bluuebunny/crossref_metadata_2025 huggingface dataset:
A Third Allele at the Soybean dt1 Locus
Authors: Thompson Jeffrey A. , Bernard Richard L. , Nelson Randall L.
Published: July 2010

Two loci (Dt1 and Dt2) affect stem termination in soybean [Glycine max (L.) Merr.]. Both of these alleles have been backcrossed into near‐isogenic lines (hereafter referred to as isolines) of the indeterminate cv. Clark (Dt1Dt1 dt2dt2). The semi‐determinate isoline (Dt1Dt1 Dt2Dt2) is ≈ 75% the height of Clark and the determinate isoline (dt1dt1 dt2dt2) is ≈ 50% as tall as Clark. Recently, determinate Clark isolines have also been developed with the cv. Peking and Soysota as donor parents. These lines were similar in height to the semi‐determinate isoline. The objective of this research was to determine the genetic control of this new phenotype. The gene controlling the tall determinate phenotype was found to be identical in Peking and Soysota and allelic to dt1 The gene symbol dt1‐t has been approved by the Soybean Genetics Committee. Several leaf and stem characters were studied in the stem termination isolines. Although dt1‐tdt1‐t and Dt2Dt2 phenotypes are similar in plant height, dt1‐tdt1‐t is more similar to dt1dt1 when considering leaf and stem traits at the top of the plant.
Triple Testcross Analysis to Detect Epistasis in Maize
Authors: Wolf Duane P. , Hallauer Arnel R.
Published: July 2010

Maize (Zea mays L.) breeders have successfully exploited heterosis by crossing inbred lines to develop hybrids. Epistatic effects can contribute to the expression of heterosis for specific hybrids. The hybrid B73 × Mo17 was a widely grown hybrid with exceptional performance in the central U.S. Corn Belt during the late 1970s and early 1980s. The objective of this study was to determine if epistatic effects contribute significantly to the performance of B73 × Mo17. With use of the triple testcross design, 100 random F2 plants from B73 × Mo17 were testcrossed to B73, Mo17, and their F1. The 300 testcrosses were evaluated at three locations in 1992 and two locations in 1993. Triple testcross analysis suggested that epistatic effects were important for ear length, number of kernel rows, ear height, and flowering traits. In the analysis of variance, additive by additive effects were not significant for grain yield, whereas additive by dominance and dominance by dominance effects were significant. The additive by additive by environment interaction was more important than additive by additive effects per se for grain yield. Epistatic deviations from the comparison of testcross means suggest that B73 had favorable additive by additive effects for grain yield, barren plants, kernel‐row number, ear height, and silk delay. Inbred Mo17 had favorable additive by additive effects for ear length. The presence of significant positive epistatic effects may have contributed to the expression of heterosis and could explain why B73 × Mo17 was an exceptional and widely grown hybrid.
Physiological Correlates of Variation in Nitrogen‐Use Efficiency in Two Contrasting Sugarcane Cultivars
Authors: Ranjith Subasinghe A. , Meinzer Frederick C.
Published: July 2010

The efficiency of N utilization in photosynthesis and dry matter production (NUE) is an important crop performance criterion. Our objectives were to characterize the magnitude and physiological correlates of variation in NUE in the C4 grass, sugarcane (Saccharum spp. hybrid). Two genotypes known to differ with regard to their resistance to drought and salinity stress were grown in solution culture in a glasshouse at three levels of N availability (0.1, 1.0, and 10 mM N). Photosynthetic gas exchange, dry matter accumulation, carboxylase activity, chlorophyll content, leaf N status, and plant‐water relations characteristics were evaluated. Leaf water potential and plant hydraulic conductance decreased as applied N was reduced from 10 to 0.1 mM. At a given leaf N status, NUE was always significantly higher in the stress‐resistant genotype (H69‐8235) than in the susceptible genotype (H65‐7052). However, a large genetic difference in dry weight accumulation at a given level of external N supply was observed only at 10 mM applied N. Higher NUE in H69‐8235 was strongly associated with greater relative partitioning of leaf N to chlorophyll and ribulose 1,5‐bisphosphate carboxylase‐oxygenase (Rubisco). The fraction of leaf N partitioned to the photosynthetic apparatus increased with declining N content in both genotypes. Photosynthetic and dry matter‐based NUE were not entirely consistent with each other because growth was more sensitive than photosynthesis to N stress. It may be possible to further improve the already high NUE of C4 grasses by screening genotypes for differences in partitioning of leaf N into components of the photosynthetic apparatus such as chlorophyll and Rubisco.
QTL Mapping in Testcrosses of European Flint Lines of Maize: I. Comparison of Different Testers for Forage Yield Traits
Authors: Lübberstedt Thomas , Melchinger Albrecht E. , Schön Chris C. , Utz H. Friedrich , Klein Dietrich
Published: July 2010

In the cooler temperate regions of the world, maize (Zea mays L.) is primarily cultivated for forage usage. In this study, we mapped and characterized quantitative trait loci (QTL) affecting testcross performance of important forage maize traits and investigated their consistency across environments and testers. Two elite flint inbred lines were crossed to generate 380 F2 individuals, 345 of which were genotyped at 89 RFLP (restriction fragment length polymorphism) marker loci. The 380 F3 lines obtained by selfing the F2 individuals and the parent lines were crossed to two diverse dent inbred testers. Each series of testcrosses (TC) was evaluated in field trials with two replicates in five environments. Five traits were analyzed: dry matter yield (DMY), dry matter concentration (DMC), plant height (PHT), starch concentration (STC), and starch yield (STY). Genotypic (
) and genotype × environment variances were highly significant for all traits in both TC series. Heritabilities ranged from 0.64 to 0.88 except for STY (0.46, 0.47). Genotypic correlations between testers were high (>0.80) for all traits. QTL analyses were performed by composite interval mapping. Between seven (STY) and 16 (PHT) QTL were detected in each testcross series, explaining between 52 and 71% of all in a simultaneous fit. Few QTL displayed significant interactions with environments. Results were highly consistent across testers for DMC and PHT, but not for DMY, STC, and STY. Although a comparison of TC generation means indicated significant epistasis for DMY and PHT, significant interactions between QTL were detected in two cases only. If a genomic region simultaneously affected two characters, the increasing alleles for the individual traits originated in most cases from the same parent for positively correlated traits and from different parents for negatively correlated traits.
RAPD Markers Linked to Three Major Anthracnose Resistance Genes in Common Bean
Authors: Young Roberto A. , Kelly James D.
Published: July 2010

Durability of the resistance to anthracnose, caused by Colletotrichum lindemuthianum (Sacc. & Magnus) Lambs.‐Scrib., could be increased if more than one resistance gene were incorporated into current bean (Phaseolus vulgaris L.) cultivars. The objective of this study was to identify random amplified polymorphic DNA (RAPD) markers linked to three independent resistance loci to facilitate gene pyramiding in common bean. Markers were identified by means of bulked segregant analysis and heterogeneous inbred populations. RAPD marker OF10530 cosegregated in repulsion‐phase (1.9 ± 1.4 cM) with the Co‐1 (A) allele. A survey of diverse bean genotypes showed that the OF10530 RAPD band could facilitate introgression of the Co‐1 gene across the Andean and Middle American Phaseolus gene pools. RAPD marker OAB3450 was linked in coupling‐phase (5.9 ± 1.7 cM) to the Co‐5 (Mexique 3) allele. A coupling‐phase (OAH1780) and repulsion‐phase (OAK20890) RAPD marker were linked to the Co‐6 locus. These markers flanked the Co‐6 locus and mapped at 12.3 ± 1.9 from the Co‐6 allele and at 7.3 ± 1.5 cM from the co‐6 allele, respectively. Coupling and repulsion‐phase RAPD markers used as a codominant pair showed a higher selection efficiency (95%), for the identification of homozygous (Co‐6 Co‐6) F2 individuals, than individual selection either for a coupling‐phase (33%) or against a repulsion‐phase (92%) RAPD phenotype. Durability of resistance to anthracnose could be improved if (i) two major resistance genes were pyramided by marker assisted selection, (ii) different genes were deployed in different regions, and (iii) resistance genes from different gene pools were combined.
Mapped Clone Sequences Detecting Differences among 28 North American Barley Cultivars
Authors: Dahleen Lynn S.
Published: July 2010

Genetic linkage maps of molecular markers have been developed for barley (Hordeum vulgare L.) to aid development of improved barley cultivarso However, crosses between genetically diverse parents used to maximize polymorphism in map construction are not appropriate for use in breeding programs for cultivar development. The objective of this study was to determine whether the amount of genetic variation detected at RFLP (restriction fragment length polymorphism) marker loci among 28 North American spring barley cultivars was sufficient to permit molecular marker‐assisted selection in North American barley breeding programs. DNA extracted from these cultivars was restriction digested with BamHI and hybridized to 100 done sequences mapped by the North American Barley Genome Mapping Project. A diversity index (DD was calculated for each clone sequence based on the number and frequency of RFLP patterns detected. Fifty‐seven of the clones detected RFLPs among these cultivars. Twenty‐nine of these were highly informative (DI>0.500) in detecting differences among the 28 cultivars. Clone sequences were identified that separated the 28 cultivars by geographic origin (Western vs. Midwestern) and by spike morphology (two‐rowed vs. six‐rowed). While 47% of the clone sequences detected RFLPs among the 15 Midwestern six‐rowed cultivars, only 17% detected RFLPs among the currently grown cultivars Robust, Excel, Foster, and Stander. The RFLP loci that differ between these cultivars appear to be associated with quantitative trait loci (QTL) for agronomic and malt quality traits. Molecular marker‐assisted selection in malting barley breeding programs can be used to select the optimal alleles at these QTL and to incorporate qualitative traits such as disease resistance from less adapted germplasm.
Designation of a New Greenbug, Biotype K, Injurious to Resistant Sorghum
Authors: Harvey T. L. , Wilde G. E. , Kofoid K. D.
Published: July 2010

A sorghum [Sorghum bicolor (L.) Moench] line, ‘PI 550610’, resistant to Biotype I greenbug [Schizaphis graminum (Rondani)] was susceptible to greenbugs collected in Haskell County, KS, in 1992. This isolate is designated Biotype K. It maybe of considerable economic importance because of its virulence to PI 550610, which is being used widely in breeding programs to develop sorghum hybrids resistant to Biotype I greenbugs. The other sources of resistance to Biotype I, ‘PI 266965’, ‘PI 1550607’, and ‘Cargill6 07E’, showed at least some resistance to Biotype K. PI 266965, derived from Sorghum halepense L., maintained the highest level of resistance to Biotype K. However, this tetraploid is not currently useable in breeding programs. In addition, 12 sorghum lines resistant to Biotypes C and E were susceptible to Biotype K. Thus, PI 550607 and ‘Cargill 607E’ are the only known sources tested that resist Biotype K, but the level of resistance in these genotypes needs further evaluation. The multigenic greenbug resistance of hybrids such as Cargill 607E may be more durable in the field than resistance based on a single gene. Although Biotype K was discovered before the existence of selection pressure from hybrids resistant to Biotype I, the potential for Biotype K to replace Biotype I would be enhanced by the use of hybrids derived from PI 550610 which are resistant to Biotype I but susceptible to Biotype K. Greenbug resistance to Biotype I in the small grains [wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), and rye (Secale cereale L.] remained effective against Biotype K. Since the small grains are resistant to both biotypes their use in the field probably would not effect the status of Biotype K relative to Biotype I.
RAPD Analysis of South Pacific Coconut Palm Populations
Authors: Ashburner G. R. , Thompson W. K. , Halloran G. M.
Published: July 2010

The South Pacific region represents a large potential genetic resource for improvement of coconut palms (Cocos nucifera L.). A study of the genetic diversity in the species was made in 1992–1993 by means of RAPD analysis on a representative sample from 17 distinct South Pacific coconut populations to characterize the germplasm present in the region. A moderate level of genetic diversity was found, although very few RAPD markers were unique to specific populations. Approximately 60% of the observed diversity occurred within‐populations, but this level varied between the various populations. This indicated the generally low but variable influence of gene migration between populations, the establishment of populations by few individuals that comprised a fraction of the genetic variation of their parental populations (founder effects), and subsequent selection by the local human population. Although the coconut populations of the region generally displayed a pattern of continuous variation, this continuum could be divided into discrete groups by cluster analysis. This division comprised a southern group of populations, a northern‐eastern group, and singlepopulation groups from the Marquesas and Hawaii groups. The population from Rennell Island diverged from the main genetic continuum, apparently because of isolation and artificial selection. Collection and conservation strategies have been devised for coconut germplasm in the South Pacific region based on existing genetic diversity.
Striga hermonthica Seed Inoculum Rate Effects on Maize Hybrid Tolerance and Susceptibility Expression
Authors: Kim Soon‐Kwon , Adetimirin Victor O.
Published: July 2010

A parasitic plant, Striga hermonthica (Del.) Benth., infests millions of hectares of arable land in sub‐Saharan Africa, and it threatens production of major cereal crops including maize (Zea mays L.). Erratic natural infestation is considered a major constraint to assess host plant resistance to the parasite. The objective of this study was to evaluate the effects of different S. hermonthica seed inoculum rates on a tolerant and a susceptible maize genotype. Individual maize plants of the tolerant (8322‐13) and the susceptible maize hybrid (8338‐1) were inoculated with six rates of germinable Striga seeds: 750, 1500, 2250, 3000, 3750, and 4500. Uninfested plots served as the control. The experiment was conducted at two locations, Mokwa (two seasons) and Abuja (one season), in Nigeria. Increasing Striga inoculum level increased Striga emergence and the amount of damage to the host plant, plant height, and grain yield of the host crop. The tolerant hybrid showed less host plant damage (P < 0.01) and that fewer S. hermonthica plants emerged (P < 0.05) than the susceptible hybrid. Among the four traits studied, host plant damages core was most correlated with grain yield (r = −0.65**). Average grain yield of the tolerant hybrid, 8322‐13, was 97% higher than that of the susceptible hybrid, 8338‐1, across the six inocolum rates. The tolerant hybrid produced similar grain yields under all levels of the inoculum; the yield reductions ranged from 27% (2250 seeds) to 35% (4500 seeds), while the yield reduction of the susceptible hybrid ranged from 43% (750 seeds) to 74% (3750 seeds). Based on the results this study, we conclude that host plant tolerance is the key element for stabilizing crop yield under S. hermonthica infestation.
The Effect of Rbs2 on Yield of Soybean
Authors: Bachman M. S. , Nickell C. D. , Stephens P. A. , Nickell A. D. , Gray L. E.
Published: July 2010

Brown stem rot (BSR), caused by Phialophora gregata (Ailington & Chamberlain) W. Gams, is a vascular‐foliar soybean [Glycine max (L.) Merr.] disease of the north central USA. Although yield comparisons have been made between susceptible and resistant lines, no study has evaluated yield differences between near‐isogenic lines differing in brown stem rot reaction. The objective of this study was to compare brown stem rot resistant and brown stem rot susceptible near‐isogenic lines for yield and other agronomic traits. In this study, five pairs of near‐isogenic lines for the Rbs2 resistance gene were grown at six locations in Illinois in 1994 and nine locations in Illinois in 1995, relying on natural infection with P. gregata. Near‐isogenic lines were evaluated for disease incidence (percentage of plants exhibiting brown stem rot foliar symptoms) and disease severity (degree of foliar chlorosis‐necrosis) in late August and harvested in September and October. At seven locations with 13% or greater incidence of brown stem rot, a 10.6% yield advantage was associated with the resistance gene, Rbs2. At eight locations with less than 3% incidence of brown stem rot, there was no yield difference between resistant and susceptible near‐isogenic lines. These results indicate that Rbs2 prevents yield loss in the presence of brown stem rot.
Genotype and Environmental Effects on Natto Soybean Quality Traits
Authors: Cober E. R. , Frégeau‐Reid J. A. , Pietrzak L. N. , McElroy A. R. , Voldeng H. D.
Published: July 2010

Production of small‐seeded natto soybean [Glycine max (L.) Merr.] has increased in eastern Canada during the past decade. Improved natto quality characteristics are important for maintaining and increasing this market. This study was conducted to examine environmental and genotype × environment effects on quality characteristics. Two data sets were used for statistical analysis: seven lines grown at five locations in 1989 and 1990 (Data Set 1) and fifteen lines grown at the same five locations in 1993 and 1994 (Data Set 2). Quality characteristics important in natto production were measured: smallseed fraction, percentage of seeds with impermeable seed coats, water uptake, seed shape, and levels of the seed constituents, Ca, oil, and sugar. Genotypes were significantly different for most traits in both data sets. Location effects were not significant for any quality traits. Year effects were significant only for seed shape and sugar levels in Data Set 2. Year × location interactions were often significant, but no patterns were apparent in these interactions. Genotype × environment interactions were often significant, but these variance components were usually an order of magnitude smaller than the main effects of genotype. These results indicate that it is possible to develop natto soybean cultivars that are broadly adapted to the short‐season areas of eastern Canada.
Effect of Radiation Environment on Radiation Use Efficiency and Growth of Sunflower
Authors: Bange M. P. , Hammer G. L. , Rickert K. G.
Published: July 2010

The level of incident radiation and the proportion of radiation that is diffuse affects radiation use efficiency (RUE) in crops. However, the degree of this effect, and its importance to growth and yield of sunflower (Helianthus annuus L.) have not been established. A field experiment was conducted to investigate the effects of radiation environment on RUE, growth, and yield of sunflower. A fully irrigated crop was sown on an alluvial‐prairie soil (Fluventic Haplustoll) and was exposed to three distinct radiation environments. In two treatments, the level of incident radiation was reduced by 14 and 20% by suspending two different types of polyethylene plastic films well above the crop. In addition to the reductions in incident radiation, the proportion of radiation that was diffuse was increased by about 14% in these treatments. Lower incident radiation and increased proportion of diffuse radiation had no effect on total biomass, phenology, leaf area, and the canopy light extinction coefficient (k = 0.89). However, yield was reduced in shaded treatments due to smaller grain size and lower harvest index. Although crop RUE measured over the entire crop cycle (1.25 g/MJ) did not differ significantly among treatments, there was a trend where RUE compensated for less intercepted incident radiation. Theoretical derivations of the response of RUE to different levels of incident radiation supported this finding. Shaded sunflower crops have the ability to produce biomass similar to unshaded crops by increasing RUE, but have lower harvest indices.
Is Seedling Root Morphology Predictive of Seasonal Accumulation of Shoot Dry Matter in Maize?
Authors: Richner W. , Kiel C. , Stamp P.
Published: July 2010

Seedling vigor at suboptimal temperatures is an important characteristic in maize (Zea mays L.) growth in cool regions. Selection for improved vegetative growth and seasonal dry matter accumulation at suboptimal temperatures would be more efficient if seedling traits related to field performance could be identified under controlled conditions. This study evaluated if root traits of seedlings grown at cool or warm temperature regimes are predictive of early growth and silage yield in the field. Twenty early‐ to medium‐late maturing European hybrids (FAO maturity ratings 200–280) were grown in a solid substrate until the third leaf stage under two controlled temperature regimes (25/22.5°C and 15/12.5°C, day/night) and until silage maturity in three field environments on a Orthic Luvisol soil in Central Germany. The closest relationships with early field growth were found for the total length of the main roots (r = 0.65, P < 0.01) and total length (r = 0.60, P < 0.01) and number (r = 0.68, P < 0.01) of firstorder laterals of the seminal roots at 25122.5°C. Silage yield was best correlated with the branching density of the seminal roots (r= 0.66, P < 0.01) at 15112.5°C and the total root surface area (r = 0.58, P < 0.01) at 25122.5°C. These root traits could potentially be used only in combination with other secondary characters for the indirect selection for shoot performance because individual root traits explained less than 50% of the variation in shoot weight in the field. Negative correlations between the chilling stability of most seedling traits, as expressed by the relative difference of trait means at 15/12.5°C and 25122.5°C, and silage yield indicated that chilling‐tolerant genotypes may be less capable of benefiting from the warmer temperatures during later growth stages.
Chilling Tolerance during Emergence of Cowpea Associated with a Dehydrin and Slow Electrolyte Leakage
Authors: Ismail A. M. , Hall A. E. , Close T. J.
Published: July 2010

Seeds of annualw arms eason crops are sensitive to chilling temperatures during emergence often encountered during spring sowings in subtropical regions. Mechanisms for genotypic differences in emergence of cowpea [Vigna unguiculata (L.) Walp.] seedlings were investigated under chilling field and controlled growth chamber conditions. Rate of emergence was slower and extent of maximal emergence was less under chilling (15°C) compared with more favorable (28°C) temperatures. Under chilling conditions, deeper sowing (7.5 vs. 2.5 cm) resulted in slower as well as less maximal percentage emergence. Reducing seed moisture content to 50 g kg−1 resulted in decreased percentage emergence and faster electrolyte leakage from seeds compared with seeds at moisture contents of 120 and 150 g kg−, which had similar emergence. In all studies under chilling conditions, cowpea line 1393‐2‐11 consistently attained greater maximal percentage emergence than the genetically similar line 1393‐2‐1. A 35‐kDa dehydrin protein [late embryogenesis abundant (LEA) D‐11 family] was found in 1393‐2‐11 seeds that was absent in 1393‐2‐1, and leakage of electrolytes during seed imbibition at low temperature was slower from 1393‐2‐11 seeds. Studies with reciprocal hybrids indicated nuclear inheritance and a dominant effect for the gene controlling the presence of the dehydrin, and a maternal effect on the extent of electrolyte leakage from seeds at chilling temperature. An additive model was developed for the dependence of the chilling tolerance of 1393‐2‐11 on the presence of the dehydrin (positive nuclear effect) and the extent of electrolyte leakage from seeds (negative maternal effect), which accounted for 96% of the variation between observed and calculated percentage emergence values of the hybrids.
Low Temperature Tolerance Assessment in Paspalum
Authors: Cardona C. A. , Duncan R. R. , Lindstrom O.
Published: July 2010

The plant survival of three ecotypes of seashore paspalum (Paspalum vaginatum Swartz) submitted to freezing temperatures was evaluated by two methods: electrolyte leakage and freeze shock‐recovery. Bermudagrass [Cynodon dactylon (L.) Pets. cv. Midiron] was used as a check. Acclimated and nonacclimated plants were evaluated from 1994 to 1995 in Georgia by both methods to compare their performance. Results indicated that seashore paspalum was slower to acclimate than Midiron bermuda under the treatment conditions used in this experiment. However, a significant acclimation effect was found in HI‐1 paspalum, indicating the presence of variability for this trait within the species. The LT50 determinations demonstrated the superior cold hardiness of Midiron compared with seashore paspalum. Among the paspalum ecotypes, HI‐1 ranked superior to Adalayd and PI 299042, respectively, when plants were acclimated (AC). When nonacclimated (NA), Adalayd ranked superior to the other two ecotypes. These genotypic rankings were consistent for both methods of evaluation, indicating their effectiveness for efficiently screening cold hardiness responses among multiple ecotypes. Electrolyte leakage curves indicated that the lethal electrolyte leakage levels for AC and NA paspalum ecotypes were similar. Additional studies are required to evaluate the mechanism present in HI‐l, which showed significant acclimation effects on plant survival.
Relationship between Genetic Distance among Parents and Genetic Variance in Populations of Soybean
Authors: Kisha T. J. , Sneller C. H. , Diers B. W.
Published: July 2010

A major goal of soybean [Glycine max (L.) Merr.] breeding is the development and identification of high yielding transgressive segregants. Populations that have greater genetic variations should, on average, have more transgressive segregants than populations with lesser variance. The goal of this research was to study whether the genetic distances between parents of crosses were predictive of which crosses have the greatest genetic variance for yield and other agronomic traits. Genetic variance for seed yield, plant height and maturity date was estimated for three sets of populations in field tests. The first set included eight populations evaluated in 1989 and 1990, the second set included 21 populations evaluated in 1993 and a subset of 13 populations evaluated in 1994, and the third set included 24 populations evaluated in 1994 and a subset of 10 populations evaluated in 1995. The parents of the crosses were evaluated with RFLP markers to estimate RFLP distances (RFD) and for coefficient of parentage (CP) which was subtracted from one to measure genealogical distances (GD). Both GD and RFD were significantly (P < 0.05) correlated with genetic variance for plant height for the first set. There were no significant correlations between either genetic distance estimator and genetic variance for any trait in the second set. In the third set, GD was significantly correlated with maturity and plant height and RFD was significantly correlated with maturity. Genetic variance for yield was adjusted for maturity with covariance analysis. These adjustments reduced the estimates of yield variance and mostly reduced the correlations between yield variance and genetic distance estimates. To further evaluate the predictive ability of GD and RFD, the populations in each set were subdivided in to two groups, one with parents that had the greatest genetic distance and the other with the least distance based on GD or RFD. The average genetic variance for yield of populations in the more distant group was greater than for the less distant group for the first and third set. These differences were significant for the third set in both years for RFD. These results indicate that although genetic distance can not accurately predict genetic variance of individual crosses, it can on average be useful to identify groups of crosses that will produce populations with greater genetic variance
Backcrossing a Complex Black Seed Trait from Diploid into Tetraploid Alfalfa Avoids the Complexities of Tetrasomic Inheritance
Authors: Kimbeng C. A. , Bingham E. T.
Published: July 2010

Black seed in alfalfa (Medicago sativa L.) may be useful as a seed marker and for pigmentation studies. The trait is controlled by three to four genes. Normal alfalfa seeds with tan coats have a dominant inhibitor of the black trait. Black seeds appear to be conditioned by a homozygous recessive allele at the inhibitor locus and a dominant allele for pigments at each of two or more additional loci. The complexity of the trait makes its manipulation inefficient at the tetraploid level. In this study, 2n eggs of diploid alfalfa plants with black seed coats were used to transfer the trait to the tetraploid level. Five blackseeded diploid plants were used as female parents and crossed with random pollen from a select group of adapted tetraploid plants. Twenty‐one tetraploid hybrids were identified in the first cross. All of the hybrids had tan seed coats. Each tetraploid hybrid was backcrossed as a pollen parent to an unrelated (crisscross backcross) blackseeded diploid plant to minimize inbreeding depression. Of the thirty tetraploid backcross hybrids produced, four were black‐seeded, vigorous, and fertile. The four black‐seeded tetraploids were used in another cross and backcross to transfer the trait to adapted cultivars and produce desired amounts of black seed. Although the blackseeded trait has a complex inheritance pattern, it was transferred to the tetraploid level with minimum effort. Alternative procedures would have required chromosome doubling or finding the trait in extremely large segregating populations at the tetraploid level.
Modification and Uses of Endophyte‐Enhanced Turfgrasses: A Role for Molecular Technology
Authors: Bacon C. W. , Richardson M. D. , White J. F.
Published: July 2010

Over the past decade, the significance of symbiotic fungal endophytes in turfgrasses was established as having the potential for supplementing the genetics of turfgrass improvement since endophyte‐infected grasses frequently show enhanced performance. Endophyte‐enhanced traits include insect and mammalian deterrence to herbivory, and often increased tolerance of drought and other abiotic stresses. However, not all endophytes are suited for use in enhancing grass performance, and only those fungi that are symptomless endophytes of grasses are currently being used. The endophytes that are of the major focus for current use include species of Neotyphodium (=Acremonium), e.g., N. coenophialum, N. lolli, and other species of Neotyphodium. The Neotyphodium endophytes do not reproduce sexually, and only produce conidia under laboratory culture, suggesting that they should be genetically stable. These endophytes can be removed from the host, transformed by molecular technology, and reinserted into the host. However, these fungi have other means for genetic variation, which might include chromosome polymorphisms, altered chromosome structures, and loss of nonessential chromosomes. Thus, the genetics related to an endophyte‐enhanced trait of that turfgrass might not be stable. However, the potential for genetic engineering of the endophytes is growing nearer with recent application of DNA mediated techniques. Furthermore, genetic engineering or other approaches may soon lead to endophyte‐grass associations that have further enhanced fitness or are more benign to wildlife. Before such genetically modified systems are marketed, particular attention and extensive field tests should be applied to ensure that they retain their beneficial characteristics and have truly acquired their intended improvements. Continued research into the biochemical and genetics basis of endophyte‐enhanced traits should eventually identify genes that ultimately can be use for the production of transgenic grasses.
Breeding for Drought Resistance in Rice: Physiology and Molecular Genetics Considerations
Authors: Nguyen Henry T. , Babu R. Chandra , Blum A.
Published: July 2010

Drought stress is a major constraint to rice (Oryza sativa L.) production and yield stability in many rainfed regions of Asia, Africa, and South America. The genetic improvement of adaptation to drought is addressed through the conventional approach by selecting for yield and its stability over locations and years. Because of low heritability of yield under stress and inherent variation in the field, such selection programs are expensive and slow in attaining progress. The objective of this paper is to review the current knowledge in physiology and molecular genetics which have implications in breeding for drought resistance in rice. The ability of root systems to provide for evapotranspirational demand from deep soil moisture and capacity for osmotic adjustment are considered major drought resistance traits in rice. However, selection for these traits still entail extensive investments in field nurseries or greenhouse facilities and is prone to problems of repeatability because of environmental variability. Recent development of molecular linkage maps of rice and other advances in molecular biology offer new opportunities for drought resistance breeding. Molecular markers linked to root traits and osmotic adjustment are being identified, which should lead to marker‐assisted selection. Transgenic rice plants having tolerance to water deficit and osmotic stresses have been reported. Work on genetic engineering of osmoprotectants, such as proline and glycine betaine, into the rice plant for drought tolerance improvement is in progress. Close collaboration between molecular geneticists, plant physiologists, and breeders is needed to critically assess the contribution of specific genes and application of molecular genetics to breeding for drought resistance in rice and other crops.
Comparison of Obsolete and Modern Cotton Cultivars at Two Nitrogen Levels
Authors: Meredith William R. , Heitholt J. J. , Pettigrew W.T. , Rayburn S.T.
Published: July 2010

Increase in cotton (Gossypium hirsutum L.) yields have been the result of both improved crop management and breeding. However, there is little information on how both management and breeding have interacted to produce higher yields. The objective of this study was to determine to what degree yield improvements and maturity changes which have taken place in the last 54 yr are due to using higher N rates and new cultivars. Eight modern cultivars (MC) and eight obsolete cultivars (OC) were grown on two soil types near Stoneville, MS, in 1992 and 1993. The year of cultivar release ranged from 1938 to 1992. Two N rates of 22 and 112 kg ha−1 were used. The field design was a randomized complete block with five replications. Five hand harvests were made on all tests to measure yield and maturity differences. A significant N × cultivar interaction was detected. The average yield for MC was 914 and 1021 kg ha−1 for the low and high N rates, respectively, or a 12% increase. However, average yield for OC was 743 and 799 kg ha−1, respectively, or an 8% increase. The slope of the equation predicting yield from year of cultivar release was 6.1 and 4.8 kg ha−1 yr−1 for the 112 and 22 kg ha−1 N rates, respectively. The higher N rate resulted in a 4‐d delay in maturity, measured as days after planting (DAP) until 65% of the crop was harvestable. The maturity range for MC was 6 d, ranging from 136 to 142 DAP. The range for OC was three d, 138 to 141 DAP. Cultivar × environment interactions were small. This study shows that high yields can be obtained with both late and early maturity cultivars. However, early maturing culfivars escape some late season insect buildups and allow for greater harvesting flexibility. The regression coefficient of yield increase on year of release was significantly lower in this study than that detected in two previous studies.
Dry Matter Partitioning in Groundnut Exposed to High Temperature Stress
Authors: Wheeler T. R. , Chatzialioglou A. , Craufurd P. Q. , Ellis R. H. , Summerfield R. J.
Published: July 2010

The yield of groundnut (Arachis hypogaea L.) grown in West African environments is often limited by high temperatures. We tested whether or not differences in the tolerance of groundnut genotypes to high temperature episodes are due to genotypic differences in the rates of dry matter partitioning to yield. A high temperature tolerant (HIT) and a high temperature sensitive (HTS) genotype were grown in a polyethylene‐covered greenhouse (polytunnel) at 30/25°C (day/night) until after the start of pegging (49 d after planting, DAP). Then, cohorts of each genotype were exposed for 6 d to four different constant day temperatures between 30 and 50°C before returning to the common environment until harvest maturity (98 DAP). Total plant biomass and seed yield at 98 DAP were reduced by the hottest temperature episodes and were less in the HTS compared with the HIT genotype. Proportional reduction in biomass and seed yield due to high temperature stress was greater in the HTS than the HTT genotype. The root/total biomass ratio declined more rapidly after flowering in the HTS compared with the HTT genotype. The start of seed‐filling was delayed by progressively hotter temperature episodes and was 11.7 d later in the HTS than the HTT genotype. However, the rate of increase in seed harvest index during seed filling was 0.0068 d−1 for both genotypes and was not affected by high temperature stress. We conclude that genotypic differences in the response of groundnut yield to episodes of high temperature stress were due to differences in the timing of seed filling rather than to genotypic differences in the rate of dry matter partitioning to fruits.
Forage Quality and Alfalfa Characteristics in Binary Mixtures of Alfalfa and Bromegrass or Timothy
Authors: Spandl E. , Hesterman O. B.
Published: July 2010

Seeding a perennial grass with alfalfa (Medicago sativa L.) may provide benefits without significantly reducing forage quality. Our objectives were to determine if including a perennial grass with alfalfa influenced forage quality, and alfalfa quality, maturity, and morphological characteristics at each of three annual harvests. For 2 yr at two locations, alfalfa, alfalfa‐smooth bromegrass (Bromus inermis Leyss.), and alfalfa‐timothy (Phleum pratense L.) were sampled three times annually at bud to one‐tenth bloom stage of alfalfa. Mean stage by weight, mean stage by count, stem length, and shoot weight of alfalfa were measured. Crude protein (CP), acid detergent fiber, and neutral detergent fiber (NDF) concentrations were determined for each forage and for alfalfa. Seeding bromegrass or timothy with alfalfa reduced CP on average 13% and increased NDF on average 12% at the first spring harvest, but not in subsequent harvests. Forage quality was higher for alfalfa grown with grass than for alfalfa grown alone at second harvest. Alfalfa component yield reduction in the mixtures was not directly proportional to grass yield. As a result, mixtures yielded more than alfalfa alone at the first harvest but less at the second harvest. Grass influenced alfalfa maturity, stem length, and shoot weight primarily at second harvest.
Mapping Gene(s) for Grain Protein in Tetraploid Wheat (Triticum turgidum L.) Using a Population of Recombinant Inbred Chromosome Lines
Authors: Joppa L. R. , Du Changheng , Hart Gary E. , Hareland Gary A.
Published: July 2010

A ‘Langdon’ durum wheat line with a pair of 6B chromosomes from an accession of Triticum turgidum L. var. dicoccoides (Körn. in litt., in Schweinf.) Bowden [LDN(DIC‐6B)] previously was shown to have a gene(s) for high grain protein content (GPC). The objectives of this study were to develop a mapping population segregating only for genes on chromosome 6B, map the gene(s) for high GPC, and identify closely linked markers for use in marker‐assisted breeding for this trait. The 6B mapping population was grown in replicated field trials and evaluated for GPC. A restriction fragment length polymorphism (RFLP) map of this population was available. The quantitative trait locus (QTL) analyses provided strong evidence that a gene(s) for high GPC (named QGpc.ndsu‐6Bb) is located near the centromere of 6B. The most likely location for the gene(s) is in the short arm between Xabg387‐6B and Xmwg79‐6B. The logarithm of the odds (LOD) score for this interval is 18.9. Segregation in this segment accounted for 66% of the variation in GPC. Eleven additional markers have been mapped within 7 centimorgans (cM) of the midpoint of Xabg387‐6B and Xmwg79‐6B. One or more of these markers should be useful in marker‐assisted breeding for high GPC in dorum wheat.
Development of a DNA Marker for Fusarium Wilt Resistance in Chickpea
Authors: Mayer M. S. , Tullu Abebe , Simon C. J. , Kumar J. , Kaiser W. J. , Kraft J. M. , Muehlbauer F. J.
Published: July 2010

Fusarium wilt caused by Fusarium oxysporum Schlechtend.:Fr. f. sp. ciceris (Padwick) Matuo & K. Sato is the most widely spread soilborne disease of chickpea (Cicer arietinum L.). To advance our understanding of the genetics of wilt resistance and aid chickpea breeding programs, we developed a set of F6 recombinant inbred lines (RILs) between Fusarium wilt susceptible (C‐104) and resistant 315) parents. Prior screening of selected F3 plants identified two primers (UBC‐170 and CS‐27) that produced random amplified polymorphic DNA {RAPD) markers associated with Fusarium wilt race 1 resistance. Analysis of the RILs with these primers yielded an estimate of 7% recombination between the two markers and the locus for wilt resistance, and 6% recombination between the loci corresponding to the two RAPD markers. The DNA fragments were cloned and sequenced in order to construct primers that would amplify only the markers of interest. Primer pair CS‐27F/CS‐27R amplified a fragment linked to the allele for susceptibility to race 1 of Fusarium wilt and thus constitute allele specific associated primers (ASAPs), whereas UBC‐170FFLIBC‐170R produced a single band for both resistant and susceptible genotypes, thus demonstrating locus specificity rather than allele specificity. The use of markers generated by the RAPD or ASAP approaches can facilitate the introgression of resistance genes into susceptible lines and expedite the screening of chickpea germplasm resources and will be useful in extending the genetic map of chickpea.
A Sequential Clustering Strategy for Classifying Gene Bank Accessions
Authors: Franco Jorge , Crossa José , Díaz Jaime , Taba Suketoshi , Villaseñor José , Eberhart Steve A.
Published: July 2010

Statistical classification methods such as Normix, applied to groups previously formed (a priori groups) using hierarchical methods, can improve the a priori groups and give estimation of probabilities for membership. In this study, we used data from the evaluation of 29 maize (Zea mays L.) races to (i) apply Normix to the a priori groups formed by the Ward method (Normix after Ward), (ii) use the upper tail approach and a likelihood ratio test to estimate the optimal number of groups, and (iii) use three geometrical and statistical criteri (Mahalanobis distances, multivariate statistics, and trace and determinant of the within‐ and among‐group variability matrices) to compare the groups obtained from Ward per se and the Normix after Ward method. Results indicated that the reclassification of accessions by Normix substantially improved the a priori groups obtained by Ward in four ways: (i) the average Mahalanobis distance between groups was larger among Normix than among Ward groups; (ii) the ratio variability between groups to variability within groups is increased after Normix compared with that obtained after Ward; (iii) the generalized variance within groups is decreased in Normix compared with Ward; and (iv) the correlation coefficients between variables are increased after Normix compared with those correlation values obtained by Ward. Results suggested that the groups formed by the Normix after Ward procedure allows (i) good estimation of the optimal group number, (ii) formation of more compact and separated groups than the a priori groups formed by Ward per se, and (iii) estimation of the probability of accession membership to the groups.
Dosage Dependent Genetic Suppression of Oat Crown Rust Resistance Gene Pc‐62
Authors: Wilson W. A. , McMullen M. S.
Published: July 2010

Combining crown rust resistance (CRR) genes is an objective many oat (Avena sativa L.) breeding programs. Genetic suppressors of CRR have been reported, but the genetic nature of such suppressors has not been investigated. An excess of susceptible seedlings in segregating progeny of crosses involving genotypes with Pc‐38 and Pc‐62 suggested the Pc‐38 parent may have a factor that inhibits the expression of Pc‐62. Our objectives were to (i) examine a putative genetic interaction between oat CRR gene Pc‐62 and a dominant suppressor, (ii) utilize chromosomine terchanges tocks to define genetically the location of the suppressor, (iii) evaluate the effect of gene dosage combinations on the resistance‐suppression relationship, and (iv) examine alternative explanations of distorted segregation (genetic background and differential gametet ransmission). The use of duplication‐deficiency (Dp‐Df) genotypes placed a putative suppressor an interchanged chromosome segment that contains Pc‐38. Resistance conferred by Pc‐62 was suppressed in F1 trisomic CRR locus combinations (1 Pc‐62:2 Pc‐38) in comparison to the expression of resistance in F1 seedlings hemizygous for Pc‐62. The Pc‐38 segment contributed by two independently derived cultivars produced equivalent suppression in F1 combinations with Pc‐62. The presence of Pc‐38 in an interchanged position in the cultivar Dumont allowed production of mono‐ and diallelic combinations of resistance genes and evaluation of mono‐, di‐, and trisomic segregation of the CRR locus. Diallelic trisomic segregation for the CRR locus indicated that an increasing dosage of Pc‐62, relative to the suppressor and Pc‐38, decreased the degree of suppression. Male transmission of Dp‐Df gametes was not reduced relative to the frequency of gametes with a complete chromosome complement.