8   15.2   15.0   15.0   15.3       (km)       Air Resistance (Gurley)   28.4   74.8   140.6   234.1   72.5   148.7   279.1   562.1   51.7   115.6   210.5   412.4       (sec/100 mL)       Sheffield Roughness   115   76   55   39   87   55   38   27   109   68   43   28       (mL/min)       Brightness   37               36               37       Opacity (%)   95.2   93.4   92.2   90.9   94.9   93.0   91.6   89.3   95.2   92.5   90.8   89.2       Scattering Coefficient   304   254   229   204   268   221   193   167   286   233   201   179       (cm 2 /g)                        331-1075 (2)   331-1093 (1)   331-1093 (2)            PFI Revolutions   0   1000   3000   6000   0   1000   3000   6000   0   1000   3000   6000               Screened Csf (mL)   483   451   375   328   405   393   336   298   425   403   354   294       Apparent Density (kg/m 3 )   701   781   813   816   734   807   789   861   679   696   742   749       Burst Index (kPa · m 2 /g)   6.2   7.5   8.0   8.5   7.0   8.0   8.7   9.4   6.3   7.7   8.1   8.8       Breaking length (km)   9.8   10.3   10.9   11.5   11.3   11.6   12.2   12.1   10.5   10.2   10.7   11.5       Tensile Index (N · m/g)   96.2   101.3   106.5   113.1   111.2   113.5   119.2   119.0   102.6   99.8   104.8   113.2       Stretch (%)   2.58   3.41   3.97   4.73   2.53   3.77   4.35   4.61   2.71   3.42   3.89   4.80       Tear Index (mN · m 2 /g) (1   8.1   7.9   8.1   7.8   6.7   7.5   7.7   7.8   8.6   7.8   8.4   8.4       Ply)       Tear Index (mN · m 2 /g) (4   9.0   9.1   8.5   8.3   8.3   7.9   8.0   7.4   8.2   8.0   8.1   8.0       Ply)       Zero Span Breaking Length   16.3   14.7   14.3   13.2   15.0   14.7   14.3   13.8   15.7   15.1   14.5   14.1       (km)       Air Resistance (Gurley)   105.9   281.4   510.0   1152.7   274.7   409.6   719.4   1351.2   202.8   527.0   802.0   1378.1       (sec/100 mL)       Sheffield Roughness   61   34   22   15   37   25   17   13   46   25   16   10       (mL /min)       Brightness   35               38               38       Opacity (%)   95.3   93.0   91.8   89.0   96.1   94.2   92.4   91.0   96.1   94.0   92.8   90.3       Scattering Coefficient   287   224   201   169   318   260   230   204   323   260   233   203       (cm 2 /g)                        331-1118 (1)   331-1118 (2)   331-1122 (1)            PFI Revolutions   0   1000   3000   6000   0   1000   3000   6000   0   1000   3000   6000               Screened Csf (mL)   532   487   401   344   573   538   499   443   553   493   453   406       Apparent Density (kg/m 3 )   585   628   692   708   613   701   734   722   660   734   737   780       Burst Index (kPa · m 2 /g)   4.3   5.8   6.8   7.5   4.0   6.1   6.8   7.9   4.6   6.1   6.9   7.4       Breaking length (km)   6.9   8.4   9.5   9.5   7.0   8.4   9.1   10.8   7.8   9.5   9.8   10.2       Tensile Index (N · m/g)   67.2   82.1   92.8   93.5   68.4   82.5   89.6   106.1   76.7   92.8   95.7   99.6       Stretch (%)   2.42   3.86   4.67   4.74   2.01   3.22   4.24   4.80   1.68   3.07   3.52   3.82       Tear Index (mN · m 2 /g) (1   7.1   8.6   8.6   9.1   6.6   8.6   9.5   10.5   7.3   8.8   8.7   8.4       Ply)       Tear Index (mN · m 2 /g) (4   8.6   8.4   8.7   8.8   8.6   9.4   9.5   10.1   8.6   9.0   8.4   8.3       Ply)       Zero Span Breaking Length   13.1   12.7   13.3   13.4   14.1   14.2   14.6   15.2   14.4   14.3   14.0   14.0       (km)       Air Resistance (Gurley)   26.3   65.7   112.5   209.0   13.3   28.8   50.1   101.7   57.4   104.0   244.3   312.5       (sec/100 mL)       Sheffield Roughness   137   88   70   50   142   103   99   65   98   73   50   40       (mL/min)       Brightness   39               38               36       Opacity (%)   97.7   96.0   95.0   93.6   96.7   94.2   92.0   91.1   94.9   92.3   89.8   89.2       Scattering Coefficient   363   290   252   221   345   264   225   197   268   216   185   169       (cm 2 /g)                        331-1126 (1)   331-1136 (1)   331-1162 (3)            PFI Revolutions   0   1000   3000   6000   0   1000   3000   6000   0   1000   3000   6000               Screened Csf (mL)   577   530   476   422   415   409   373   365   497   457   400   346       Apparent Density (kg/m 3 )   609   695   723   742   620   652   690   678   648   707   751   760       Burst Index (kPa · m 2 /g)   3.4   5.4   6.5   7.2   5.9   6.9   7.4   7.6   5.2   6.8   8.1   8.5       Breaking length (km)   6.7   8.0   8.9   10.1   8.8   9.3   10.0   10.6   9.5   10.3   11.2   11.5       Tensile Index (N · m/g)   65.6   78.5   86.9   99.0   86.2   91.2   97.6   104.0   93.4   101.3   109.9   112.3       Stretch (%)   1.47   2.58   3.12   3.83   3.32   3.75   4.51   5.40   2.24   3.25   3.90   4.38       Tear Index (mN · m 2 /g) (1   6.0   8.5   8.2   8.5   7.8   8.5   8.3   8.3   8.5   7.8   8.3   8.3       Ply)       Tear Index (mN · m 2 /g) (4   8.3   9.2   9.1   8.7   8.1   8.0   7.5   7.7   9.8   9.7   9.7   9.7       Ply)       Zero Span Breaking Length   14.9   14.8   14.7   14.7   14.2   14.7   12.9   12.4   16.8   15.5   16.4   16.7       (km)       Air Resistance (Gurley)   10.6   21.3   41.7   65.0   563.9   1128.1   &gt;30   &gt;30   39.0   79.3   152.3   223.8       (sec/100 mL)                           min   min       Sheffield Roughness   161   111   92   76   65   32   20   17   100   68   50   41       (mL/min)       Brightness   38               33               39       Opacity (%)   96.0   94.6   92.8   92.0   95.8   95.0   93.2   91.2   96.7   95.5   94.2   93.6       Scattering Coefficient   323   273   238   219   269   233   195   165   344   292   251   234       (cm 2 /g)                        331-1186 (3)   53-242 (1)   53-242 (2)            PFI Revolutions   0   1000   3000   6000   0   1000   3000   6000   0   1000   3000   6000               Screened Csf (mL)   489   481   418   357   569   510   440   389   513   472   405   350       Apparent Density (kg/m 3 )   673   716   759   770   631   691   723   741   640   722   779   785       Burst Index (kPa · m 2 /g)   6.0   7.3   8.5   8.9   4.6   6.5   7.2   7.7   5.6   7.0   8.0   8.5       Breaking length (km)   9.3   10.2   11.4   11.3   7.8   9.3   9.6   10.4   9.0   10.1   10.4   11.4       Tensile Index (N · m/g)   91.2   100.2   112.0   110.6   76.2   91.5   94.4   102.3   88.5   98.8   102.0   111.6       Stretch (%)   2.25   3.55   4.65   4.59   1.76   3.39   3.68   4.15   2.21   3.18   3.65   4.49       Tear Index (mN · m 2 /g) (1   7.5   8.6   8.7   8.4   7.5   8.3   8.7   8.5   7.7   8.7   8.8   8.4       Ply)       Tear Index (mN · m 2 /g) (4   8.5   8.7   8.2   8.5   8.4   8.6   8.6   8.7   7.8   7.7   7.5   7.6       Ply)       Zero Span Breaking Length   15.4   15.2   15.6   15.2   16.1   16.0   16.5   15.0   14.3   13.4   15.6   14.3       (km)       Air Resistance (Gurley)   79.9   166.7   294.7   538.4   32.1   80.8   148.0   271.4   72.7   136.8   243.2   402.1       (sec/100 mL)       Sheffield Roughness   74   45   36   26   106   71   54   35   81   55   35   28       (mL/min)       Brightness   38               40               39       Opacity (%)   95.7   93.9   92.4   91.3   95.1   92.2   91.0   89.8   95.5   93.6   91.8   90.0       Scattering Coefficient   302   247   222   194   325   250   224   202   301   249   219   193       (cm 2 /g)                        53-246 (1)   53-246 (2)   93-968 (1)            PFI Revolutions   0   1000   3000   6000   0   1000   3000   6000   0   1000   3000   6000               Screened Csf (mL)   549   491   436   385   550   531   468   389   550   508   429   368       Apparent Density (kg/m 3 )   651   710   746   765   615   707   737   775   617   657   720   737       Burst Index (kPa · m 2 /g)   4.3   6.5   7.3   7.7   4.3   6.1   7.2   7.3   5.0   6.4   7.3   7.6       Breaking length (km)   8.1   9.1   10.0   10.0   7.4   8.9   9.1   10.0   9.0   8.9   10.3   10.5       Tensile Index (N · m/g)   79.7   89.2   98.3   98.5   72.6   87.3   89.0   98.5   87.8   87.6   100.9   102.6       Stretch (%)   2.08   3.54   4.15   4.28   2.00   3.59   3.78   4.76   2.11   2.97   3.80   4.11       Tear Index (mN · m 2 /g) (1   7.0   8.2   8.0   8.6   7.1   7.8   8.5   8.1   8.2   8.5   8.7   8.0       Ply)       Tear Index (mN · m 2 /g) (4   7.7   8.3   8.4   8.1   8.2   8.5   8.4   8.2   8.5   8.2   8.0   8.1       Ply)       Zero Span Breaking Length   15.5   14.5   14.7   15.4   14.9   14.6   14.0   15.3   16.2   15.0   15.6   14.9       (km)       Air Resistance (Gurley)   48.2   114.9   195.2   306.4   32.8   77.0   146.0   207.4   39.0   82.2   146.1   261.2       (sec/100 mL)       Sheffield Roughness   92   59   40   30   119   75   54   38   113   76   54   43       (mL/min)       Brightness   40               40               41       Opacity (%)   95.8   93.9   92.5   90.3   96.0   94.8   91.9   91.3   95.4   93.6   92.0   91.0       Scattering Coefficient   341   272   235   211   347   287   240   226   333   282   248   228       (cm 2 /g)                        93-968 (2)                PFI Revolutions   0   1000   3000   6000                       Screened Csf (mL)   468   455   409   340           Apparent Density (kg/m 3 )   555   642   679   690           Burst Index (kPa · m 2 /g)   4.5   6.0   6.9   7.5           Breaking length (km)   8.0   9.2   10.0   10.4           Tensile Index (N · m/g)   78.7   89.9   98.0   101.9           Stretch (%)   1.90   2.95   3.62   3.80           Tear Index (mN · m 2 /g) (1   6.1   7.2   7.6   7.6           Ply)           Tear Index (mN · m 2 /g) (4   6.9   7.2   7.1   7.1           Ply)           Zero Span Breaking Length   14.2   14.7   14.6   14.4           (km)           Air Resistance (Gurley)   51.3   81.1   117.7   190.4           (sec/100 mL)           Sheffield Roughness   131   91   63   50           (mL/min)           Brightness   39           Opacity (%)   95.3   94.2   93.4   92.7           Scattering Coefficient   319   288   263   244           (cm 2 /g)                      
 
         [0200]    In a plot of tensile index vs. bulk, presented in FIG. 11, it can be seen that there is a strong negative correlation between the properties (Pearson coefficient −0.74, p=0.001). In FIG. 11, negative relationship confirms previous aspen data. Most clones show superior strength properties when compared to average values for Eucalyptus species (tensile index 70 N·m/g). More importantly, some clonal pulps (e.g. 331-1122, 1.26 cm 3 /g @ 100 N·m/g) are less bulky at given tensile strengths than are others [e.g. 331-1136, 1.45 cm 3 /g @ 100 N·m/g. (FIG. 12)] This was not predicted from the coarseness data in Table XI (331-1122, 0.122 mg/m vs 331-1136, 0.117 mg/m) and highlights the importance of carrying out pilot scale pulping trials. A coarseness cutoff of &lt;0.1 mg/m is adequate for predicting low bulk/high tensile/fine fibers. It is worth nothing that for pulps prepared from eucalyptus species (the major competitor envisaged for Northern Populus plantation resources)—a tensile index value of 70 N·m/g is considered “standard”. Most of the hybrid poplar pulps examined in this study exceed that strength value even in an unbeaten state (FIG. 13). Additionally, the wide range of tensile indices suggest that there is wide variation in cell wall properties amongst the clones, a possibility which opens up potential multiple end-use applications for the pulps.  
         [0201]    The wide range of cell sizes is further confirmed by the range of tensile indices observed at a given freeness, (a strongly negative relationship between tensile index and freeness properties exists Pearson coefficient −0.74, p=0.001; FIG. 14). Similarly the relationship of air resistance (Gurley) to sheet density, presented in FIG. 15, shows the wide ranging results consequent from cell wall property differences. For example, at beating levels of 6000 PFI revolutions, clones 331-1093 and 331-1075 exhibit the high tensile indices (116.1 and 113.1 N·m/g respectively) coupled with high air resistances (1364.7 and 1152.7 sec/100 mL respectively) which indicate that they possess thinner cell walls than do the other clonal pulps. By contrast, the pulp from clone 53-246 possesses the low tensile index and low air resistance values typical of a thicker cell-walled fiber (98.5 N·m/g, 256.9 sec/100 mL). Interestingly, the high calcium-containing pulp obtained from clone 331-1136 forms an outlier point for this analysis, exhibiting a combination of lower tensile strength (104.0 N·m/g) and very high air resistance (&gt;30 min/100 mL). These variations mirror that seen in a separate study on a population of natural aspen clones. Again the potential for producing pulps for different end-use applications is clear and should be emphasized.  
         [0202]    A number of the kraft pulping properties described here were used in a QTL mapping experiment to attempt to determine the chromosomal locations of any genes involved in the control of these important properties. The outcomes of this analysis are presented in the QTL mapping results section. In terms of sheet formation properties, smoothness shows significant relationships with freeness (Pearson coefficient 0.76, p=0.000) tensile strength (Pearson coefficient −0.87, p=0.000), and sheet density (Pearson coefficient −0.81, p=0.000; FIG. 16).  
         [0203]    Optical Properties  
         [0204]    Hardwood kraft pulps principally impart optical and surface properties to paper rather than simply strength parameters. FIG. 17 shows the wide range of pulp scattering coefficients obtained from the unbleached clonal pulps at various freeness levels (at 0 PFI rev., the range is 268-363 cm 2 /g). A number of the pulps are exceptional (e.g. 331-1118)—even compared to aspen clones. For the purposes of comparison with the major competitive species, it should be noted that typical eucalypt pulps (Eucalyptus nitens samples) give scattering coefficients over a very similar range, 286-360 cm 2 /g.  
         [0205]    3. Handsheet Analyses—Calcium Accumulation  
         [0206]    It was readily evident from a visual inspection of the resultant sheets that some unusual surface deformations, in the form of raised “bumps” approximately 1 mm in diameter, were prevalent (FIG. 18). The deformations were present in handsheets made after various levels of beating using standard PFI protocols (0-6000 rev.). It could also be observed that these deformations were present to a greater or lesser degree in the sheets dependent on the clonal source of the corresponding pulps. Sheets from the pulps were rated for the numbers of deformations using an arbitrary scale for visual inspection (similar to the ranking system used for assessing pest damage to hybrid poplars in pest-resistance QTL mapping studies. The ratings for each genotype analyzed are tabulated in Table XIV.  
                                           TABLE XIV                           Arbitrary scale rating of degree of surface deformation       accumulation in test handsheets            Genotype   Handsheet Deformation Rating   Number of Clones                    ILL-29   1.5   2        93-968   3   2        53-246   2   2        53-242   3   2       331-1059   2.5   2       331-1061   2   3       331-1062   2.5   2       331-1075   0   1       331-1093   3   2       331-1118   3.5   2       331-1122   2   1       331-1126   0   1       331-1136   4   1       331-1162   3   1       331-1186   3   1                  
 
         [0207]    The results of the MAPMAKER-QTL 1.1 analysis performed using the phenotypic ranking data obtained from handsheet analyses (Table XIII) of each of the poplar clones are presented in Table XV below.  
                                             TABLE XV                           Significant QTL detected for calcium deposition                    LOD       Length/               Trait   Marker/Linkage   Score   Phen %   cM   Weight   Dom.               Calcium   P1150-H07_10/N   2.94   81.7   13.8   0.3286   −1.7214       deposits                  
 
         [0208]    4. Microscopy and X-ray Analysis of Crystalline Deposits  
         [0209]    On further investigation, the deformations were found to be caused by a crystalline deposit found in some vessel elements in the pulp samples used to make the handsheets. These deposits were characterized by SEM/EDS and were found to consist primarily of calcium salts (FIG. 19).  
         [0210]    Examination of wood chips taken from the poplar clones by light microscopy and SEM also revealed the calcium deposits and, more intriguingly, their specific and exclusive nature. FIG. 20 shows an electron micrograph of two adjacent vessel elements in a wood chip, one of which is completely occluded with a deposit. By contrast, the adjacent element is completely free of crystals. Contrary to some literature reports, the deposits seen in this application (as examined microscopically) do not appear to be associated with any form of fungal attack or other decay process.  
         [0211]    Alkaline Peroxide Refiner Mechanical Pulping  
         [0212]    The raw data for the Alkaline Peroxide Refiner Mechanical Pulping (APRMP) from each of 15 hybrid poplar clones consisting of 24 hybrid poplar trees are shown in Table XVI.  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               TABLE XVI                       Properties of APRMP Pulps from Hybrid Poplars                                    14-129 (1)   14-129 (2)                1466-4   1466-3   1466-2   1473-4   1473-3   1473-2               Unscreened CSF (mL)   202   263   378   178   195   259       Specific Energy (MJ/kg)   5.9   5.0   3.9   4.2   3.7   3.1       Screened CSF (mL)   208   274   408   181   206   266       Reject (% o.d. pulp)   0.0   0.0   0.1   0.0   0.0   0.1       Apparent Sheet Density (kg/m 3 )   388   380   350   464   458   439       Burst Index (Kpa · m 2 /g)   2.0   1.8   1.5   2.7   2.6   2.5       Breaking length (km)   4.0   3.8   2.9   5.1   4.8   4.4       Tensile Index (N · m/g)   39.1   36.8   28.4   50.1   47.5   42.8       Stretch (%)   1.57   1.49   1.16   1.97   1.83   1.66       Tear Index (mN · m 2 /g) (4-Ply)   5.5   5.7   5.1   6.1   6.3   6.3       Sheffield Roughness (SU)   137   167   268   105   115   123       Brightness (%)   78   79   79   77   78   78       Opacity (%)   85.5   85.0   84.5   82.4   81.4   81.6       Scattering Coefficient (cm 2 /g)   510   506   503   416   416   418       R - 48 fraction (%)   43.6   46.1   50.0   43.4   43.2   44.6       Fines (P-200) (%)   14.1   13.1   12.0   14.1   13.9   14.2       W. Weighted Average Fibre Length (mm)   1.00   1.06   1.20   0.99   0.97   1.03       L. Weighted Average Fibre Length (mm)   0.78   0.80   0.84   0.78   0.78   0.79       Arithmetic Average Fibre Length (mm)   0.54   0.54   0.54   0.54   0.54   0.54                        53-242 (1)   53-242 (2)                1458-4   1458-3   1458-2   1452-4   1452-3   1452-2               Unscreened CSF (mL)   215   250   373   207   269   380       Specific Energy (MJ/kg)   6.8   6.1   4.9   6.8   5.7   4.4       Screened CSF (mL)   211   275   372   220   262   378       Reject (% o.d. pulp)   0.0   0.0   0.2   0.0   0.0   0.2       Apparent Sheet Density (kg/m 3 )   390   377   359   395   386   364       Burst Index (Kpa · m 2 /g)   2.1   2.0   1.8   2.1   2.0   1.7       Breaking length (km)   3.9   3.5   3.3   4.0   3.7   3.5       Tensile Index (N · m/g)   38.5   34.7   32.5   39.2   36.3   34.1       Stretch (%)   1.67   1.40   1.44   1.52   1.38   1.41       Tear Index (mN · m 2 /g) (4-Ply)   5.7   5.8   6.1   5.3   5.4   5.5       Sheffield Roughness (SU)   133   156   227   126   158   237       Brightness (%)   75   76   76   75   76   76       Opacity (%)   86.5   86.0   85.2   86.9   85.8   85.2       Scattering Coefficient (cm 2 /g)   498   498   489   500   492   482       R - 48 fraction (%)   49.1   49.2   54.1   45.4   47.2   52.5       Fines (P-200) (%)   16.9   17.2   14.1   14.8   14.4   12.5       W. Weighted Average Fibre Length (mm)   1.06   1.08   1.11   0.97   1.00   1.12       L. Weighted Average Fibre Length (mm)   0.84   0.84   0.86   0.77   0.78   0.81       Arithmetic Average Fibre Length (mm)   0.57   0.56   0.57   0.52   0.53   0.54                        53-246 (1)   53-246 (2)                1472-4   1472-3   1472-2   1460-4   1461-3   1461-2               Unscreened CSF (mL)   198   237   372   221   308   388       Specific Energy (MJ/kg)   5.2   4.4   3.2   6.5   5.8   4.5       Screened CSF (mL)   184   236   374   227   326   416       Reject (% o.d. pulp)   0.1   0.1   0.7   0.0   0.1   0.5       Apparent Sheet Density (kg/m 3 )   425   403   382   440   401   374       Burst Index (Kpa · m 2 /g)   2.6   2.4   2.0   2.3   2.1   1.8       Breaking length (km)   4.6   4.3   3.8   4.4   3.8   3.3       Tensile Index (N · m/g)   44.7   42.1   37.1   42.8   37.6   32.1       Stretch (%)   1.89   1.64   1.51   1.99   1.69   1.37       Tear Index (mN · m 2 /g) (4-Ply)   6.8   6.5   6.5   6.2   6.3   6.4       Sheffield Roughness (SU)   117   122   213   110   152   231       Brightness (%)   79   79   79   76   76   77       Opacity (%)   82.5   81.7   81.5   86.8   85.8   85.1       Scattering Coefficient (cm 2 /g)   435   428   427   501   488   473       R - 48 fraction (%)   46.5   48.8   52.5   47.4   50.2   55.4       Fines (P-200) (%)   15.0   13.4   12.2   14.9   15.4   11.3       W. Weighted Average Fibre Length (mm)   1.05   1.11   1.16   1.02   1.15   1.19       L. Weighted Average Fibre Length (mm)   0.81   0.83   0.86   0.82   0.87   0.89       Arithmetic Average Fibre Length (mm)   0.54   0.55   0.55   0.55   0.56   0.56                        93-968 (1)   93-968 (2)                1459-5   1459-4   1459-3   1450-3   1450-2   1451-2               Unscreened CSF (mL)   246   315   382   222   325   382       Specific Energy (MJ/kg)   8.5   7.3   6.1   5.6   4.5   3.8       Screened CSF (mL)   256   304   377   236   344   398       Reject (% o.d. pulp)   0.0   0.1   0.1   0.0   0.1   0.9       Apparent Sheet Density (kg/m 3 )   399   368   361   405   379   357       Burst Index (Kpa · m 2 /g)   2.2   1.9   1.8   2.2   1.9   1.8       Breaking length (km)   4.1   3.7   3.4   4.2   3.5   3.5       Tensile Index (N · m/g)   39.8   36.3   33.1   41.2   34.6   34.3       Stretch (%)   1.82   1.54   1.40   1.51   1.33   1.28       Tear Index (mN · m 2 /g) (4-Ply)   6.1   5.9   6.2   5.9   5.7   5.7       Sheffield Roughness (SU)   127   169   216   124   194   245       Brightness (%)   75   75   76   74   75   75       Opacity (%)   89.1   88.6   87.1   88.1   87.1   85.9       Scattering Coefficient (cm 2 /g)   534   528   510   522   516   487       R - 48 fraction (%)   43.6   51.3   56.5   45.4   50.9   54.5       Fines (P-200) (%)   15.5   13.5   12.6   15.5   14.0   12.5       W. Weighted Average Fibre Length (mm)   1.09   1.15   1.22   1.05   1.09   1.28       L. Weighted Average Fibre Length (mm)   0.87   0.89   0.92   0.81   0.83   0.90       Arithmetic Average Fibre Length (mm)   0.61   0.60   0.61   0.56   0.56   0.58                        331-1059 (2)   331-1059 (3)                1453-3   1457-3   1453-2   1454-3   1455-3   1455-2               Unscreened CSF (mL)   210   249   329   216   239   312       Specific Energy (MJ/kg)   8.9   7.8   7.2   9.1   8.5   7.4       Screened CSF (mL)   230   257   336   212   250   314       Reject (% o.d. pulp)   0.1   0.6   0.8   0.3   0.8   1.9       Apparent Sheet Density (kg/m 3 )   378   363   352   376   350   350       Burst Index (Kpa · m 2 /g)   2.2   2.2   1.9   2.3   2.2   2.0       Breaking length (km)   3.9   3.8   3.5   4.2   4.0   3.7       Tensile Index (N · m/g)   38.5   37.6   33.9   40.9   38.7   36.3       Stretch (%)   1.84   1.70   1.58   2.01   1.89   1.65       Tear Index (mN · m 2 /g) (4-Ply)   5.1   6.3   5.7   6.2   6.3   6.2       Sheffield Roughness (SU)   138   151   181   143   157   187       Brightness (%)   75   75   76   78   78   78       Opacity (%)   88.7   87.4   87.1   87.4   86.5   86.5       Scattering Coefficient (cm 2 /g)   559   518   528   548   537   530       R - 48 fraction (%)   46.8   51.2   51.0   49.2   50.4   53.6       Fines (P-200) (%)   17.1   15.9   16.2   16.6   17.6   14.0       W. Weighted Average Fibre Length (mm)   1.03   1.18   1.14   1.07   1.16   1.20       L. Weighted Average Fibre Length (mm)   0.78   0.82   0.81   0.79   0.81   0.83       Arithmetic Average Fibre Length (mm)   0.51   0.51   0.52   0.52   0.52   0.52                        331-1061 (1)   331-1061 (2)                1476-4   1476-3   1476-2   1474-4   1474-3   1474-2               Unscreened CSF (mL)   169   237   357   194   265   383       Specific Energy (MJ/kg)   5.0   4.0   3.0   6.0   5.1   3.9       Screened CSF (mL)   190   248   380   205   264   375       Reject (% o.d. pulp)   0.0   0.1   0.3   0.0   0.1   0.3       Apparent Sheet Density (kg/m 3 )   426   399   390   386   381   356       Burst Index (Kpa · m 2 /g)   2.7   2.4   2.1   2.2   2.2   1.9       Breaking length (km)   4.9   4.2   3.7   4.5   3.9   3.5       Tensile Index (N · m/g)   48.2   41.0   36.6   44.2   38.4   34.2       Stretch (%)   1.81   1.39   1.40   1.83   1.40   1.32       Tear Index (mN · m 2 /g) (4-Ply)   6.2   5.6   6.1   5.6   5.7   5.7       Sheffield Roughness (SU)   99   130   219   130   156   239       Brightness (%)   76   77   78   76   77   78       Opacity (%)   80.5   80.5   79.8   85.7   84.2   83.8       Scattering Coefficient (cm 2 /g)   387   394   391   482   471   465       R - 48 fraction (%)   48.1   50.2   53.8   46.9   49.3   56.0       Fines (p-200) (%)   15.1   14.9   9.8   14.5   11.9   12.7       W. Weighted Average Fibre Length (mm)   1.07   1.11   1.19   1.06   1.08   1.21       L. Weighted Average Fibre Length (mm)   0.83   0.86   0.89   0.78   0.79   0.84       Arithmetic Average Fibre Length (mm)   0.54   0.56   0.57   0.52   0.53   0.53                        331-1061 (3)   331-1062 (1)                1475-5   1475-4   1475-3   1456-4   1456-3   1456-2               Unscreened CSF (mL)   219   273   363   220   247   361       Specific Energy (MJ/kg)   7.3   6.3   5.1   7.0   6.2   4.9       Screened CSF (mL)   226   301   371   231   270   359       Reject (% o.d. pulp)   0.0   0.1   0.1   0.0   0.1   0.5       Apparent Sheet Density (kg/m 3 )   359   354   336   374   370   349       Burst Index (Kpa · m 2 /g)   1.9   1.7   1.6   1.9   1.9   1.6       Breaking length (km)   3.4   3.3   2.9   3.6   3.4   3.2       Tensile Index (N · m/g)   33.5   31.9   28.2   35.5   33.2   31.4       Stretch (%)   1.25   1.35   1.15   1.43   1.31   1.34       Tear Index (mN · m 2 /g) (4-Ply)   5.0   5.0   4.9   5.5   5.6   5.7       Sheffield Roughness (SU)   168   219   276   132   156   225       Brightness (%)   78   79   80   77   77   77       Opacity (%)   84.9   83.7   83.0   86.2   85.8   84.7       Scattering Coefficient (cm 2 /g)   490   478   466   498   501   482       R - 48 fraction (%)   48.0   54.0   56.1   51.6   53.7   57.2       Fines (P-200) (%)   15.4   13.6   11.4   17.4   17.0   13.5       W. Weighted Average Fibre Length (mm)   1.04   1.06   1.18   1.13   1.22   1.30       L. Weighted Average Fibre Length (mm)   0.82   0.81   0.85   0.87   0.89   0.92       Arithmetic Average Fibre Length (mm)   0.52   0.53   0.53   0.55   0.55   0.56                        331-1062 (2)   331-1075 (2)                1462-4   1462-3   1462-2   1444-4   1444-3   1446               Unscreened CSF (mL)   209   273   351   237   284   411       Specific Energy (MJ/kg)   5.2   4.3   3.5   10.8   9.5   7.9       Screened CSF (mL)   225   289   359   250   297   422       Reject (% o.d. pulp)   0.0   0.0   0.1   0.1   0.1   0.3       Apparent Sheet Density (kg/m 3 )   409   397   386   344   324   309       Burst Index (Kpa · m 2 /g)   2.1   2.1   1.9   1.7   1.6   1.3       Breaking length (km)   4.1   4.1   3.7   3.3   2.8   2.5       Tensile Index (N · m/g)   40.6   40.3   36.3   32.0   27.4   24.8       Stretch (%)   1.39   1.46   1.29   1.36   1.21   1.23       Tear Index (mN · m 2 /g) (4-Ply)   5.4   5.4   5.4   4.8   4.7   4.3       Sheffield Roughness (SU)   116   135   208   182   235   306       Brightness (%)   77   77   78   75   75   76       Opacity (%)   85.4   84.0   83.4   89.3   88.6   88.1       Scattering Coefficient (cm 2 /g)   492   460   458   577   556   549       R - 48 fraction (%)   47.2   48.6   52.9   41.0   46.4   50.0       Fines (P-200) (%)   15.7   15.8   13.1   18.6   17.3   14.2       W. Weighted Average Fibre Length (mm)   1.07   1.15   1.10   0.99   1.07   1.15       L. Weighted Average Fibre Length (mm)   0.83   0.87   0.85   0.78   0.80   0.83       Arithmetic Average Fibre Length (mm)   0.56   0.58   0.56   0.54   0.54   0.54                        331-1093 (1)   331-1093 (2)                1470-4   1470-3   1470-2   1467-4   1467-3   1467-2               Unscreened CSF (mL)   160   200   295   184   210   275       Specific Energy (MJ/kg)   5.7   5.0   4.0   4.6   4.1   3.4       Screened CSF (mL)   171   214   305   192   220   292       Reject (% o.d. pulp)   0.0   0.1   0.4   0.0   0.0   0.1       Apparent Sheet Density (kg/m 3 )   384   381   353   427   424   413       Burst Index (Kpa · m 2 /g)   2.4   2.2   2.0   2.5   2.4   2.1       Breaking length (km)   4.5   4.3   3.8   4.7   4.6   4.1       Tensile Index (N · m/g)   44.5   41.7   36.8   46.3   44.8   40.5       Stretch (%)   1.67   1.55   1.50   1.64   1.63   1.53       Tear Index (mN · m 2 /g) (4-Ply)   5.8   6.1   5.7   5.5   5.6   5.5       Sheffield Roughness (SU)   120   137   186   108   127   159       Brightness (%)   74   75   76   79   78   79       Opacity (%)   86.5   86.3   85.8   84.4   83.8   84.0       Scattering Coefficient (cm 2 /g)   522   506   506   493   484   495       R - 48 fraction (%)   44.2   46.4   49.6   39.0   42.0   45.3       Fines (P-200) (%)   16.6   14.8   13.2   15.6   13.4   11.4       W. Weighted Average Fibre Length (mm)   1.04   1.06   1.21   0.96   0.97   1.00       L. Weighted Average Fibre Length (mm)   0.74   0.75   0.79   0.73   0.73   0.74       Arithmetic Average Fibre Length (mm)   0.51   0.51   0.52   0.52   0.52   0.52                        331-1118 (1)   331-1118 (2)                1468-3   1468-2   1469-2   1471-4   1471-3   1471-2               Unscreened CSF (mL)   149   191   283   184   223   358       Specific Energy (MJ/kg)   4.2   3.8   3.0   6.5   5.5   4.3       Screened CSF (mL)   159   200   296   197   240   383       Reject (% o.d. pulp)   0.0   0.0   0.4   0.0   0.0   0.3       Apparent Sheet Density (kg/m 3 )   463   458   393   376   358   340       Burst Index (Kpa · m 2 /g)   2.9   2.8   2.2   2.2   2.0   1.7       Breaking length (km)   5.3   5.0   4.3   4.1   3.6   3.1       Tensile Index (N · m/g)   51.7   49.5   41.7   40.2   35.1   30.7       Stretch (%)   1.90   1.83   1.65   1.69   1.41   1.25       Tear Index (mN · m 2 /g) (4-Ply)   6.0   6.0   6.3   5.6   5.6   6.1       Sheffield Roughness (SU)   103   113   161   135   164   264       Brightness (%)   77   78   78   77   77   78       Opacity (%)   83.3   82.0   82.3   86.2   86.2   85.3       Scattering Coefficient (cm 2 /g)   431   429   439   508   520   496       R - 48 fraction (%)   40.5   40.8   47.6   42.3   45.7   48.5       Fines (P-200) (%)   13.7   13.6   12.1   17.2   15.0   14.3       W. Weighted Average Fibre Length (mm)   0.97   0.96   1.11   1.01   1.07   1.15       L. Weighted Average Fibre Length (mm)   0.74   0.74   0.78   0.77   0.78   0.80       Arithmetic Average Fibre Length (mm)   0.52   0.52   0.53   0.53   0.53   0.54                        331-1122 (1)   331-1126 (1)                1447-4   1447-3   1448-2   1465-4   1465-3   1465-2               Unscreened CSF (mL)   210   300   425   191   255   379       Specific Energy (MJ/kg)   7.3   6.1   4.3   6.3   5.2   4.0       Screened CSF (mL)   227   313   420   202   267   403       Reject (% o.d. pulp)   0.1   0.2   0.7   0.0   0.0   0.2       Apparent Sheet Density (kg/m 3 )   360   339   327   363   345   320       Burst Index (Kpa · m 2 /g)   1.7   1.6   1.4   1.8   1.7   1.4       Breaking length (km)   3.6   3.3   2.8   3.5   3.3   2.8       Tensile Index (N · m/g)   35.8   31.9   27.2   34.8   31.9   27.1       Stretch (%)   1.33   1.37   1.11   1.45   1.40   1.25       Tear Index (mN · m 2 /g) (4-Ply)   4.0   3.9   3.8   4.8   5.0   5.0       Sheffield Roughness (SU)   144   220   290   164   221   304       Brightness (%)   75   75   76   75   75   76       Opacity (%)   88.0   87.2   86.3   86.3   86.2   85.2       Scattering Coefficient (cm 2 /g)   533   518   506   505   497   480       R - 48 fraction (%)   45.6   54.1   56.0   44.3   48.6   52.1       Fines (P-200) (%)   15.8   14.0   11.3   20.3   15.8   14.9       W. Weighted Average Fibre Length (mm)   1.00   1.06   1.25   1.08   1.10   1.24       L. Weighted Average Fibre Length (mm)   0.75   0.78   0.84   0.85   0.87   0.90       Arithmetic Average Fibre Length (mm)   0.49   0.52   0.52   0.58   0.58   0.59                        331-1162 (3)   331-1186 (3)                1464-4   1464-3   1464-2   1449-4   1449-3   1449-2               Unscreened CSF (mL)   170   215   266   188   253   380       Specific Energy (MJ/kg)   5.4   4.8   4.0   7.6   6.5   5.1       Screened CSF (mL)   197   232   291   212   269   382       Reject (% o.d. pulp)   0.0   0.0   0.1   0.0   0.0   0.1       Apparent Sheet Density (kg/m 3 )   417   400   394   409   402   354       Burst Index (Kpa · m 2 /g)   1.9   1.8   1.8   2.4   2.1   1.7       Breaking length (km)   3.7   3.6   3.3   4.3   3.8   3.4       Tensile Index (N · m/g)   36.5   35.5   32.8   42.0   37.4   32.9       Stretch (%)   1.36   1.38   1.17   1.74   1.44   1.36       Tear Index (mN · m 2 /g) (4-Ply)   5.0   5.1   4.5   5.8   5.6   5.6       Sheffield Roughness (SU)   115   136   163   104   142   226       Brightness (%)   74   74   74   76   77   78       Opacity (%)   88.5   87.9   87.1   86.2   85.6   84.8       Scattering Coefficient (cm 2 /g)   530   514   518   505   500   499       R - 48 fraction (%)   45.3   45.4   46.5   46.4   48.7   51.6       Fines (P-200) (%)   19.5   14.1   14.1   16.0   16.1   14.6       W. Weighted Average Fibre Length (mm)   1.06   1.10   1.06   1.00   1.04   1.12       L. Weighted Average Fibre Length (mm)   0.84   0.86   0.84   0.79   0.80   0.83       Arithmetic Average Fibre Length (mm)   0.57   0.57   0.57   0.52   0.52   0.53                  
 
         [0213]    In general, appropriate baseline values of pulp freeness and specific refining energy are the two parameters commonly used to monitor mechanical and optical properties of APRMP pulps. Thus, to facilitate data analysis and discussion, the raw data were standardized by interpolation or extrapolation to a freeness of 200 mL CSF (Table XVII) and a specific refining energy (SRE) of 6.0 MJ/kg (Table XVIII).  
                                                                                                                           TABLE XVII                           Properties of APRMP Pulps from Hybrid Poplars at a Constant Freeness of 200 mL CSF                            Length                                           Specific           Weighted           Refining   R - 48   Fines   Fiber   Sheet   Tensile           Bright-   Sheffield   Scattering           Energy   Fraction   (P-200)   Length   Density   Index   Stretch   Tear Index   ness   Roughness   Coefficient   Opacity       Hybrid No.   (MJ/kg)   (%)   (%)   (mm)   (kg/m 3 )   (N · m/g)   (%)   (mN · m 2 /g)   (%)   (SU)   (cm 2 /g)   (%)                    14-129 (1)   5.9   43.5   14.0   0.78   392   40.0   1.60   5.5   78   130   510   85.5       14-129 (2)   3.7   43.2   13.9   0.78   459   48.2   1.87   6.3   78   111   416   81.9       53-242 (1)   7.0   48.0   17.4   0.81   392   39.0   1.68   5.7   75   128   498   86.6       53-242 (2)   6.9   44.5   15.2   0.77   399   40.0   1.54   5.3   75   113   503   87.3       53-246 (1)   5.2   47.3   14.5   0.81   417   43.8   1.80   6.7   79   118   432   82.2       53-246 (2)   6.7   46.5   15.8   0.82   448   44.5   2.09   6.2   76   95   506   87.0       93-968 (1)   9.3   40.0   17.4   0.85   413   42.5   1.94   6.1   75   90   547   90.1       93-968 (2)   5.9   43.3   16.3   0.79   417   42.5   1.56   5.9   74   95   528   88.7       331-1059 (2)   9.1   45.0   17.5   0.79   383   40.0   1.90   5.0   75   127   565   88.8       331-1059 (3)   9.3   48.5   17.0   0.79   383   41.2   2.06   6.2   78   137   550   87.4       331-1061 (1)   4.6   48.6   15.1   0.84   417   46.0   1.75   6.2   76   103   389   80.5       331-1061 (2)   5.9   46.8   14.5   0.78   389   44.5   1.83   5.6   76   127   482   85.7       331-1061 (3)   7.5   47.4   16.2   0.80   361   34.8   1.30   5.0   78   150   494   85.4       331-1062 (1)   7.2   50.4   18.3   0.87   382   37.0   1.48   5.5   77   107   504   86.6       331-1062 (2)   5.3   46.5   16.7   0.84   413   42.0   1.50   5.4   77   105   490   85.6       331-1075 (2)   11.1   38.0   19.8   0.77   361   34.0   1.40   5.0   75   155   580   89.5       331-1093 (1)   5.0   45.6   15.7   0.75   382   42.7   1.59   6.0   75   132   511   86.4       331-1093 (2)   4.3   40.0   14.8   0.73   426   45.9   1.64   5.5   79   114   490   84.2       331-1118 (1)   3.7   40.8   13.6   0.75   448   49.5   1.83   6.0   78   113   429   82.0       331-1118 (2)   6.0   42.5   17.2   0.77   376   40.2   1.69   5.6   77   137   508   86.2       331-1122 (1)   7.5   43.8   16.5   0.74   368   37.0   1.45   4.0   75   128   536   88.2       331-1126 (1)   6.1   44.3   20.3   0.85   363   34.8   1.45   4.8   75   164   505   86.3       331-1162 (3)   5.0   45.3   19.5   0.85   415   36.5   1.36   5.0   74   115   530   88.5       331-1186 (3)   7.3   46.3   16.1   0.79   415   43.0   1.78   5.8   76   94   505   86.3                  
 
         [0214]    Specific Refining Energy  
         [0215]    The specific refining energy consumed to reach a given freeness in the range of 150 to 425 mL CSF for the 24 hybrid poplar trees is shown in FIG. 21. The raw data show considerable scatter thanks largely to intraclonal variability which renders clonal effects non-significant (ANOVA p=0.067). Each set of points in FIG. 21 is surrounded by envelopes rather than a best-fit line or curve. The envelopes can be classified into three general groups as shown below.  
                                                       High SRE Group   Medium SRE Group   Low SRE Group                            93-968(1)    14-129(1)    14-129(2)           331-1059(2)    53-242(1)    53-246(1)           331-1059(3)    53-242(2)   331-1061(1)           331-1075(2)    53-246(2)   331-1062(2)                93-968(2)   331-1093(1)               331-1061(2)   331-1093(2)               331-1061(3)   331-1118(1)               331-1062(1)   331-1162(3)               331-1118(2)               331-1122(1)               331-1126(1)               331-1186(3)                      
 
         [0216]    The differences in SRE demand are more evident at 200 mL CSF as clones 93-968(1) and 331-1059(3) require 9.3 MJ/kg SRE whereas clones 14-129(2) and 331-1118(1) require 3.7 MJ/kg SRE or 60% of the energy demand (Table XVII). Clone 331-1075(2) is clearly exceptional as it required 11.1 MJ/kg of specific refining energy to the same freeness level. The three distinct SRE groups shown in FIG. 21 are consistent with previous observations of chemithermomechanical (CTMP) pulping of nine different “wild” aspen clones from Northeast British Columbia.  
         [0217]    NaOH/H 2 O 2  uptake for each tree are shown in Table XIX. The data indicate a much lower chemical uptake for the unusual high energy consumption clone 331-1075(2) than for the other clones investigated in this study. NaOH uptake values for each clone at 200 mL CSF are plotted against SRE in FIG. 22. FIG. 22 shows that high chemical uptake reduces energy demand at a given freeness of 200 mL. The significant negative relationship noted here (Pearson coefficient −0.526, p=0.025) agrees well with previous findings that SRE of hardwood mechanical pulps increases with diminishing chemical uptake, although the variability seen here is greater than that observed for aspen CTMP pulps. The reasons for intraclonal variability in chemical uptake are not clear. The most probable explanation for low chemical uptake by certain clones is likely a function of the cell wall thickness and lumen diameters of earlywood (large) and latewood (small). It has been reported that a thicker S1 wall makes it more difficult for the hardwood fiber to absorb chemical in order to swell and/or collapse. A plot of the NaOH uptake vs. chip density (FIG. 23) also confirms previous observations that wood density does not affect chemical uptake by Populus species chips and further contrasts with data suggesting that earlywood density affects chemical uptake for Eucalyptus nitens.  
                                                   TABLE XIX                           Chip density and chemical uptake for APRMP pulps       Chip thickness = 2-6 mm                Chip Density a     NaOH   H 2 O 2         Sample No.   (kg/m 3 )   (% o.d. wood)   (% o.d. wood)                     14-129 (1)   285   5.39   3.44        14-129 (2)   304   6.07   3.88        53-242 (1)   329   5.13   3.27        53-242 (2)   302   4.41   2.82        53-246 (1)   311   6.24   3.99        54-246 (2)   325   4.57   2.92        93-968 (1)   303   4.20   2.68        93-968 (2)   314   3.80   2.43       331-1059 (2)   303   4.63   2.95       331-1059 (3)   302   4.59   2.93       331-1061 (1)   338   6.40   4.09       331-1061 (2)   328   5.41   3.46       331-1061 (3)   345   4.35   2.78       331-1062 (1)   280   4.20   2.68       331-1062 (2)   290   6.51   4.24       331-1075 (2)   300   3.39   2.16       331-1093 (1)   279   4.23   2.70       331-1093 (2)   288   5.38   3.43       331-1118 (1)   346   5.89   3.76       331-1118 (2)   373   3.42   2.18       331-1122 (1)   283   3.80   2.43       331-1126 (1)   386   2.69   1.72       331-1162 (3)   336   4.22   2.69       331-1186 (3)   292   4.69   3.00                  
 
         [0218]    Fiber Properties  
         [0219]    As expected, the long-fiber fraction R-48 (retained on the 48-mesh screen of a Bauer-McNett fiber classifier) and LWFL (length-weighted fiber length) increased with increasing freeness and decreasing SRE, whereas the fines content P-200 (passed through the 200-mesh screen of a Bauer McNett fiber classifier) increased with decreasing freeness and increasing SRE as shown in Table XVII. The LWFL values obtained from the mechanical APRMP pulps at a freeness of 200 mL (Table XVII) show a significant correlation (Pearson coefficient 0.479, p=0.018) with the LWFL values observed for the chemical pulps (Table XI) obtained from the same clones. Unexpectedly, the LWFL values for APRMP pulps were consistently longer than those from the chemical pulps obtained from the same trees. The reasons for this observation is not clear. Perhaps, the alkali treatment of hybrid poplar have softened the middle lamella thus allowing the individual fibers to be peeled from the matrix in a longer and a more intact state in the refiner than those from the chemical pulping process.  
         [0220]    Strength Properties and Sheet Consolidation  
         [0221]    Tensile index increased with decreasing freeness, increasing sheet density, and increasing specific refining energy (Table XVI). In addition, LWFL also has a highly significant negative relationship with APRMP pulp tensile index (Pearson coefficient −0.74, p=0.001). In general, there is considerable variability in tensile strength from the various clones at a given freeness of 200 mL CSF and a given specific refining energy of 6.0 MJ/kg (Tables XVII and XVIII, respectively). At a given freeness of 200 mL CSF the tensile index values range from 34.0 to 49.5 N·m/g. There is also considerable interclonal variability in tensile strength, for example, the three individuals comprising the genotype clone 331-1061 have a mean tensile index of 41.8 N·m/g with a standard deviation of 5.0 N·m/g at a given freeness of 200 mL CSF (Table XVII). In FIG. 24, NaOH uptake is plotted against tensile index. Again, the data are variable, but it is clear that despite this at a given freeness, increasing chemical uptake results in an increase in tensile strength (Pearson coefficient 0.700, p=0.022). This finding is in good agreement with previous work by Johal et al. and Jackson et al. who found that the tensile indices of aspen CTMP pulps increase with increasing chemical uptake. Intraclonal variation is again the largest component of the variability seen in the tear index data at a given freeness of 200 mL CSF (Table XVII).  
         [0222]    As anticipated, sheet density increases with decreasing freeness and increasing specific refining energy (Table XVII). The extent of the intra- and interclonal variability seen at 200 mL freeness, from 361 kg/M 3  to 459 kg/M 3 , is of the same order as that previously noted for aspen clones and is shown in Table XVII. Whilst some clones (e.g. parent 93-968) produce sheets with similar density properties, others (e.g. parent 14-129) exhibit wide intraclonal variability. The role of alkali uptake at 200 mL freeness in the consolidation of sheet density of hybrid poplar clone APRMP pulps is shown in FIG. 25. The significant positive relationship seen (Pearson coefficient 0.616, p=0.001) indicates the importance of good chemical impregnation to soften fiber cell walls and improve sheet consolidation.  
         [0223]    Surface and Optical Properties  
         [0224]    As expected, scattering coefficient consistently increased with decreasing freeness and increasing sheet density (Table XVII). Significant positive correlations were observed between SRE and optical properties scattering coefficient (Pearson coefficient 0.779, p=0.000) and printing opacity (Pearson coefficient 0.738, p=0.003).  
         [0225]    In FIG. 26, the fines content (P-200) is shown as a function of scattering coefficient. The significant positive relationship (Pearson coefficient 0.637, p=0.001) confirms previous observations for aspen in that those clones with the highest fines content also exhibit high scattering coefficients and high opacity values. The negative effect of chip alkali uptake—on light scattering development is indicated in FIG. 27 (Pearson coefficient −0.713, p=0.000). The most probable explanation for this negative effect is that increased alkali uptake makes the fiber separation at the middle lamella easier and thus producing fewer fines. Secondly, the higher alkali uptake makes the fibers more flexible and hydrophilic thus resulting in more fiber bonding and reduced light scattering.  
         [0226]    Sheffield roughness increased with increasing freeness (FIG. 28). The plot of Sheffield roughness vs. tensile strength (FIG. 29) indicates that at high tensile index, most clones exhibit excellent sheet surface properties. The significant negative relationship seen (Pearson coefficient −0.602, p=0.002) does not alter the fact that, within this hybrid population, a wide variety of pulp strengths can be had whilst maintaining a constant smoothness level (see Table XX).  
                                           TABLE XX                           Interclonal variability of strength properties for       given formation properties            Clone   Tensile index (N · m/g)   Sheffield Smoothness (SU)                    331-1118 (1)   49.5   113       331-1162 (3)   36.5   115                  
 
         [0227]    The brightness of the APRMP pulps from different clones under significantly variable H 2 O 2  uptake was surprisingly similar. A tight range of brightness values was obtained from the hybrid poplar pulps, from 74-79%. This compares very well with previous brightness results for aspen clones which showed greater variability over a lower spectrum of values, from 49-69%. The aspen values may be explained by the occurrence in natural stands of highly stained wood and by wide differences in the lignin content of the examined trees.  
         [0228]    QTL Mapping Using Pulp Properties Phenotypic Data  
         [0229]    For most of the pulping parameters examined in this study, both intra- and interclonal factors were significant determinators of the population variability encountered. This, coupled with the necessarily small sample size utilized, makes the correlation of genotypic and phenotypic variability statistically challenging. Some data sets did yield significant QTL detections—for example, a putative QTL has been found for H-factor with a LOD score of 4.04 (see FIG. 30 and Table XXI). In FIG. 30, the 19 Populus linkage groups and positioned RFLP, RAPD and STS markers are shown. Positions of detected QTL which exceed the significance threshold LOD score are indicated by colour-coded vertical bars adjacent to the linkage groups. Phenotyping data colour codes are described in the legend. Importantly using the kraft pulping data, a significant QTL for tensile index (LOD score 3.48) and a less significant QTL for air resistance (LOD score 2.62) were detected in a chromosomal position coincident with that detected for fiber coarseness and microfibril angle. These results are depicted in Table XXI. These data suggest that not only does this genetic region contain genes which affect multiple related pulp parameters and is therefore worthy of further investigation, but that the coarseness values obtained from the peracetic acid maceration/FQA fiber analysis technique do indeed accurately reflect the performance of the pulp in terms of a number of important parameters. The observation strongly supports the use of this procedure as a technique for rapid assessment of tree populations for wood quality.  
         [0230]    Most of the QTL found, however, had LOD significance scores of approximately the threshold value of 2.90 or lower, indicating a high possibility of spurious detection. QTL mapping of these data is, therefore, not presented here as the data sets are simply not extensive enough for statistical significance. These data will form part of a larger and continuing study on this population of hybrid poplars with the eventual goal of genetic mapping of specific pulping and papermaking characteristics. This is considered to be an important outcome as, as has been clearly shown by this and numerous other reports, it is often highly problematic to accurately predict pulp and papermaking properties from easily measured parameters such as fiber properties, wood density, etc. To actually determine the pulp and paper properties of a clone, it is still necessary to pilot pulp the entire stem. It is anticipated that QTL mapping of a large enough sample set of pilot pulps will enable the detection of the particular subset of genes which directly affect pulp and paper parameters and the development of rapid assessment methods for those properties of immediate industrial value. This study represents the first steps towards eventual achievement of this highly important objective.  
                                                                           TABLE XXI                           Significant QTL detected for H factor            Trait   Marker/Linkage   LOD Score   Phen %   Length/cM   Weight   Dom.                    H factor   PAL2-P214/Y   4.04   95.6   6.6   169.83   −337.80       Tensile index   I14_09-F15_10/E   3.48   87.2   37.3   1.5378   9.8668       Air resistance   I14_09-F15_10/E   2.62*   88.4   37.3   519.36   −250.13       (Gurley)       Fiber   I14_09-F15_10/E   3.49   55.9   37.3   72.794   −79.906       Coarseness**                                  
 
         [0231]    QTL Mapping  
         [0232]    [0232]FIG. 30 illustrates the current status of QTL mapping using the Family 331 hybrid poplar mapping pedigree. The map shows the 19 linkage groups that are approximately equivalent to the 19 Populus chromosomes as vertical bars labelled A-Y as obtained from the University of Washington. Positions of assigned RFLP, RAPD and STS markers are indicated on each linkage group. Assigned QTL regions for each of the traits examined in the study are indicated as colour-coded bars adjacent to the linkage groups. Details on the significance of the QTL and the genetic distances they cover can be found in the appropriate tables, although it is important to note that—with the single exception of kraft pulp yield—each reported QTL exceeds the 95% statistical confidence level, as determined by the LOD threshold score of 2.9.  
         [0233]    RAPD Analysis and Polymorphic Product Characterization  
         [0234]    Table XVI shows the screened suite of markers associated with the QTL linked to the specific traits of interest examined in this study. Each of these RAPD/RFLP markers was used in a PCR reaction to generate a polymorphic product from the phenotypically selected F2 generation individuals indicated. Table XVI also presents the number of sequences generated from the polymorphic bands isolated. Proposed functionalities for the sequences, based on similarities to sequences already in public databases, can be found in Table XVI. The sequences are tabulated in Table XVII. The polymorphic marker bands have been fully or partially sequenced and functionality has been assigned according to similarity with previously published sequences on public databases (e.g. genbank).  
         [0235]    By sequence homology it will now be possible to identify orthologous functional genes in trees of the genus Populus, Picea, Berula, Abies, Larix, Taxus, Ulmus, Prunus, Quercus, malus, Arbutus, Salix, Platanus, Acer, Tsuga, Pseudotsuga, Pinus, Fraxinus, Eucalyptus, Acacia, Abrus, Cupressus, Fagus, Juniperus, Thuja and Canya.  
                                                       #   Product size           Trait   Marker   Sequences   (bp)   Database ID                   Maceration   I17_04   2       (AC007018)  Arabidopsis thaliana         yield               chromosome;                       (AP002820) putative transposable                       element Tip 100 protein RICE       Maceration   G02_11   5   1138, 990,   (AC006136) putative retroelement       yield           1032, 976, 986   pol polyprotein [Arabidopsis]                       (AC009400) hypothetical protein                       [ Arabidopsis thaliana ;                       &gt;gi|13241678|gb|AAK16420.1|                       (AF320086) RIRE gag/pol protein                       [ Zea mays ]; unknown; AC020580)                       hypothetical protein, 3&#39;partial       Yield/H   E01_04   3   347, 334, 356   (AC002332) hypothetical protein       factor               [ Arabidopsis thaliana ]; AC007357)                       F3F19.15 [ Arabidopsis thaliana ];                       (AB024037)                       emb|CAB77928.1˜gene_id: MSK1                       0.2˜similar to unknown       Yield/H-   P1027   3   539, 589, 593   hypothetical protein, At; putative       factor               retroelement; At EST ATTS1136,                       putative disease resistance gene.       Lignin   P757   2   281, 199   Arabidopsis retrotransposon-like                       protein, Z97342.       Coarseness/   I14_09   3   545, 545, 869   unknown;       tensile               low hits: cotton fad aj244890;       index/air               poplar agamous (64% in 197 nt);       resistance               copia-like polyprotein [ Arabidopsis                           thaliana ]           F15_10   2   950, 980   unknown Arabidopsis gene;                       Many proline-rich proteins (#1 =                       cicer arietinium), +3 frame       Extractives   B15   2   1756, 1693   endo-1,4-betaglucanase,                       fibronectin repeat signature           H19_08   1   810   transformer-SR ribonucleoprotein           G13_17   2   1400, 1628   several dnaJ-like protein                       [ Arabidopsis thaliana ];                       gi|1491720|emb|CAA67813.1|                       (X99451) extensin-like protein                       Dif10 [Lycopersicon esculentum           G12_15   1   677   1 = unknown At protein,                       2 = hypothetical Ca-binding                       protein from At           C04_04   1   357   genomic DNA T7N9.15                       [ Arabidopsis thaliana ]           P1054   1   787   Cicer arietinum mRNA for glucan-                       endo-1,3-beta-glucosidase           P1018   1   522   AC007197  Arabidopsis thaliana                         chromosome           H12   3   332, 386, 350   hypothetical protein (COP1                       regulatory), endoglucanase,                       3-oxo-5-alpha-steroid-4-                       dehydrogenase.       Calcium   H07_10   3   977, 978, 754   (AC003970) Similar to Glucose-6-       deposition               phosphate dehydrogenases, At;                       AC006267) putative polyprotein                       [ Arabidopsis thaliana ];                       (AC006267) putative polyprotein                       [ Arabidopsis thaliana ]                  
 
         [0236]    While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.