bluuebunny/crossref_metadata_2025 huggingface dataset:
Agronomic Performance of Transgenic Burley Tobaccos Expressing TVMV or AMV Coat Protein Genes with and without Virus Challenges
Authors: Xu Dongmei , Collins Glenn B. , Hunt Arthur G. , Nielsen Mark T.
Published: July 2010

Eighty transgenic tobacco (Nicotiana tabacum L.) lines expressing either the tobacco vein mottling virus (TVMV) coat protein (CP) gene or the alfalfa mosaic virus (AMV) CP gene were evaluated for their agronomic performance with or without virus challenge. AH TVMV CP lines were characterized previously for their virus resistance following challenge with three different potyviruses. In the absence of virus challenge, the cured leaf yield of more than 80% of the TVMV CP lines was not significantly different from their nontransgenic counterparts; half of the poor performing lines were in one of the five genetic backgrounds. Similarly, most of the negative variation for yield among the AMV CP transgenic lines was within a single genetic background. Variation for other agronomic traits, including plant height, leaf size, and stalk diameter closely followed the results for yield. Following virus challenge, cured leaf yield of the most resistant transgenic lines was similar to the non‐challenged treatment. Among the AMV CP transgenic lines, yield loss following challenge with AMV was reduced from 22 to 30%. These results suggest that the primary selection criterion in a population of transgenic tobacco lines containing a viral CP gene should be for virus resistance, but it must be recognized that variation for agronomic performance may exist among the resistant selections, particularly in some genetic backgrounds.
Isozyme Variation within and among Accessions of Annual Phalaris Species in North American Germplasm Collections
Authors: Matus Maria , Hucl Pierre
Published: July 2010

Accessions of annual Phalaris species in germplasm collections lack adequate genetic characterization for utilization. The objective of this study was to assess the level of isozyme variability of five annual Phalaris species, including 49 annual canarygrass (P. canariensis L.; 2n = 2x = 12), 24 P. brachystachys Link. (2n = 2x = 12), 48 P. minor Retz. (2n = 4x = 28), 19 P. paradoxa L. (2n = 2x = 14), and P. angusta Nees ex Tris (2n = 2x = 14) accessions from North American germplasm collections. Eight enzymes were used to detect polymorphism within and among accessions by scoring the presence or absence of 62 bands. Polymorphism was detected in 6 of 19 bands in P. canariensis, 12 of 22 bands in P. brachystachys, 34 of 40 bands in P. minor, 19 of 29 bands in P. paradoxa, and 6 of 21 bands in P. angusta. Polymorphism was detected in 23 accessions (47%) P. canariensis, 15 accessions (63%) of P. brachystachys, 35 accessions (73%) of P. minor, four accessions (19%) of P. paradoxa and three accessions of P. angusta (100%). Within‐accession polymorphic indices ranged from 0 to 0.03 in P. canariensis, 0 to 0.02 in P. brachystachys, 0 to 0.06 in P. minor, 0 to 0.04 in P. paradoxa, and 0.01 to 0.04 in P. angusta. Jaccard's similarity coefficients ranged from 0.83 to 1.0 in P. canariensis, 0.78 to 1.0 in P. brachystachys, 0.47 to 1.0 in P. minor, 0.44 to 1.0 in P. paradoxa, and 0.81 to 0.86 in P. angusta. Little isozyme variation existed either within or among accessions of the four diploid species. Phalaris minor, an autotetraploid, possessed greater variation among accessions rather than within accessions. In summary, limited variation was detected by means of isozymes in these five annual Phalaris species obtained from North American germplasm collections.
Variance Effective Population Size under Mixed Self and Random Mating with Applications to Genetic Conservation of Species
Authors: Vencovsky Roland , Crossa José
Published: July 2010

When collecting and regenerating genetic resources, genetic drift affects the representation of a population and occurs at two stages: when sampling the parents and when gametes are sampled from these parents. The variance effective population size [Ne(v)] quantifies genetic drift. In this study, a model for calculating Ne(v), that considers the two‐stage sampling of mixed self and random mating species, is developed. For germplasm collection, as the rate of natural or artificial self‐fertilization (s) increases, Ne(v) is reduced and becomes increasingly dependent on the number of seed parents (P) and is less influenced by the number of seeds sampled per parent (n/P). Female gametic control (GC) leads to higher Ne(v) than with random sampling of seeds (RS), but its effect is tangible only when n/P is small. For accession regeneration, maintaining accession integrity (the proportion of functional parents, u) at an adequately high level and adopting GC are required for assuring Ne(v) equal to or greater than the actual size of the accession (Ne(v) ≥ n). The importance of these two factors is enhanced as s increases. For arbitrary rates of selfing (0 ≤ s ≤ 1), under inbreeding equilibrium (IE) and with constant population size (n = N), Ne(v) can be adequately maintained through GC with a loss of ≤20% within accessions. For large sample size (n → ∞), an accession loss of ≤33% can be recovered. For maintaining adequate Ne(v), artificial selfing followed by GC is more efficient than accession regeneration by natural reproduction. For achieving appropriate Ne(v)s, increasing the rate of self‐fertilization in polymorphic materials makes collection more difficult but regeneration easier for minimal loss (≤20%) within accessions.
Comparison of Selection Strategies for Marker‐Assisted Backcrossing of a Gene
Authors: Frisch Matthias , Bohn Martin , Melchinger Albrecht E.
Published: July 2010

Marker‐assisted selection can accelerate recovery of the recurrent parent genome (RPG) in backcross breeding. In this study, we used computer simulations to compare selection strategies with regard to (i) the proportion of the RPG recovered and (ii) the number of marker data points (MDP) required in a backcross program designed for introgression of one target allele from a donor line into a recipient line. Simulations were performed with a published maize (Zea mays L.) genetic map consisting of 80 markers. Selection for the target allele was based on phenotypic evaluation. In comparison to a constant population size across all generations, increasing population sizes from generation BC1 to BC3 reduced the number of required MDP by as much as 50% without affecting the proportion of the RPG. A four‐stage selection approach, emphasizing in the first generations selection for recombinants on the carrier chromosome of the target allele, reduced the required number of MDP by as much as 75% in comparison to a selection index taking into account all markers across the genome. Adopting the above principles for the design of marker‐assisted backcross programs resulted in substantial savings in the number of MDP required.
Selection Improves Drought Tolerance in Tropical Maize Populations: I. Gains in Biomass, Grain Yield, and Harvest Index
Authors: Edmeades G.O. , Bolaños J. , Chapman S.C. , Lafitte H.R. , Bänziger M.
Published: July 2010

Drought is common in tropical environments, and selection for drought tolerance is one way of reducing the impacts of water deficit on crop yield. The primary objective of this study was to evaluate biomass, grain yield, and harvest index of maize (Zea mays L.) populations selected for drought tolerance. Three late‐maturing tropical maize populations were subjected to three cycles of S1 recurrent selection (‘La Posta Sequía’ and ‘Pool 26 Sequıa’ ) or eight cycles of full‐sib recurrent selection (‘Tuxpeño Sequía’) for yield and traits indicative of drought tolerance during flowering and grain filling. Selection gains were assessed in five trials conducted under mid–late season drought and in five trials conducted under well‐watered conditions. In water‐stressed environments, with average yields of 1.0 to 4.5 Mg ha−1, yield gains averaged 0.26 Mg ha−1 (12.6%) cycle−1 for La Posta Sequía and Pool 26 Sequía and 0.08 Mg ha−1 (3.8%) cycle−1 for Tuxpeño Sequía. In well‐watered conditions, where mean yields ranged from 5.8 to 10.4 Mg ha−1, corresponding gains per cycle were 0.12 Mg ha−1 (1.5%) and 0.04 Mg ha−1 (0.5%). Total biomass was unaffected by selection. Mean correlated responses to selection observed under drought were −0.11 Mg ha−1 cycle−1 in stem biomass and 0.025 cycle−1 in harvest index (HI), and under well‐watered conditions, 0.005 cycle−1 in HI. Stem biomass and HI were negatively correlated under drought Improved drought tolerance was attributed to simultaneous selection in well‐watered environments and under carefully managed water stress at flowering, resulting in greater partitioning of biomass to the ear and increased harvest index.
Selection Improves Drought Tolerance in Tropical Maize Populations: II. Direct and Correlated Responses among Secondary Traits
Authors: Chapman S.C. , Edmeades G.O.
Published: July 2010

Recurrent selection for drought tolerance for three to eight cycles has increased grain yield (GY) under drought at flowering by 30 to 50% in three lowland tropical maize (Zea mays L.) populations. The relationships among secondary traits as a result of this selection have not been determined, however. The objectives of this study were to measure direct and correlated changes due to selection in secondary traits by evaluating cycles of selection and appropriate check entries at five water‐stressed (mean yield 2.35, range 1.01–4.48 Mg ha−1) and five well‐watered environments (mean yield 7.96, range 5.81–10.40 Mg ha−1). Under drought, changes per cycle with recurrent S1 selection (P < 0.05) were as follows: GY 12.6%, fertile ears per plant (EPP) 8.9%, grains per fertile ear (GPE) 6.3%, grain number per square meter 12.2%, 1000 grain weight no change, anthesis‐silking interval (ASI) −22.0%, days from sowing to 50% anthesis −0.7%, plant height −2.0%, primary tassel branch number −5.9%, and senesced leaf area 2.7%. Responses under well‐watered conditions were smaller but generally of the same sign. Grain yield was strongly associated with grain number per square meter in both water‐stressed and well‐watered environments Grain yield, EPP, and GPE were strongly correlated with ASI across entries under drought , though not when water was plentiful. The use of managed stress environments that consistently reveal genetic variation for these traits at specific times during crop development is endorsed for selection purposes.
Limitation to Photosynthesis in Pratylenchus penetrans‐ and Verticillium dahliae‐Infected Potato
Authors: Saeed I.A.M. , MacGuidwin A.E. , Rouse D.I. , Sharkey T.D.
Published: July 2010

Mechanism(s) responsible for decrease in photosynthetic rates of potato (Solanum tuberosum L.) leaves infected by the fungus Verticillium dahliae (Kleb) and the nematode Pratylenchus penetrans (Cobb, Sher, Allen) have not been fully researched. Two growth chamber experiments were undertaken to determine the factors contributing to the decrease in CO2 exchange rates of young, fully expanded leaflets of potato (cv. Russet Burbank) plants grown in pots infested with P. penetrans and/or V. dahliae Treatments were P. penetrans‐infested soil, V. dahliae‐infested soil, soil infested with both the nematode and the fungus, and a noninfested control. Leaf CO2 response curves were measured at early (16 d after inoculation [DAI]) and late (42 DAI) stages of infection for all treatments at saturating light (1500 μmol m−2 s−1 of photosynthetically active radiation [PAR] using a portable photosynthesis system. Carbon dioxide exchange rates were also measured at 1000, 400, and 200 μmol m−2 s−1 PAR to determine leaf light response. At ambient CO2 concentration, concomitant infection by both pathogens significantly reduced C assimilation rate (A) and light use efficiency (μmoles CO2 fixed per μmol of light used), and increased the intercellular CO2 (Ci ) of these young leaves at 42 DAI, but not at 16 DAI. Infection by either pathogen alone had little or no effect on the leaf gas exchange parameters. Analysis of the curve relating A and Ci showed that either treatment alone did not change the initial slope of the curve at 16 DAI. A significant reduction in both the initial slope of A vs. Ci curves and A at Ci = 500 μmol mol−1 in the jointly infected plants were noticeable at 42 DAI indicating that nonstomatal effects could explain the reduction in C assimilation rate at this late stage of disease infection. Leaf patchiness might also be a contributing factor to this phenomena in the leaves of the jointly infected plants.
Cotton Photosynthesis and Carbon Partitioning in Response to Floral Bud Loss Due to Insect Damage
Authors: Holman E.M. , Oosterhuis D.M.
Published: July 2010

To understand better cotton (Gossypium hirsutum L.) plant compensation for early‐season floral bud (square) loss due to insect damage, a field study was conducted in 1994 and 1995 at Marianna, AR. The control treatment was protected by insecticide applications, while tarnished plant bugs (Lygus lineolaris Palisot de Beauvois) and bollworms (Helicoverpa zea Boddie) were released in the plots of the other treatment three times before flowering. Square abscission at the first sympodial fruiting position was 5 and 33% for the control and infested plants, respectively, and yield was reduced 21% by insect infestation. Insect treatment resulted in 4% more light penetration through the canopy, which may have contributed to the 17% increase in photosynthesis of the eighth main‐stem leaf from the terminal leaf as compared with the control plants. Canopy photosynthesis recorded 4 wk after the initiation of flowering was 21% higher in the infested plants. CO2 labeling showed infestation also resulted in more 14C recovered in the terminal node (terminal leaf plus main stem above the terminal leaf) and less remaining in the branch at the same node as the source leaf, which corresponded to an increase in plant height, although node number was not affected. Since our insect‐induced abscission treatments had similar effects as manual fruit removal treatments reported by others, future studies seem justified in using either approach. Early fruit loss in the U.S. Mid‐south results in changes in carbon exchange and allocation, but poor late‐season growing conditions often prevent yield compensation.
Variation in Leaf Starch and Sink Limitations during Seed Filling in Soybean
Authors: Egli D.B.
Published: July 2010

Soybean [Glycine max (L.) Merr.] yield can be limited by the activity of the source (i.e., canopy photosynthesis) or by the ability of the seed (i.e., the sink) to utilize the assimilate produced by the source. An experiment was conducted for 3 yr at Lexington, KY, (38° N latitude) to evaluate potential source‐sink limitations of early and late maturing cultivars. Two early maturing cultivars (Kasota and Hardin, Maturity Group I) and two late maturing cultivars (Essex and Hutcheson, Maturity Group V) were planted in mid‐May in 0.38‐m rows and the plots were irrigated to minimize water stress. Shade cloth that reduced irradiance by 63% was placed over half of the plots from approximately growth stage R6 (early seed filling) to maturity. Shade always significantly reduced the individual seed growth rate (9–32%) indicating that the plants were source limited. Leaf starch levels during seed filling were monitored to evaluate potential sink limitations. Starch levels in the late maturing cultivars usually remained constant or declined during seed filling, providing little evidence of a sink limitation. Starch levels in the early cultivars increased approximately 6‐fold in the early stages of seed filling in 1 of 3 yr, suggesting that, in that year, the plants were sink limited, i.e., the seeds could not use all of the available assimilate. Source limitations during seed filling are apparently common in soybean, but sink limitations seem to occur infrequently in environments where water is not limiting.
Intensity and Duration of Nitrogen Deficiency on Wheat Grain Number
Authors: Jeuffroy Marie‐Hélène , Bouchard Christine
Published: July 2010

In humid temperate climates, N is still a major limiting factor for wheat (Triticum aestivum L.) production. Our objective was to understand and quantify N deficiency effects on the crop grain number to develop optimum N fertilizer management strategies for wheat. In this aim, several experiments were conducted on various soil types and climates with ‘Soissons’ winter wheat. Rates and dates of N fertilizer application were varied in each experiment. This resulted in highly variable dynamics of N accumulation in plants, leading to various N deficiencies throughout the crop cycle. Deficiencies were characterized by a N nutrition index (NNI). Seven criteria describing the deficiency (beginning of deficiency, BD; end of deficiency, ED; duration of deficiency, DD; intensity of deficiency, ID; the product ID × DD = IDD; the lack of nitrogen accumulation at anthesis, LNA; and the NNI at anthesis, NNIa) were estimated for each treatment. Large ranges were obtained for each criterion. Treatments also resulted in highly variable grain numbers. For a N deficient crop, the grain number decrease relative to the control treatment in the same experiment (RGN) was analyzed according to the deficiency criteria. Whatever the grain number component affected (spike number per per square meter or grain number per spike), the RGN appeared to depend on the history of the deficiency, the main explicative variable being IDD, that is, the product of the duration and the intensity of the deficiency. The equation RGN = 1.00355–0.00110 × IDD (R2 = 0.929) allows the prediction of grain number for wheat crops subjected to various N fertilization strategies.
Flurprimidol Effects on Kentucky Bluegrass under Reduced Irradiance
Authors: Stier J. C. , Rogers J. N. , Crum J. R. , Rieke P. E.
Published: July 2010

Turf management in shaded conditions is difficult in part because the reduced irradiance causes excessive shoot elongation, reduced tillering and root growth, and weak plants exceptionally prone to damage. Successful installation of natural grass athletic fields in covered or shaded stadia require improved management procedures. The objective of this study was to determine if flurprimidol [α‐(1‐=‐methylethyl)‐α‐[(trifluourmethoxy)phenyl]‐5‐pyrimidinemethanol], a gibberellic acid (GA)‐biosynthesis inhibitor, could be used to increase turf quality for athletic fields in covered stadia and other reduced irradiance situations. Portable plots of Kentucky bluegrass (Poa pratensis L.) were established outdoors and moved inside a covered‐stadium simulator facility (CSSF). Four rates of flurprimidol (0.56, 1.12, 1.68, and 2.80 kg ha−1) were compared against a control. Studies were conducted under ambient (equivalent to 2–3% full summer sunlight) and supplemental (equivalent to 9–18% full summer sunlight) irradiance. The turf was evaluated with and without simulated soccer traffic. Under ambient irradiance conditions, turf quality generally declined to unacceptable levels within 30 d, although the low rate of flurprimidol extended this period for up to 60 d. Supplemental irradiance provided turf of acceptable quality for up to 70 d and the low rate of flurprimidol extended this period for >100 d. Applications repeated within 30 to 40 d virtually stopped measurable shoot growth under all irradiance and traffic regimes. Flurprimidol did not affect turf shear resistance or rooting but did increase tillering. Low rates of flurprimidol should be useful for maintaining turf in reduced irradiance conditions because turf quality is enhanced with minimal risk of phytotoxicity.
Analysis of the Distribution of the Major Soybean Seed Allergens in a Core Collection of Glycine max Accessions
Authors: Yaklich R.W. , Helm R.M. , Cockrell G. , Herman E.M.
Published: July 2010

P34 is an outlying member of the papain‐superfamily of cysteine proteases that is expressed in developing soybean [Glycine max (L.) Merr.] seeds and may be involved in the defense against Pseudomonas infection. P34 is the major human allergen of soybean seeds and is present in processed food products that contain soybean protein. We have surveyed a core collection of soybean accessions using a monoclonal antibody against P34 and with human sera from soybean‐sensitive individuals. We found that the accessions of soybean surveyed contain similar levels of P34 and that P34 is the major allergenic protein. We have also surveyed wild relatives of soybean and found that P34 was present in the examples assayed. These results indicate that it may not be possible to eliminate P34 from the food supply by breeding with an improved germplasm base.
An Integrated Genetic Linkage Map of the Soybean Genome
Authors: Cregan P.B. , Jarvik T. , Bush A. L. , Shoemaker R. C. , Lark K. G. , Kahler A. L. , Kaya N. , VanToai T. T. , Lohnes D. G. , Chung J. , Specht J. E.
Published: July 2010

A number of molecular genetic maps of the soybean [Glycine max (L.) Merr.] have been developed over the past 10 yr. These maps are primarily based on restriction fragment length polymorphism (RFLP) markers. Parental surveys have shown that most RFLP loci have only two known alleles. However, because the soybean is an ancient polyploid, RFLP probes typically hybridize and map to more than one position in the genome. Thus, the polymorphic potential of an RFLP probe is primarily a function of the frequency of the two alleles at each locus the probe detects. In contrast, simple sequence repeat (SSR) markers are single locus markers with multiple alleles. The polymorphic potential of an SSR marker is dependent on the number of alleles and their frequencies. Single locus markers provide an unambiguous means of defining linkage group homology across mapping populations. The objective of the work reported here was to develop and map a large set of SSR markers. A total of 606 SSR loci were mapped in one or more of three populations: the USDA/Iowa State G. max × G. soja F2 population, the Univ. of Utah Minsoy × Noir 1 recombinant inbred population, and the Univ. of Nebraska Clark × Harosoy F2 population. Each SSR mapped to a single locus in the genome, with a map order that was essentially identical in all three populations. Many SSR loci were segregating in two or all three populations. Thus, it was relatively simple to align the 20+ linkage groups derived from each of the three populations into a consensus set of 20 homologous linkage groups presumed to correspond to the 20 pairs of soybean chromosomes. On the basis of in situ segregation or linkage reports in the literature all but one of the classical linkage groups can now be assigned to a corresponding molecular linkage group.
Occurrence of Fungal Endophytes in Species of Wild Triticum
Authors: Marshall D. , Tunali B. , Nelson L.R.
Published: July 2010

Seedborne, nonpathogenic, fungal endophytes are commonly found in symbiotic relationships with many members of the cool‐season grass subfamily Pooideae The beneficial effects on plants possessing fungal endophytes, and the detrimental effects on consumers of fungal endophyte‐infected plants are widely known. The objective of our research was to determine if fungal endophytes exist in indigenous, wild Triticum (wheat) species from Turkey. From the Triticum species collected, we found two different fungal endophytes. Fungi identified morphologically as members of the genus Neotyphodium were found in the diploid Triticum species T. dichasians (Zhuk.) Bowden and T. tripsacoides (Jaub. & Spach) Bowden. The second endophyte, an Acremonium species, was found in T. columnare (Zhuk.) Morris & Sears, T. cylindricum Ces., T. monococcum L., T. neglecta Morris & Sears, T. recta Morris & Sears, T. triunciale (L.) Raspail, T. turgidum L., and T. umbellulatum (Zhuk.) Bowden. No fungal endophytes were found in T. kotschyi (Boiss.) Bowden, T. ovatum (L.) Raspail, T. peregrinum Morris & Sears, T. speltoides (Tausch) Gren. ex Richter, and T. tauschii (Coss.) Schmal., although the number of samples tested was small for some of these species. Both Acremonium endophyte‐infected and Acremonium endophyte‐free plants of T. triunciale were found to occur at different frequencies at four collection sites on the Anatolian Plateau. Through two selfed generations of the plants, it was found that the Neotyphodium endophyte was transmitted to 100% of the progeny of T. dichasians and T. tripsacoides However, the Acremonium endophytes were not transmitted in all plants that originally possessed them. We concluded that fungal endophytes of the genera Neotyphodium and Acremonium inhabit some wild wheat species grown indigenously in Turkey. These endophytes may influence the ecology and distribution of Triticum species, and may also serve as a source of biological control agents of pests or abiotic stress factors in wheat.
Yield Potential Trends of Tropical Rice since the Release of IR8 and the Challenge of Increasing Rice Yield Potential
Authors: Peng S. , Cassman K. G. , Virmani S. S. , Sheehy J. , Khush G. S.
Published: July 2010

Since the release of IR8 in 1966, 42 additional indica rice (Oryza sativa L.) cultivars developed by the International Rice Research Institute (IRRI) for the irrigated and favorable rainfed lowlands have been released in the Philippines. The maximum yield of IR8 has been reduced by about 2 Mg ha−1 during the past 30 yr. Empirical breeding for population improvement within the indica germplasm has resulted in the maintenance of rice yield potential in the tropics of about 10 Mg ha−1. To break the yield barrier, several approaches are being explored. These include development of a new plant type (NPT) with low tillering capacity and large panicles from tropical japonica germplasm and exploitation of heterosis through intervarietal and intersubspecific hybrids. Hybrid rice between indicas increased yield potential by about 9% under the tropical conditions. The higher yield potential of indica/indica hybrids compared with indica inbred cultivars was attributed to the greater biomass production rather than harvest index. New plant type breeding has not yet improved yield potential due to poor grain filling and low biomass production. Factors that cause poor grain filling and low biomass production of the NPT lines have been identified. Selecting parents with good grain filling traits, introduction of indica genes into NPT's tropical japonica background, and a refinement of the original NPT design are expected to improve the performance of the NPT lines. Further enhancement in yield potential may be possible from use of intersubspecific heterosis between indica and NPT lines.
Synergy of Empirical Breeding, Marker‐Assisted Selection, and Genomics to Increase Crop Yield Potential
Authors: Stuber Charles W. , Polacco Mary , Lynn M.
Published: July 2010

This paper was presented as part of the symposium entitled “Post‐Green Revolution Trends in Crop Yield Potential: Increasing, Stagnant or Greater Resistance to Stress.” In this presentation, we have focused on (i) uses of marker technology in determining the genetic basis of phenotypic expression and the manipulation of phenotypic variation in plants. This included the use of markers in understanding heterosis, in attempts to improve hybrid predictions, in quantitative trait locus (QTL) identification and mapping, in marker‐assisted selection (MAS), and in enhancing breeding success in the development of improved lines and hybrids; (ii) the role of genomics in developing a precise understanding of the genetic basis of phenotypic expression which will then provide more precision in the manipulation of phenotypic variation; and (iii) some attempts to integrate marker technology and genomics into empirical breeding strategies. In addition, we have focused on what has been successful as well as what has fallen short of expectations, and have suggested some of the possible reasons for the lack of success. Because of page limitations, we could not include an exhaustive review of the plant literature and have limited many of our examples to investigations in maize (Zea mays L).
Yield of Wheat in the United Kingdom: Recent Advances and Prospects
Authors: Austin R. B.
Published: July 2010

From 1948 to the present, wheat (Triticum aestivum L.) yields in the UK have increased by an average of 110 kg ha−1 each year. This rate of increase has been at least maintained in recent years. The greater yields have been associated with the adoption of cultivars of shorter stature, which are resistant to lodging and reach anthesis ≈1 wk earlier than old cultivars. In the last two decades, most of these cultivars have carried the rht D1b dwarfing gene. The full yield benefits from modern cultivars have depended on high rates of N fertilization and the use of herbicides and effective fungicides. Data from recent trials with candidate cultivars and F1 hybrids suggest that further genetic gain in yield will be achieved during the next decade. Improved crop protection through chemicals may also enable farmers to obtain greater yields. In the longer term, substantial genetic gain in yield may be achieved if breeders are able to produce cultivars with faster growth rates and greater biomass at maturity. One way to achieve this would be to modify the photosynthetic enzyme rubisco so that its oxygenase activity is reduced. However, cultivars with potentially faster growth rates would require even more N fertilizer if their greater yield potential is to be realized.
Genetics of Soybean Agronomic Traits: II. Interactions between Yield Quantitative Trait Loci in Soybean
Authors: Orf J. H. , Chase K. , Adler F. R. , Mansur L. M. , Lark K. G.
Published: July 2010

In order to breed efficiently, it is necessary to identify individual quantitative trait loci (QTLs) as well as interactions between these loci and to determine which QTLs produce phenotypes that are environment specific. This can be done by linking QTLs to molecular markers. The objective of this research was to carry out such an analysis for yield, one of the most complex agronomic traits. To do this, recombinant inbred lines of soybean [Glycine max (L.) Merrill] were characterized for molecular genetic markers and analyzed for yield in different environments. Interactions between QTLs were identified by subdividing the segregants into four sub‐populations defined by molecular alleles at pairs of unlinked loci. Differences in the mean yields of these sub‐populations defined interactions between QTLs. Measurements of yield in genotyped, recombinant inbred populations derived from crosses of ‘Minsoy’ with ‘Archer’ (MA population) and ‘Noir 1’ with Archer (NA population) have identified a pair of interacting yield QTLs whose effect was independent of environment as well as a pair of loci whose interaction was environment specific. Each example of epistasis, involved an allele specific interaction between the two QTLs. In the NA population, a pair of QTLs was identified in which Noir 1 alleles interact to specify a significant increase in yield that is not environment specific. These loci, located on linkage groups (LG) U3 and U9, do not affect either height or maturity. In all environments, the interaction between the QTLs was significant. In the MA population, a pair of QTLs was identified in which the Minsoy alleles interact to specify a significant increase in yield. However, this significant interaction is environment specific. One of the loci (on LG U14) is also associated with effects on height, seed weight, and maturity that are found in other environments, but these latter effects do not appear to involve any interactions with other loci. The data from the MA population support the concept that interactions between QTLs also can result in location‐specific effects on quantitative traits.
Transfer of Wheat‐Rye Translocation Chromosomes Conferring Resistance to Hessian Fly from Bread Wheat into Durum Wheat
Authors: Friebe B. , Kynast R. G. , Hatchett J. H. , Sears R. G. , Wilson D. L. , Gill B. S.
Published: July 2010

The Hessian fly, Mayetiola destructor (Say), is a damaging pest of bread wheat, Triticum aestivum L., and durum wheat, T. turgidum L. ssp. durum Desf. Husn., in many wheat production areas of the world. Breeding for host plant resistance is the most agronomically desirable way to control this pest. Twenty‐seven major genes conferring resistance to Hessian fly have been identified and used in wheat improvement. These genes confer resistance to specific biotypes of the Hessian fly. Recently, new sources of Hessian fly resistance derived from cultivated rye, Secale cereale L., have been reported that confer resistance to all known biotypes of the Hessian fly. The resistance gene H21 is present on the wheat‐rye whole arm translocation T2BS·2R#2L. H25 is present on an interstitial rye segment in the 4AL arm of the wheat‐rye translocation chromosome Ti4AS·4AL‐6R#1L‐4AL. The objective of the present study was to transfer H21 and H25 to tetraploid durum wheat, thereby making these genes available for the improvement of durum wheat. Homozygous T2BS·2R#2L and Ti4AS·4AL‐6R#1L‐4AL translocation durum lines were recovered that expressed the H21 and H25 resistance. The H25 durum translocation line was vigorous and set seeds similar to the durum wheat parental cultivar. Thus, the H25 transfer can be used directly in durum wheat improvement. Plant vigor and seed set of the H21 durum translocation line was drastically reduced, indicating that the missing 2BL arm in this translocation has genes that are essential for normal plant vigor and fertility. Further chromosome engineering is required to shorten the rye segment in this translocation before H21 can be used in durum breeding.
Molecular Mapping of Russian Wheat Aphid Resistance from Triticale Accession PI 386156
Authors: Fritz A. K. , Caldwell S. , Worrall W. D.
Published: July 2010

The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is an economic pest of wheat (Triticum aestivum L.) in some western growing regions. Sources of resistance occur within the wheat gene pool, but there are also high levels of resistance in wheat relatives, including rye (Secale cereale L.). An F2 population between PI 386156, a Russian wheat aphid‐resistant triticale (×Triticosecale Wittmack) from Russia and NE88T222, a susceptible triticale, was used to examine the inheritance of resistance. Five distinct classes of reaction to the RWA were observed, suggesting this trait is not controlled by a single dominant gene in this population. Bulked segregant analysis was performed with DNA from plants representing the most resistant (‘R’) and most susceptible (‘S’) classes. A co‐dominant marker amplified by primer OP‐M09 explained more than 55% of the variation observed for resistance. Sequencing results revealed a deletion in the ‘S’ parent relative to the ‘R’ parent. Using a set of wheat‐rye addition lines, we mapped the target fragment to chromosome 4R, which has previously been identified as the critical chromosome for RWA resistance from PI 386156 and other Russian triticales.
Mapping and Genetic Analysis of the Genes for Photoperiod‐Sensitive Genic Male Sterility in Rice Using the Original Mutant Nongken 58S
Authors: Mei M. H. , Dai X. K. , Xu C. G. , Zhang Qifa
Published: July 2010

Photoperiod‐sensitive genic male sterility (PSGMS) rice has a number of desirable characteristics for hybrid rice production. In this study, we conducted a molecular marker‐based mapping and genetic analysis of PSGMS genes using two crosses involving the original mutant Nongken 58S as the PSGMS parent. The genomic locations of the PSGMS loci were determined following the “bulked extreme and recessive class” approach, in which the regions containing the PSGMS loci were identified by assaying the bulks of extreme phenotypes and the distances between the PSGMS loci and molecular markers were calculated from the highly sterile plants of the F2 populations. Two PSGMS loci, located on chromosomes 7 and 12, respectively, were identified in both crosses. The locus on chromosome 7 was the same as pms1, identified previously in a cross between an indica PSGMS line and an indica cultivar. The one on chromosome 12 was a new locus that we designated as pms3 Both loci had major effects on fertility and acted like a pair of classical duplicated genes in controlling male sterility. Comparison of the present finding with previous results indicated a complex genetic basis of PSGMS. The implications of such genetic complexity in breeding for PSGMS lines are also discussed.
Molecular Mapping of Loci for Agronomic Traits on Chromosome 3A of Bread Wheat
Authors: Shah M. M. , Gill K. S. , Baenziger P. S. , Yen Y. , Kaeppler S. M. , Ariyarathne H. M.
Published: July 2010

Chromosome 3A of bread wheat (Triticum aestivum L.) cultivar ‘Wichita’ (WI) was previously found to differ from that of ‘Cheyenne’ (CNN) for genes affecting a number of agronomically important traits such as grain yield (GYLD), kernel number spike−1 (KPS), 1000‐kernel weight (TKWT), spike number m−2 (SPSM), grain volume weight (GVWT), plant height (PHT), and anthesis date (influenced by Eps locus). This study was designed to map the Eps locus and to identify regions of chromosome 3A of wheat associated with agronomic traits. A population of 3A recombinant inbred chromosome lines (RICLs‐3A) was previously evaluated in replicated field trials. Thirteen RFLPs and one morphological marker locus, Eps, were used to develop a genetic linkage map and to identify QTLs associated with agronomic traits. Individual loci explained from 8.9 to 38.2% of the total phenotypic variation for the measured traits. The major locus Eps was mapped distal to an RFLP marker locus Xcdo549 on the short arm of chromosome 3A and explained 38.2% of the total phenotypic variation for PHT, and 17.4% for both KPS and TKWT. Additional QTLs for PHT, TKWT, and KPS were identified on the chromosome. A QTL for SPSM on the long arm of chromosome 3A was tightly linked to QTL for PHT and KPS. QTLs for GYLD were identified only in a few individual environments whereas no QTL was detected for GVWT. No epistasis was detected between markers associated with QTLs. The QTLs identified across environments were consistent in all or most environments, hence should be useful in future marker assisted selection programs for breeding wheat cultivars.
Relationship between Photosynthesis and Seed Number at Phloem Isolated Nodes in Soybean
Authors: Bruening W. P. , Egli D. B.
Published: July 2010

Seed number is the primary yield component in soybean [Glycine max (L.) Merrill], but the mechanisms responsible for the regulation of this component are not fully understood. Three soybean cultivars (Elgin 87, Emerald, and Essex) with genetic differences in seed growth rate and seed size were grown in the field in 1995 and 1996 to determine the relationship between photosynthesis, sink characteristics, and seed number at individual nodes. The sixth node from the bottom of the main stem was isolated by heat girdling the stem below the node to disrupt phloem continuity and by removing the part of the plant above the girdled node when flowers first opened at this node. Photosynthesis was varied by defoliating (removing approximately 0, 33, 66, 83, or 100% of the leaf area) the leaf at the girdled node. Carbon dioxide exchange rate (CER) was measured at approximately weekly intervals for up to 40 d after girdling. Girdling temporarily reduced CER in four of six comparisons and defoliation tended to increase CER. Defoliation produced large differences in nodal carbon input (NCI) per node and seed number increased rapidly as average NCI per node increased from 0 to approximately 0.10 μmol CO2 node−1 s−2 However, there was no further increase in seed number as average NCI continued to increase to 0.5 μmol CO2 node−1 s−2, suggesting that isolated nodes respond differently than soybean communities. Maximum seed number per node was inversely related to cultivar differences in individual seed growth rate and seed size. The girdled node technique should prove useful to investigate seed number‐photosynthesis relationships in soybean.
Carbon Isotope Discrimination as a Tool to Improve Water‐Use Efficiency in Tomato
Authors: Martin Bjorn , Tauer Charles G. , Lin Robert K.
Published: July 2010

Carbon isotope discrimination (Δ) is a property that may be used to improve water‐use efficiency (WUE). This study tested the association between Δ and WUE with plant materials and growth conditions likely to disrupt the link between Δ and WUE. The cultivated tomato, Lycopersicon esculentum Mill. cv. UC82B, a drought‐resistant related species, L. pennellii (Cor.) D'Arcy accession LA716, and the F1 and F2 generations of the L. esculentum × L. pennellii cross were grown in containers in wet and dry field environments. The wet environment was repeated in a second year and plants were split into groups terminated early and late in the season. The F1 generation had greater mean WUE and dry weight (DW) than L. esculentum, but the DW advantage was not maintained in the F2 generation. Low Δ of L. pennellii suggested that leaf WUE was high, but its whole plant WUE varied relative to the other plant materials in the different environments. There was a negative correlation between Δ and WUE in the F2 generation, and WUE was generally positively correlated with DW. However, low Δ was associated with large DW in only one environment and with small DW in three environments. Averaged across environments, the top 10% of the plants ranked by WUE had 47% greater WUE than the bottom 10%. In comparison, the bottom 10% ranked by Δ had an average of 16% greater WUE than the top Δ group, but in three of the four environments the bottom group accumulated 33 to 47% less DW than the top Δ group. This study on tomato suggests that WUE can be increased by selecting low Δ, but selecting low Δ alone may identify a subpopulation of small plants. Dry weight could probably be increased by traditional breeding techniques.
Response of Cassava to Water Deficit: Leaf Area Growth and Abscisic Acid
Authors: Alves Alfredo A. C. , Setter Tim L.
Published: July 2010

Cassava (Manihot esculenta Crantz) responds to decreases in water status by pronounced stomatal closure and decreased leaf area growth. Many water deficit responses are thought to be regulated by abscisic acid (ABA). To evaluate the extent to which ABA accumulated in a temporal pattern related to water deficit and leaf area growth, five cassava genotypes were grown in greenhouse conditions and subjected to water deficit and recovery treatments during the vegetative‐growth stage. Young and mature leaves were sampled for analysis of area growth and ABA. Under water deficit, leaves from all genotypes rapidly accumulated large amounts of ABA in both mature and young leaves. Correspondingly, young leaves halted leaf expansion growth and transpiration rate decreased. Young leaves accumulated more ABA than mature leaves in both the control and stressed treatments. The high ABA levels under water deficit were completely reversed to control levels after 1 d of rewatering. This rapid return to control ABA levels corresponded with a rapid recovery of leaf area growth rates. We postulate that the rapid reduction in leaf area growth and stomatal closure observed in our study may be due to cassava's ability to rapidly synthesize and accumulate ABA at an early phase of a water deficit episode.
A Twelve‐Hour In Vitro Procedure for Sorghum Grain Feed Quality Assessment
Authors: Pedersen J. F. , Milton Todd , Mass R. A.
Published: July 2010

Improved methods for assessing cereal crop feed value are a prerequisite for the genetic improvement of sorghum [Sorghum bicolor (L.) Moench] feed value. Rate of starch digestion is now commonly believed to be the limiting factor in sorghum utilization by cattle (Bos taurus). However, techniques to assess this trait are not useful to sorghum breeders because of high labor inputs, lab error associated with starch measurement, and need for high numbers of replications. The objective of this study was to develop a simple technique capable of identifying differences in digestion between sorghum and corn (Zea mays L.) and detecting differences among sorghum genotypes. In vitro starch and dry matter digestion were measured on sorghum and corn lab standards at 0, 6, 12, 18, 24, 30, and 40 h. Maximum differentiation between corn and sorghum dry matter digestion (345 vs. 253 g kg−1) and starch digestion (403 vs. 301 g kg−1) occurred at 12 h, and dry matter and starch digestion were highly correlated (r = 0.99). Differences among five sorghum lines were significant for 12‐h dry matter digestion and ranged from 229 to 272 g kg−1. This procedure provides a precise and rapid technique that can be used by feed grain breeders to evaluate modifications in grain digestion parameters.
Efficiency of the Use of Doubled‐Haploids in Recurrent Selection for Combining Ability
Authors: Bouchez A. , Gallais A.
Published: July 2010

In population improvement for combining ability, the use of selfed progenies increases genetic advance per cycle, but it can unduly increase the cycle length. Haplodiploidization (HD) can be very efficient because it induces complete homozygosity in a short period. We compared, from a theoretical approach, the potential of recurrent selection with a tester using doubled haploids (SDHT), with selection with testcrosses of S0, S1, or S2 plants, with or without the use of off‐season nurseries, for an annual plant like maize (Zea mays L.). With the same selection intensity, and without off‐season nurseries, SDHT with a 4‐yr cycle is the most efficient method. Efficiency increases with lower heritability, with an advantage in comparison to the test of S0 plants (S0T) of 40 to 50% at low heritability (h2 < 0.15) and 12% at high heritability (h2 = 0.8). Use of off‐season nurseries reduces the advantage of SDHT. With a 3‐yr cycle, SDHT remains the best at low heritability with a gain of 27% (for h2 = 0.1) in comparison to S0T with a 2‐yr cycle. When using constant effective size, the advantage of SDHT is further reduced or suppressed at the benefit of S0T in 2 yr. The use of HD in recurrent selection for combining ability has its biggest advantage when heritability is low. Consideration of variety development will give more advantage to HD.
Patterns of Variation in a Collection of Meadow Fescue Accessions
Authors: Casler Michael D. , van Santen Edzard
Published: July 2010

Meadow fescue (Festuca pratensis Huds.) is a pasture grass that has been little used in North America since the introduction of its higher yielding relative tall fescue (F. arundinacea Schreb.). The objectives of this study were to quantify genotypic variation for agronomic traits within the USDA National Plant Germplasm System (NPGS) collection of meadow fescue accessions and to relate that variation to the geographic source of the accessions. Seedlings of 213 accessions were transplanted to Ashland and Marshfield, WI, and to Crossville, AL, in 1991. Four spaced plants per accession, overseeded with white clover (Trifolium repens L.), were established at each location. Forage yield, disease reaction, morphological traits, maturity, and survival were determined in 1992 and 1993. For most traits, accessions responded similarly at the two Wisconsin locations, but differently between Wisconsin and Alabama. Phenotypic correlations between the two states were positive, but very low. Between 18 and 36% of the sum of squares for accessions was due to country or region source of each accession. Romanian and Hungarian accessions had the highest mean forage yield, with superior survival in both Wisconsin and Alabama. Several accessions had short, narrow leaf blades, thin stems, wide crowns, and high survival, suggesting potential use as turf‐type germplasm. A core collection of 55 accessions was proposed on the basis of cluster analysis classification.