bluuebunny/crossref_metadata_2025 huggingface dataset:
Monogenic Dominant Sulfonylurea Resistance in Sugarbeet from Somatic Cell Selection
Authors: Saunders Joseph W. , Acquaah George , Renner Karen A. , Doley William P.
Published: July 2010

Injury to sugarbeet, Beta vulgaris L., from sulfonylurea herbicide residues from preceding cropping years has kindled interest in developing resistant cultivars. This study was conducted to obtain chlorsulfuron (2‐chloro‐N‐[[(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)amino]carbonyl]benzenesulfonamide) resistance from cell cultures and to determine its inheritance and magnitude. Utilizing annual diploid sugarbeet clone REL‐1, dispersed suspension cultures were initiated from callus induced on leaf disk cultured on a modified Murashige and Skoog (MS) agar medium + 1.0 mg L−1 N6‐benzyladenine (BA) and placed in the liquid form of the same medium. Unmutagenized cell clusters were plated on solid medium containing 2.8 nM chlorsulfuron in MS + 1.0 mg L−1 BA. A single colony arose, from which shoots were regenerated. Shoots were resistant to 28 nM chlorsulfuron, a concentration that killed similar shoots of REL‐1. Resistance (designated Sur) was inherited as a monogenic dominant. In vitro shoot resistance to chlorsulfuron was 300 to 1000‐fold greater than in REL‐1. Resistance was also expressed in leaf disk expansion in vitro with MS + 1.0 mg L−1 BA.
Acremonium Endophyte Effects on Tall Fescue Drought Tolerance
Authors: White Richard H. , Engelke Milton C. , Morton Sharon J. , Johnson‐Cicalese Jennifer M. , Ruemmele Bridget A.
Published: July 2010

Tall fescue (Festuca arundinacea Schreb.) is grown as a forage, turfgrass, and conservation grass from the Gulf Coast to Canada in the eastern USA. The presence of endophytes in grasses can confer resistance to insect pests, enhance growth, and improve tall fescue persistence under high temperature and drought stress. Most tall fescue is infected with Acremonium coenophialum Morgan‐Jones & Gams, a fungal endophyte. Our objectives were to determine the effects of endophyte infection on water relations and survival of water stressed (i.e., drought‐stressed) tall rescue under greenhouse conditions. Endophyte‐free and infected plants of three tall fescue selections were vegetatively propagated and grown together in 38‐L weighing lysimeters to allow interplant competition for available soil moisture. Irrigation water and fertilizer were applied for 12 wk after planting before irrigation water was withheld for 8 wk. Water‐relation characteristics including full‐turgor osmotic potential (ψπ100), water potential at zero turgot (ψL0), relative water content at zero turgot (RWC0), apoplastic water fraction (β), bulk modulus tissue elasticity (ϵ), and the turgid weight to dry weight ratio (TW/DW) were determined before and after water stress. Osmotic adjustment (Δψπ) was also determined. Endophytein fection did not affect ψπ100, ψL0, RWC0, and β either before or after water stress and did not affect Δψπ. Endophyte infection did affect ϵ and the TW/DW ratio, but this effect was not sufficient to alter ψL0. Total tillers, tiller survival, plant survival, and recovery weights were similar for endophyte‐free and ‐infected plants. No evidence for endophyte‐mediated drought tolerance was observed in this study. Based on this work, endophyte‐mediated drought resistance may be due to alterations in drought avoidance.
Combining Vigor Test Results for Prediction of Final Stand of Shrunken‐2 Sweet Corn Seed
Authors: Wilson Dale O. , Alleyne John C. , Shafii Bahman , Mohan S. Krishna
Published: July 2010

Supersweet sweet corn (Zea mays L.) based on the shrunken‐2 gene suffers from low and erratic field emergence and seedling survival. The purpose of this project was to find seed vigor tests highly correlated with final stand count, and to combine tests to form a multiple regression model for prediction of final stand. Forty‐nine commercial seed lots (and one noncommercial lot) obtained in 1988 and 48 lots obtained in 1989 were planted in the field the next year. Final stand (FS) was counted at the six‐leaf stage. The standard rolled‐towel germination test with counts at 4 (G4) and 7 d (G7) was performed, along with accelerated aging (AA), soil cold test (CT), fat acidity of kernels (FA), kernel weight (WT), embryo weight (EM), ratio of EM to WT, and leachate conductivity (EC). The G7 and G4 counts were not highly correlated with FS (r < 0.40). The test most highly correlated with FS in the 1988 seed was EC (r = −0.62); in the 1989 seed, it was AA (r = 0.87). The EC and AA tests were complementary, and were combined using linear multiple regression into vigor indices. In 1988, the optimum model involved the variables AA, EC, and EM (R2 = 0.69); in 1989, only AA and EC (R2 = 0.78). Models were cross‐validated by using the regression equation from one year to predict field emergence in the other year. When the 1988 multiple regression model was cross‐validated using 1989 data, it was highly correlated with FS (r = 0.86); the 1989 equation cross‐validated using the 1988 data was likewise highly correlated with FS (r = 0.64). Collinearity was detected among the explanatory variables, but was not strong enough to influence the regression results. Since AA and EC proved to be complementary tests, multiple regression was a useful way to combine them and other test results for prediction of final stand.
Relationships between the fan Allele and Agronomic Traits in Soybean
Authors: Wilcox James R. , Nickell Andew D. , Cavins James F.
Published: July 2010

Normal levels of linolenic acid (70‐80 g kg‐1) in soybean [Glycine max (L.) Merr.] oil adversely affect oil flavor and stability. The mutation‐induced line C1640 has half the normal level of linolenic acid (37 g kg‐1), but is 24% lower yielding than ‘Century’, from which it was selected. This study was conducted to determine if there are genetic relationships betweena gronomictr aits and the fan allele for low linolenic acid identified in C1640. Century and ‘Harper’, both with the FanFan alleles for normal 18:3, were crossed with C1640 containing the fanfan alleles for low 18:3. Both FanFan and fanfan segregates from the two crosses were evaluated for agronomic traits and linolenic acid in replicated tests over a 2‐yr period on a Chalmers soil (fine‐silty, mixed, mesic Typic Haplaquoll) at the Purdue University Agronomy Research Center near West Lafayette, IN. The fanfan segregates in the Century × C1640 cross averaged slightly higher in seed yield and taller in plant height than the FanFans egregates. In the Harper × C1640 cross, fanfan segregates averaged 1 d later in maturity than FanFan segregates. Mean values for FanFan and fanfan segregates for other traits in both crosses were essentially the same. These data indicate that there are no associations between the fanfan alleles and those agronomic traits needed in commercial soybean cultivars with low levels of linolenic acid. Apparently the low yield of C1640 is controlled by genetic changes independent of the mutation for low 18:3. Regression of linolenic acid level on maturity dates for both FanFan and fanfan segregates in the Harper × C1640 cross show that segregates of both genotypes tended to have increased linolenic acid at later maturity dates. This could be attributed to the cooler temperatures during seed maturation to which the later maturing segregates were exposed.
Photosynthesis and Stomatal Conductance of Symbiotic and Nonsymbiotic Tall Fescue
Authors: Richardson Michael D. , Hoveland Carl S. , Bacon Charles W.
Published: July 2010

Desirable and undesirable agronomic characteristics of tall fescue (Festuca arundinacea Schceb.) have been attributed to infection by a nonpathogenic fungai endophyte (Acremonium coenophialum Morgan‐ Jones & Gams, section Alba.lanosa). It has been suggested that stomatal control of water loss is more closely regulated in symbiotic than nonsymbiotic tall fescue, a feature that may improve drought resistance. A greenhouse experiment was designed to study apparent photosynthesis, stomatal conductance, transpiration, and leaf water potential in two genotypes of symbiotic and nonsymbiotic tall fescue grown in polyethylene glycol solutions of ‐0.1, ‐0.3, ‐0.7, and ‐1.0 MPa water potential. Symbiotic plants of one genotype (CB1) had slightly higher photosynthesis, stomatal conductance, and transpiration at intermediate levels of water stress than nonsymbiotic plants. Gas exchange of the second genotype (DNT) may have been affected by endophyte infection, as photosynthetic rates of symbiotic plants grown at ‐1.0 MPa were slightly higher than nonsymbiotic plants. The increased photosynthesis and stomatal conductance in genotype CB1 were apparently the result of turgor maintenance in mature leaves of symbiotic plants. At moderate and low water potential, leaves of symbiotic plants had a greater turgor potential than nonsymbiotic plants. These data suggest that the endophyte of genotype CB1 does not enhance stomatal closure under water deficit stress, but induces a more favorable turgor pressure in mature leaves, which may lead to greater photosynthesis at lower water potentials.
Gas Exchange, Carbon Isotope Discrimination, and Productivity in Winter Wheat
Authors: Morgan Jack A. , LeCain Daniel R. , McCaig Thomas N. , Quick James S.
Published: July 2010

Leaf gas exchange theory indicates that carbon isotope discrimination (∆) is negatively associated with CER/g3 (leaf CO2 exchange rate/conductance). Discovery of genetic variation for ∆ in wheat (Triticum aestivum L.) and other species has generated interest in using carbon isotope discrimination in plant breeding. However, the hypothesized negative association between CER/g3 and & has sometimes not been observed in field‐grown crops. In the present study, CER/g3, & of peduncle tissue, plant productivity and yield were examined in eight winter wheat genotypes under both irrigated and nonirrigated field conditions. Water stress‐ and genotype‐induced variations in CER/g3 were more consistently correlated with variations in gs than with CER. However, low CER in ‘Bezostaya’ wheat resulted in a consistently low genotypic ranking for CER/g3. In 1988, values of CER/g3 increased with water stress, while ∆ values dropped from 18.17 to 17.48‰. These results imply a negative relationship between CER/g3 and ∆, consistent with leaf gas exchange theory; however, ∆ was both positively (1988; r = 0.83** [P ≤ 0.01]) and negatively (1989; r = ‐0.79* [P ≤ 0.05]) associated with CER/g3 in irrigated plots. Positive correlations were obtained between ∆ and both biomass productivity (1988, r = 0.54*; 1989, r = 0.45 [P = 0.08]) and grain yield (1988, r = 0.66*; 1989, r = 0.55*) when data were averaged across genotypes and irrigation treatments. Consistently low ∆ values were obtained for ‘Sturdy’, an early‐released, drought‐susceptible cultivar with low productivity. These results suggest that genotypic rankings for peduncle ∆ must be carefully interpreted, as low ∆ can be associated with low yield and stress susceptibility in wheat.
Use of Tassel‐Seed (Ts‐5) Maize for Assimilate Transport Studies Using Intact or Detached Tassel Branches
Authors: Thomas Paul A. , Felker Frederick C. , Shannon Jack C. , Crawford C. Gerald
Published: July 2010

The anatomy of normal maize (Zea mays L.) ears precludes easy access to the kernel pedicel tissue for in vivo assimilate transport experiments. We investigated the possibility of using the Tassel‐seed (Ts‐5) mutant of maize as a model system for studies of assimilate movement into developing maize kernels. Hypodermic needles (26 gauge, 9.5 mm long) inserted under the pedicel epidermis of intact plants were used to introduce solutes into the pedicel free space. Additionally, excised tassel branches were incubated in buffered solutions containing 100 mM 14C.labeled sugars. The movement of apoplastic and symplastic fluorescent dyes as well as 14C‐iabeled assimilates and incubation solutions showed that Ts‐5 maize provides a useful experimental system for study of the mechanism of assimilate transport into developing kernels.
Batch Anion Exchange Separation and Quantification Of [14C]Hexose from [14C]Sucrose
Authors: Tarpley Lee , Dahlberg Jeffrey A. , Vietor Donald M. , Miller Frederick R.
Published: July 2010

Techniques quantifying 14C]photoassimilate partitioning between hexose and sucrose can identify developmental and regulatory changes in sugar metabolism of sorghum [Sorghum bicolor (L.) Moench]. The objective of this study was to develop a laboratory method for separating and quantifying [14C]hexose and [14C]sucrose in numerous plant organ extracts simultaneously. The described method combines easily with available assays for [14C]starch and [14C]structural components and for total fructose, glucose, sucrose, and starch. Treatment with hexokinase is followed by batch treatment with anion exchange resin. Hexose, as hexose phosphate, binds (>95%) to the resin, and sucrose remains unbound (>95%). Radiolabel in extracts is nearly completely recovered (99%). Determinations are reproducible (SE = 1.3%). This method was applied to identify differences in sugar metabolism between organs and among growth stages of field‐grown sorghum.
RFLP Analysis of Genomic Regions Associated with Resistance to Preharvest Sprouting in Wheat
Authors: Anderson James A. , Sorrells Mark E. , Tanksley Steven D.
Published: July 2010

Resistance to preharvest sprouting (PHS) is difficult to incorporate into new varieties because heritability is low and selection is limited to one generation per year. Our objective was to identify genomic regions containing quantitative trait loci (QTL) associated with resistance to PHS in two recombinant inbred (R) populations of white wheat (Triticum aestivum L. em. Thell.) by restriction fragment length polymorphism (RFLP) markers. One population consisted of 78 RI lines from the cross of NY6432‐18 (NY18) × ‘Clark's Cream’ (CC). The second population consisted of 138 RI lines from the cross between sib lines NY18 and NY6432‐10 (NY10). The NY18/CC and NY18/10 populations were evaluated for PHS in six and seven environments, respectively, by examining physiologically mature spikes under simulated rainfall. The three parental lines were surveyed for polymorphism with 195 low‐copy RFLP clones. Individual RI lines from the NY18/CC and NY18/NY10 populations were probed with 37 and 27 polymorphic clones, respectively. Eight regions of the genome (four from each population) were significantly associated with resistance to PHS. Based on multiple regression, specific sets of markers and their interactions accounted for 44% of the genetic variance for PHS in the NY18/CC and 51% in the NY18/NY10 populations. These markers could find utility in breeding programs as indirect selection criteria for improvement of PHS resistance.
Accumulation of Fructan Trisaccharides in Leaves of Four Winter Cereals
Authors: Slaughter Leon H. , Sammons David J.
Published: July 2010

Winter cereals produce substantial quantities of fructan (β‐D‐fructofuranosyl polymer terminating in sucrose) and relatively little starch in stems and leaves. Although fructan is produced by economically important crops, little is known about fructan degree of polymerization (DP), distribution, synthesis, and degradation. Field studies in Maryland during winter and spring were used to examine changes in the pattern of accumulation of three fructan trisaccharides, 1‐kestose, 6‐kestose, and neokestose in oat (Avena sativa L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and rye (Secale cereale L.). Oat contained the greatest amount of total trisaccharide followed by rye, wheat, and barley. The 1‐kestose was the predominant trisaccharide in wheat, rye, and barley leaves. Wheat and rye contained significantly higher levels of 1‐kestose than oat on most sample dates. Oat leaves contained significantly greater amounts of 6‐kestose and neokestose than the other cereals. In April, 6‐kestose accounted for 64% of the total trisaccharide in oat leaves. On most sample dates wheat and barley leaves contained no neokestose. Nystose, a DP 4 fructan, was present in leaf tissue at each sampling; however, the concentration was below 1 mg g−1 dry weight in all species examined. Rye contained significantly greater amounts of nystose than wheat, barley, and oat when averaged across sample dates. Variation in trisaccharides and nystose suggest that different enzymes may exist in oat compared to the other cereal species.
Characterization of Meadowfoam CO2 Exchange Rates
Authors: Seddigh Majid , Jolliff Gary D. , Breen Patrick J.
Published: July 2010

Recent evidence suggests that meadowfoam (Limnanthes alba Hartweg ex Benth.) seed‐set and seed‐fill may be limited by the availability of photoassimilates. Our objectives were to determine the CO2 exchange rates (CER) of leaves (rosette and stem leaves), stems, and sepals of “Mermaid” meadowfoam in controlled environments, and to evaluate the variability in leaf net photosynthesis within and between field.grown selections. We used a semi‐closed compensating system to measure the CER of different parts of potted plants in a controlled environment. We also measured net photosynthesis for single leaves of solid‐stand or single‐spaced plants of field‐grown meadowfoam selections using a portable photosynthesis system. Net photosynthesis and respiration rates of Mermaid rosette leaves at vegetative stage averaged 19.2 and 4.0/μmol m−2 s−1, respectively. These values were similar to those for rosette leaves during early stem growth and the leaves on flowering stems. Net photosynthesis of rosette leaves during early flowering averaged only 7.9 μmol m−2 s−1. The CER of sepals was similar to that of leaves on flowering stems. Because most leaves senesce by mid flowering, the contribution of sepal photosynthesis to seed fill could be significant. The stem net photosynthesis during flowering on a per plant basis was only 7% of that for the sepals. Differences among field‐grown selections for phytomass and seed production were not associated with their variations in net photosynthesis of single leaves measured instantaneously. Photosynthetic capacity of sepals and stems, however, may play a role in determining potential seed yield of meadowfoam.
Evidence of Geographical Divergence in Kabuli Chickpea from Germplasm Evaluation Data
Authors: Jana Sakti , Singh Khadag B.
Published: July 2010

Turkey is the putative center of origin of cultivated chickpea, Cicer arietinum L. The large‐seeded kabuli chickpea is the most common type cultivated in West Asia and the Mediterranean region. This type is believed to have diverged from its ancestral small‐seeded, desi type in the Mediterranean region, and spread to India in the east and Chile in the west. Differences in agro‐climatic conditions and farmers' preferences for the species may have produced geographical differentiation of interest both in agriculture and crop evolution. The objective of this study was to test whether geographical divergence in kabuli chickpea is consistent with the proposed theory of its spread from its putative center of origin. More than 4000 kabuli chickpea accessions representing Turkey and six other major chickpea‐growing regions were grown in a winter‐sown nursery at the International Center for Agricultural Research in the Dry Areas (ICARDA), near Aeppo, Syria, and characterized for nine morphological, three phenological and four physiological characters. Accessions in each region were grouped in three broadly defined classes: desirable, undesirable, and intermediate. These classes were determined on the basis of human preference and plant breeding experiences in the semi‐arid Mediterranean region. Frequencies in respective classes were recorded for each character. Frequency distributions were significantly different among the regions. The highest frequency of accessions in the desirable class for eight of the 16 characters was found in the regions west of Turkey, and for four characters in the regions east of Turkey. Five traits; growth habit, canopy width, plant height, seed size, and days to maturity were used to examine multicharacter associations in different regions. The discrete log‐linear multivariate analysis showed two‐character associations, but no higher order associations in any region. The most frequently occurring association was between plant height and canopy width. Multivariate principal components analysis of 11 quantitative traits revealed that the distribution of chickpea on both sides of Turkey was consistent with the proposed pathway.
Resistance to Leaf Rust in 26 Mexican Wheat Cultivars
Authors: Singh Ravi P.
Published: July 2010

CIMMYT germplasm derived wheat (Triticum aestivum L.) cultivars are grown on a large area worldwide. The status of leaf rust Puccinia recondita Roberge ex Desmaz. f. sp. tritici resistance in various cultivars is unknown. In this study, designated Lr genes were postulated in 26 cultivars released in Mexico between 1950 and 1989 by inoculating their seedlings with 14 pathotypes of diverse avirulence—virulence combinations. The adult plant resistance was evaluated with two currently predominant pathotypes during 1991–1992 crop cycle at Ciudad Obregon in northwest Mexico. Additionally, the probable presence of Lr13 and Lr34 was identified by determining the presence of linked genes Ne2 and Ltn, respectively. Eight Lr genes were present either singly or in combination: Lr1 (in 12 cultivars), Lr3 (4), Lr13 (18), Lr16 (1), Lr17 (3), Lr23 (2), Lr26 (1), and Lr34 (13). Virulence existed for the above genes, except Lr34. The 13 cultivars with Lr34 displayed low to intermediate adult plant disease severities and reduced area under the disease progress curve (AUDPC). Variation in the adult plant disease responses of these cultivars indicated the presence of additional genes for resistances. Lr34 has provided durable leaf rust resistance since the release of Yaqui 50. Several other cultivars lacking Lr34 also displayed reduced ADUPC. A complete database on leaf rust resistance genes in Mexican wheat cultivars has use in increasing genetic diversity in cultivars currently grown. Furthermore, based on the present information additional useful genes can be incorporated in the new germplasm.
Selection for Grain Yield following Selection for Ear Height in Maize
Authors: Burgess Janet C. , West D. R.
Published: July 2010

Recurrent selection improves population performance by increasing the frequency of favorable alleles. In maize (Zea mays L.), the higher frequency of favorable alleles in a population is expected to result in improved performance of inbred lines and hybrids derived from the population. This study was conducted to evaluate the responses to four cycles of selection for grain yield, after 10 cycles of selection for ear height. During selection for reduced ear height, grain yield had declined 29%. Tennessee Late Low‐Ear synthetic cycle 10 was used to initiate S1 and testcross (TC) selection for grain yield. Individual plants were selfed and crossed to a single cross for TC selection, or selfed only for S1 selection. Ten progenies were selected from 100 evaluated in yield trials, and remnant S1 seed were intermated to complete each cycle of selection. Response to selection for grain yield was evaluated for each cycle of selection as random‐mated, bulk inbred, and hybrid populations at two locations for 2 yr. The response to S1 selection was a 44% yield increase after four cycles, and TC selection resulted in a 21% yield gain in random‐mated populations. Hybrid and inbred yields were also increased by selection, but the gains were less than for random‐mated populations. Ear height increased 8% in Cycle 1 of selection for yield, but did not change in later cycles. Four cycles of recurrent family selection restored grain yield to approximately the level of the population before selection for low‐ear placement.
Improved Semidwarf Rice Lines with Tolerance to Submergence of Seedlings
Authors: Mackill D. J. , Amante M. M. , Vergara B. S. , Sarkarung S.
Published: July 2010

Short‐term submergence of rainfed lowland and deepwater rice (Oryza sativa L.) reduces yields on millions of hectares in South and Southeast Asia. Farmers in these areas lack high‐yielding cultivars that are tolerant to submergence at the vegetative stage. The present study was conducted to evaluate the submergence tolerance, yields and agronomic characteristics of improved submergence‐tolerant rice lines. Experimental lines combining short to intermediate stature (80–115 cm) with tolerance to submergence were developed from tall, lowyielding tolerant cultivars at the International Rice Research Institute Los Baňos, Philippines. Lines were selected based on high survival after submergence in concrete tanks and visual evaluation of yield potential in the field. These lines were tested in field and glasshouse tanks for survival after 10 to 13 d of submergence and were evaluated in replicated trials in the dry and wet seasons. Experimental lines selected for submergence tolerance from crosses with tolerant parents showed higher survival than lines not selected for tolerance in the field and glasshouse tests. The most tolerant lines showed low yield potential (≤4100 kg ha−1); however, one breeding line with high submergence tolerance (IR49830‐7‐1‐2‐2) yielded 4880 kg ha−1 and was among the highest yielding lines in the trial. This shows that submergence tolerance can be incorporated into improved, high‐yielding lines, which can raise productivity in submergence‐prone areas. Submergence tolerance may also be useful for systems in which rice is seeded directly into standing water, where deep water during crop establishment has been proposed as a means of suppressing weed growth.
Quantitative Trait Loci Controlling Resistance to Gray Leaf Spot in Maize
Authors: Bubeck D. M. , Goodman M. M. , Beavis W. D. , Grant D.
Published: July 2010

Gray leaf spot (GLS) (caused Cercospora zeae‐maydis Theon & Daniels) is a fungal disease of the maize (Zea mays L.) that can cause significant grain yield reductions. Quantitative resistance to GLS does exist; therefore, one method of controlling the disease is to develop hybrids with genetic resistance. The objective of this study was to identify quantitative trait loci (QTL) and type‐of‐gene action for GLS resistance in segregating families of three single‐cross populations of maize using restriction fragment length polymorphisms (RFLPs). We also attempted to determine the consistency of QTL over environments and populations. Population 1 (POP1) consisted of 139 F2:3 families evaluated in three environments. Population 2 (POP2) consisted 193 F2:3 families and Population 3 (POP3) had 144 F2:3 families; POP2 and POP3 were considered as replicate populations evaluated in separate environments. Families were rated for GLS on a plot basis by a scale of 1 (susceptible) to 9 (resistant), and ratings were taken at 5‐ to 18‐d intervals in each environment. The QTL were identified on the basis of marker associations with GLS means over all ratings taken in an environment, as well as a GLS mean over environments for POP1 and over POP2 and POP3 for the replicate populations. Based on single‐factor ANOVA, detectable individual markers accounted for 4 to 26% of the phenotypic variation. The QTL associated with GLS were inconsistent over environments, but the cause of these differences could not be determined. One region on chromosome 2 was associated with GLS resistance in POP1, POP2, and POP3. Additive gene action was displayed for nearly all markers associated with resistance.
Relationships among Early European Maize Inbreds: II. Comparison of Pedigree and RFLP Data
Authors: Messmer Monika M. , Melchinger Albrecht E. , Herrmann Reinhold G. , Boppenmaier Jürgen
Published: July 2010

Information on genetic relationships among genotypes is of great importance to breeders. In this study we analyzed 29 maize (Zea mays L.) inbreds (18 flint and 11 dent lines) from the European germplasm by means of pedigree and RFLP analyses. Our main objective was to compare Malécot's coancestry (f based on pedigree data with genetic similarity (GS) based on RFLP data of 188 clone‐enzyme combinations (CECs) for their ability to quantify the degree of relatedness among inbreds. Rank correlations between f and GS were highly significant (P < 0.01) for 87 related (f > 0) pairs of flint lines (rs = 0. 71) an for 30 related pairs of dent lines (rs = 0.86). One dent line was excluded because of likely errors in pedigree detected by RFLP data and confirmed by heterosis data. Based on linear regression of GS on f, coancestry explained 82 and 70% of the variation in GS for related pairs of flint and dent lines, respectively. Therefore, both the coancestry and marker approach are well‐suited to (i) measure the average level of relatedness and (ii) identify closely related lines. Observed deviations of GS from its regression on f for individual pairs of lines can be explained by (i) random genetic drift and selection causing unequal genomic contributions of the parents, (ii) random variation of GS estimates due to sampling of the genome by the CECs used, (iii) wide variation in the GS estimates of unrelated lines, and (iv) experimental errors. Provided the genome is sampled by an adequate number (> 100) of CECs, RFLP‐based GS estimates reflect more accurately the true genetic similarity of a given line pair than f.
Intraspecific Variation in Sensitivity to UV‐B Radiation in Rice
Authors: Barnes Paul W. , Maggard Sharon , Holman Steven R. , Vergara Benito S.
Published: July 2010

Twenty‐two cultivars of rice (Oryza sativa L.) from diverse origins were grown under greenhouse conditions and exposed to ultraviolet‐B radiation (UV‐B; 280‐320 nm) simulating a 5% reduction in stratospheric ozone in spring for the Philippines (14° N lat.) to evaluate growth and morphological responses to UV‐B. In comparison to controls that received no UV‐B, plants exposed to UV‐B exhibited significantly reduced dry matter production (total plant and shoot), shoot height, leaf blade length and total leaf area, increased number of tillers, and greater weight fractions in leaf blades and roots. For most cultivars, the relative effects of UV‐B on shoot morphology were greater than the effects on biomass production. The direction of the UV‐B effects were generally similar for all cultivars, however, there were significant differences among cultivars in the magnitude of the UV‐Binduced changes. Upland cultivars (IRAT104 and OS4) and two lowland cultivars commonly planted in the USA (Star Bonnet and Lemont) were found to be least affected by the UV‐B, whereas modern, high yielding, lowland cultivars developed in the Philippines (IR52, IR35546‐17‐33, and IR58) were found to be among the most sensitive to UV‐B. Our results indicate that in rice, as in other grasses, shoot morphology may be more responsive to solar UV‐B change than plant productivity. Intraspecific variation in morphological responses to UVB could contribute to differences among cultivars in susceptibility to UV‐B‐induced changes in competitive balance between rice and associated weeds of the rice agroecosystem.
Resistance in Stenotaphrum to the Sting Nematode
Authors: Busey Philip , Giblin‐Davis Robin M. , Center Barbara J.
Published: July 2010

Host resistance would be a valuable defense against the sting nematode, Belonolaimus longicaudatus Rau, a pathogen of many crops, including turfgrass. Sting nematode damage and host suitability were compared among diploid and polyploid Stenotaphrum genotypes. A time‐course experiment compared diploid (2n = 18) ‘FX‐313’ and polyploid (2n = 30) ‘FX‐10‘ St. Augustinegrasses [Stenotaphrum secundatum (Walter) Kuntze], planted in pots with 250 mL Margate fine sand (siliceous, hyperthermic Mollic Psammaquent). Nematode numbers were determined 42,84,126,168, and 210 d after inoculating with 50 sting nematodes per pot. Root and shoot dry weights and transpiration rate were compared with uninoculated pots of each grass. Sting nematode numbers increased more rapidly on FX‐313 than on FX‐10, reaching a maximum 2580 nematodes (adults plus juveniles) per pot of FX‐313, 84 d after inoculation, compared with 380 nematodes per pot of FX‐10. Root damage by sting nematodes was severe in FX‐313 but was minor in FX‐10. Sting nematode numbers and root dry weight of inoculated FX‐313 were essentially unchanging from 84 to 210 d after inoculation, which suggested possible nematode suppression due to nematode injury of roots. Transpiration rate, a nondestructive indicator of nematode effect, was reduced in inoculated FX‐313, compared with uninoculated controls, throughout 84 to 168 d after inoculation, while FX‐10 transpiration rate was not affected. While FX‐313 was susceptible to the sting nematode, FX‐10 was resistant through a mechanism of antibiosis. We subjected four polyploid and four diploid Stenotaphrum genotypes to the same procedure, but harvested 128 or 129 d after inoculation. Nematode numbers differed (P < 0.001) among genotypes, ranging from 980 per pot of FX‐313 to 140 per pot of FX‐10. Root dry weight of diploids was reduced 33% due to nematodes but polyploids showed no effect. Some good hosts such as pembagrass [S. dimidiatum (L.) Brongn] ‘FL‐2195’ showed little or no damage, thus may represent resistance through a mechanism of tolerance.
Heritabilities and Genetic Correlations of White Clover Clones Grown in Three Environments
Authors: Rowe D. E. , Brink G. E.
Published: July 2010

White clover (Trifolium repens L.) is commonly grown in a legume and grass mixture, but most selection for elite clones has been as spaced plants in monoculture. This study estimates (i) population parameters important to breeding white clover when grown with two different grasses or in monoculture, and (ii) the potential for improving yield of clover grown in grasses when selection is made in monoculture. Ramets of 47 randomly selected clones from Southern Regional Virus Resistant white clover germplasm were space‐planted and grown for 3 yr in three environments: in monoculture, in Tifton 44 hybrid bermudagrass (Cynodon dactylon (L.) Pens.), and in common bermudagrass. Plant spread, yield, and stolon branching were measured at four harvests. Compared with monoculture, competition with common and hybrid bermudagrass reduced clover yield 60 and 45%, respectively. Environment had variable effect on magnitude of heritability estimates, which were statistically significant for each trait in each environment (H = 58 to 72%) except yield in common bermudagrass. Genetic correlations between environments were significant for clover yield and plant spread. Predicted response to selection in grass was 12 to 31% more effective than selection in monoculture for yield and 71 to 90% more effective for plant spread. The selection for yield in hybrid bermudagrass to improve yield in common bermudagrass was predicted 30% more effective than direct selection. Selection in monoculture should improve performance with grasses, but clover yield will not be maximized until selection is completed in a grass environment.
Identification of Quantitative Trait Loci Controlling Days to Flowering and Plant Height in Two Near Isogenic Lines of Maize
Authors: Koester Ruth P. , Sisco Paul H. , Stuber Charles W.
Published: July 2010

The number of days from planting to flowering is a trait of interest to maize (Zea mays L.) breeders for its importance in selecting appropriate hybrid parents, and for its role in the utilization of unadapted germplasm. Using molecular marker technology, we were able to identify quantitative trait loci (QTLs) controlling days to flowering and two correlated traits, plant height and total leaf number, in two near isogenic lines (NILs). NC264 and B73G are shorter, earlier versions of SC76 and B73 respectively, developed by introgressing Gaspé Flint and selecting for early flowering through repeated backcrosses. The NILs were screened for introgressed chromosomal regions with restriction fragment length polymorphisms (RFLPs). Seven introgressed regions were identified in NC264 and two in B73G, with a specific chromosome 8 region maintained in both NILs. The introgressed regions were tested for their effect on flowering date and plant height in segregating F2 populations and F3 families developed from crosses between the original inbred and the NIL. The NC264 × SC76 F2 population was tested in both long and short‐day photoperiod environments. The RFLP analysis of the F2 individuals and F3 families identified major QTLs for days to flowering and plant height on chro mosomes 1, 8, and 10. Major QTLs for total leaf number were found on chromosomes 1 and 8. Single‐factor analysis of variance techniques were employed for all pairwise marker‐trait associations. Additive gene action predominated at all loci. The most significant effects were constant across environments, generations, and populations except for the region on chromosome 8, which was not significant in the shortday photoperiod environment. Thus, the maturity QTL on chromosome 8 may represent a photoperiod response element. Selective determination of genotype using only the top and bottom 10% of the phenotypic extremes to identify QTLs was as effective as analysis of the entire population for detecting the most significant marker‐trait associations.
Morphological Development and Anatomical Features of Wheat Seedlings as Influenced by Temperature and Seeding Depth
Authors: Huang Bingru , Taylor Howard M.
Published: July 2010

Temperature and seeding depth are two major factors influencing the early development of winter wheat (Triticum aestivum L.). The morphological and anatomical features were investigated for plants grown at seeding depths of 3, 6, and 9 cm and ambient temperatures of 10, 20, and 30 °C to determine the effects planting depth and temperature had on certain seedling properties important in seedling physiology. Planting at 6‐ and 9‐cm depths and at 10 °C significantly reduced seedling emergence rate, shoot and root dry weight, leaf area, and number of seminal and crown roots. Deep planting limited seminal root number to about three and increased subcrown internode length in all temperature regimes. Planting at 9‐cm depth and at 30 °C near surface temperature reduced effective xylem radius in the subcrown internode. It was concluded that the decreased seedling growth and xylem radius of the subcrown internode and associated hydraulic properties by deep planting depended strongly on the growing‐condition temperature, and was minimized at the optimal temperature (20 °C) for early development of wheat seedlings. Planting at a deeper depth and higher temperature has the potential of increasing hydraulic resistance of the subcrown internode for wheat seedlings.
Rapid Extraction and Analysis of Nonstructural Carbohydrates in Plant Tissues
Authors: Hendrix Donald L.
Published: July 2010

Considerable time is necessary to determine the nonstructural carbohydrates (i.e., glucose, fructose, sucrose, starch) in plant tissues and some methods used for this purpose lack specificity. Two steps in such assays typically occupy much of the assay time: sample drying and homogenization/centrifugation. A laboratory method was therefore developed to carry out such assays without either of these steps. The new method involved separation of the ethanol‐soluble carbohydrates from disks or slices of plant tissue with hot aqueous ethanol and the in situ conversion of starch to glucose by enzymes. The amount of ethanol‐soluble sugars and the glucose released from the tissue during the starch digestion were then determined in a microplate assay using an enzyme‐coupled colorimetric reaction which was highly specific for glucose. The two starch‐degrading enzymes (α‐amylase and amyloglucosidase) and short digestion times (1.5 h) utilized in this method were selected to quantitatively release glucose from the starch in these samples without digesting significant amounts of β‐glucans. Results obtained with this technique were found to compare favorably with those obtained by homogenization of cotton (Gossypium hirsutum L.) leaf tissue. Besides cotton, this method has been successfully used to analyze soluble carbohydrates from a variety of other plant species. By this method it is possible to analyze plant samples two to five times faster than methods which employ sample drying and homogenization.
Comparison of Selection Methods for Dry Bean Populations Derived from Crosses between Gene Pools
Authors: Beaver J. S. , Kelly J. D.
Published: July 2010

New approaches are needed to broaden the genetic base and improve the yield potential of large‐seeded red beans (Phaseolus vulgaris L.). The objectives of this research were to compare the effectiveness of two recurrent selection methods to develop indeterminate red‐seeded bean populations that yield more than determinate red‐seeded varieties. The original base population was produced from crosses between genotypes from the Andean and Middle American gene pools. The performance of the populations developed by recurrent selection was tested in field trials conducted over three growing seasons in Puerto Rico. Both recurrent selection with F2 evaluation and recurrent selection with F5 evaluation were successful in developing tropically adapted indeterminate bean populations having seed type and seed size suitable for the Caribbean. Recurrent selection with F5 evaluation produced a larger number of indeterminate populations with greater seed yields than the determinate check cultivars. The greater seed yield of these indeterminate populations was attributed to longer reproductive periods and a greater number of days to physiological maturity. Heterosis for seed yield, the large amount of segregation for seed type and agronomic traits, and the lack of evidence of a linkage between small‐seed size and erect, indeterminate plant architecture favor the use of recurrent selection with advanced generation evaluations to improve bean populations derived from different gene pools.
Removing Spatial Variation from Wheat Yield Trials: A Comparison of Methods
Authors: Stroup Walter W. , Baenziger P. Stephen , Mulitze Dieter K.
Published: July 2010

Most cultivar evaluation trials use blocked designs and are analyzed using classical analysis of variance; however, a standard analysis for blocked designs often does not adequately account for spatial variability. Recent advances in spatial statistics suggest that there are better alternatives. The primary objective of this research was to compare randomized complete block (RCB) analysis with two nearest neighbor adjustment (NNA) methods; a random field procedure was also examined, as another way to remove spatial variability. Yield data from three replicated breeding nurseries involving diverse adapted and unadapted germplasm, each grown at four locations in Nebraska during 1988–1989, were used for the comparisons. The NNA approach was superior for all nurseries at all locations, on the basis of lower coefficient of variation and greater ability to distinguish cultivar differences. For 9 of 12 trials, RCB cultivar means were highly correlated with NNA cultivar means, indicating that both procedures would identify similar elite lines. For three trials, however, the estimated cultivar yield and cultivar rank from RCB and NNA procedures were different, and so different lines would be selected. The random field analysis was applied to the trial for which the discrepancy between the RCB and NNA analysis was greatest; this yielded results similar to the nearest neighbor analysis. Our results suggest that spatial trends are common in Nebraska and compromise the accuracy and precision of standard analysis of blocked designs. Therefore, NNA or random field analysis should be used to improve the analysis of breeding trials.
Water‐Use Efficiency and Carbon Isotope Discrimination in Peanut under Water Deficit Conditions
Authors: Wright G. C. , Rao R. C. Nageswara , Farquhar G. D.
Published: July 2010

Because of its relationship with water‐use efficiency (W), carbon isotope discrimination in leaves (Δ) was proposed to be useful for identifying genotypes with greater water‐use efficiency. In this study we examined the relationship between W and Δ in four peanut (Arachis hypogaea L.) genotypes. The genotypes were grown in and around mini‐lysimeters embedded in soil and were subjected to two drought regimes, intermittent and prolonged water deficit conditions, by varying the irrigation timing and amount. Automated rain‐out shelters prevented any rain from reaching the experimental plots during the treatment period. The mini‐lysimeters allowed accurate measurement of water use and total dry matter (including roots) in a canopy environment. Water‐use efficiency, which ranged from 1.81 to 3.15 g kg−1, was negatively correlated with Δ, which ranged from 19.1 to 21.8%. Tifton‐8 had the highest W (3.15 g kg−1) and Chico the lowest (1.81 g kg−1, representing a variation in W of 74% among genotypes. Variation in W arose mainly from genotypic differences in total dry matter production rather than from differences in water use. It is concluded that δ is a useful trait for selecting genotypes of peanut with improved W under drought conditions in the field. A strong negative relationship existed between W and specific leaf area (SLA, cm3 g−1) and between Δ and SLA, indicating that genotypes with thicker leaves had greater W. SLA could therefore be used as a rapid and inexpensive selection index for high W in peanut where mass spectrometry facilities are not available.
Effects of Intraspecific Interference on Maize Leaf Azimuth
Authors: Girardin Ph. , Tollenaar M.
Published: July 2010

Interception of solar irradiation by leaf canopies is influenced by the canopy architecture of crops, which is a function of shape, distribution, and orientation of the leaves that constitute the canopy. The objective of this study was to test the hypothesis that leaf azimuthal distribution in a maize (Zea mays L.) canopy is not influenced by plant density and row width. Experiments were conducted at Elora, Ontario, with maize grown at 4, 7, and 10 plants m−2 at a 0.76‐m row width in 1991 and 1992 and with maize grown at 7 and 10 plants m−2 at a 0.5‐m row width in 1992. Leaf orientation was recorded in 16 azimuthal classes for leaves from the bottom to the topmost leaf position. Results showed that the orientation of leaves in the topmost layer (twelfth to sixteenth leaf) was more perpendicular to the row for high than for low plant densities. An azimuthal shift of leaves from the bottom to the top in maize plants was apparent in all canopies, but the shift was larger for plants grown at high plant densities than for those grown at low plant densities and a similar trend was apparent for the comparison of maize grown at 0.76‐m vs. 0.5‐m row widths. Results of this study suggest that the orientation of leaves in a maize canopy is altered by intraspecific interference, thereby more effectively intercepting incident solar irradiance.