Phenotypic variation for saturated fatty acid content in soybean

Summary Concern over high saturates in human diets has prompted the development of soybean [Glycine max (L.) Merr.] lines producing oil with reduced saturated fatty acid concentration. To better understand those factors that influence phenotypic expression for palmitic and stearic acid content in soybean, thirty soybean lines random for saturated fatty acid content were grown in eight field environments contrasting for mean temperature during seed-filling. Palmitic and stearic acid content varied significantly (P<0.01) both among genotypes and across environments, while genotype x environment interactions were reflected in changes in line variance and ranking for both traits. Therefore selection of a superior genotype for saturated fatty acid composition may not correlate well from one environment to another. In general, early-maturing lines were less sensitive than later-maturing lines in their response to changes in mean daily temperature for palmitic concentration. However, factors in addition to temperature appeared to influence genotype response for stearic acid content. It appears that genetic systems conditioning palmitic and stearic acids are independent, and that separate breeding strategies need be adopted to make simultaneous improvement for these two oil traits. In summary, development of soybean lines with low or high saturated fatty acid content may be accomplished through evaluation and selection in a few environments contrasting for temperature.Cooperative investigations of the USDA-ARS, and North Carolina Agric. Res. Serv., Raleigh, NC, U.S.A.     

Association of isozyme genotypes with agronomic and seed composition traits in soybean

Summary Two crosses between Glycine max (L.) Merr. and G. soja Sieb. & Zucc. parents were used to study the association between isozyme marker loci and agronomic and seed composition traits in soybean. The parents possessed different alleles at six isozyme loci for Cross 1 (A80-244036 × PI 326581) and at eight isozyme loci for Cross 2 (A81-157007 × PI 342618A). A total of 480 BC₂F_4:6 lines from the two crosses was evaluated for 13 traits in two environments. Lines were grouped in locus classes from 0 to 5 according to the number of loci homozygous for the G. soja alleles that they possessed. Within each locus class, each isozyme genotype was represented by five random lines.Selection for G. max alleles at the isozyme loci was not effective in recovering the recurrent parent phenotype in either cross. In cross 1, however, BC₂F₄-derived lines in the 0- or 1- locus class more closely resembled the G. max parent than lines in the 4- or 5- locus classes for most of the agronomic and seed composition traits evaluated. Significant associations were found between particular isozyme genotypes and every trait analyzed. The estimated effect of genes linked to the Pgm1 locus was a delay in maturity of 6.0±3.4 days. In cross 1, the Idh2 locus was associated with a significant effect on linolenic acid content. The percentage of variation accounted for by the models of estimation varied according to the heritability of the trait. The R² was high (up to 78%) for maturity, lodging, and vining, and low (up to 21%) for seed yield. Most of the variation was associated with the BC₂F₁ family from which the lines were derived. There was little evidence that digenic epistasis was an important source of variation.Journal Paper No. J-13505 of the Iowa Agric. Home Econ. Exp. Stn., Ames, IA, Project 2475.     

Association analysis using SSR markers to find QTL for seed protein content in soybean

Association analysis studies can be used to test for associations between molecular markers and quantitative trait loci (QTL). In this study, a genome-wide scan was performed using 150 simple sequence repeat (SSR) markers to identify QTL associated with seed protein content in soybean. The initial mapping population consisted of two subpopulations of 48 germplasm accessions each, with high or low protein levels based on data from the USDA’s Germplasm Resources Information Network website. Intrachromosomal LD extended up to 50 cM with r ² > 0.1 and 10 cM with r ² > 0.2 across the accessions. An association map consisting of 150 markers was constructed on the basis of differences in allele frequency distributions between the two subpopulations. Eleven putative QTL were identified on the basis of highly significant markers. Nine of these are in regions where protein QTL have been mapped, but the genomic regions containing Satt431 on LG J and Satt551 on LG M have not been reported in previous linkage mapping studies. Furthermore, these new putative protein QTL do not map near any QTL known to affect maturity. Since biased population structure was known to exist in the original association analysis population, association analyses were also conducted on two similar but independent confirmation populations. Satt431 and Satt551 were also significant in those analyses. These results suggest that our association analysis approach could be a useful alternative to linkage mapping for the identification of unreported regions of the soybean genome containing putative QTL.     

Tagging the juvenile locus in soybean [Glycine max (L.) Merr.] with molecular markers

Soybean cultivars carrying the `long juvenile trait' show a delayed flowering response under short day conditions. The incorporation of this character into genotypes of agronomic interest may allow a broader range of sowing dates and latitudes for a single cultivar adaptation. The objective of this work was to identify molecular markers linked to the juvenile locus in soybean. Experiments were carried out using two pairs of near isogenic lines(NILs) differing in the presence of the long juvenile trait, and RAPD markers. Four hundred primers were first screened to find polymorphism associated with the trait. Additional differences between NILs were sought by digesting the genomic DNA with five restriction enzymes. Polymorphic fragments detected between NILs were tested for linkage to the juvenile locus in the corresponding F₂ segregating populations. Marker bc357-HaeIII was linked (χ²L = 46.316) to the juvenile locus with an estimated recombination frequency of 0.13 ± 0.03in one of the genetic backgrounds studied. The fragment was cloned, sequenced and converted into a SCAR marker. Moreover,bc357-HaeIII was used as RFLP probe. Both, SCAR and RFLP generated markers linked to the juvenile locus in the two genetic backgrounds analysed. Results presented in this work can be utilised for both, the localisation of the gene associated with the character and for tagging the juvenile trait in soybean breeding programs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of resistance to pendimethalin herbicide induced stem damage in soybean

Selective herbicides are valuable weed control tools; however, selectivity is not always complete, resulting in crop damage. Stem breakage, lodging, and enlarged hypocotyls (brittle bean syndrome) limit yields of soybean [Glycine max (L.) Merr.] genotypes treated with pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine]. Developing genotypes with resistance to pendimethalin injury would eliminate or reduce this problem. Genetic studies were conducted to determine the inheritance of resistance to pendimethalin induced stem damage. The F_2:3 progeny of crosses involving resistant ('Asgrow A4715' and 'Flyer') and susceptible (`Essex' and K87-7-95) genotypes were screened in a greenhouse. Each genotype was treated with 1.68 kg ha^-1 pendimethalin preemergence and irrigated as needed. Plants were scored at V4 for stem breakage. Progeny distributions indicated that resistance to brittle bean syndrome damage behaved as a quantitative trait. Dominance for stem breakage was expressed in the population of A4715 × Essex. Flyer was more sensitive to herbicide damage than Asgrow A4715 because it has fewer genes for resistance or different alleles. The F_2:3 variance component heritability estimates ranged from 0.19 to 0.52. Gain from selection for resistance to pendimethalin injury is possible, and resistant progeny can be recovered from segregating populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance of resistance to Soybean mosaic virus in FT-10 soybean

The occurrence of a new isolate from the G5 strain of Soybean mosaic virus (SMV), which broke the resistance of soybean cultivar FT-10, was first reported in Brazil in 1995. Cultivar Davis is an ancestor of ‘FT-10’ and the likely source of resistance to the virus. Diallel crosses among resistant cultivars Epps (PI 96983), Ogden and FT-10, and susceptible cultivar Hill were made to investigate the inheritance of SMV resistance in FT-10. The experiments for genetic studies were performed undergreen house conditions. Plants of the F₂ population and F₃ families from each cross and the parents were inoculated with SMV G1 and G5 strains. Plants were classified as: symptom less (R), susceptible with typical symptoms of mosaic (S), and systemic necrosis (N). Plants showing necrosis or no symptoms were classified as resistant. Each F₃ family was classified as resistant (homozygous),susceptible (homozygous), or segregating (heterozygous). The results of both F₂ and F₃ were analyzed by Chi-square tests. The results suggested that FT-10 carries an allele at the Rsv ₁ locus for resistance to SMV. However, the allele is different from those in Epps and Ogden. The symbol Rsv ₁ ^d is a tentatively named for the newly detected allele in FT-10. This allele probably originated from Davis cultivar. This revised version was published online in July 2006 with corrections to the Cover Date.     

RAPD markers linked to resistance to downy mildew disease in soybean

To determine and utilize RAPD markers linked to resistance to downymildew incited by Peronospora manshurica in soybean, a resistantcultivar `AGS129' was crossed to a susceptible cultivar `Nakhon Sawan 1'(NS1). F₂ and BC₁ populations were advanced from the F₁ and evaluatedfor resistance to the disease. ²-test demonstrated that the resistancewas controlled by a single dominant gene (Rpmx). Near-isogenic lines(NILs) and bulked segregant analysis (BSA) were used to identify RAPDmarkers linked to the gene. Six DNA bulks namely F₅(R), F₅(S),BC₆F₃(R), BC₆F₃(S), F₂(R) and F₂(S) were set up by pooling equalamount of DNA from 8 randomly selected plants of each disease responsetype. A total of 180 random sequence decamer oligonucleotide primerswere used for RAPD analysis. Primer OPH-02 (5 TCGGACGTGA 3 andOPP-10 (5 TCCCGCCTAC 3) generated OPH-02₁₂₅₀ and OPP-10₈₃₁fragments in donor parent and resistant bulks, but not in the recurrentparent and susceptible ones. Co-segregation analysis using 102 segregatingF₂ progenies confirmed that both markers were linked to the Rpmxgene controlling downy mildew disease resistance with a genetic distance of4.9 cm and 23.1 cm, respectively. Marker OPH-02₁₂₅₀ was presentin 13 of 16 resistant soybean cultivars and absent in susceptible cultivars,thus confirming a potential for MAS outside the mapping population.     

A cluster analysis of wild and domesticated soybean phenotypes

Summary Cluster analysis techniques were used to examine phenotypic variation within the USDA Soybean Germplasm Collection. This study included ten Plant Introductions each of the domesticated soybean, Glycine max (L). Merr., the wild soybean, G. soja Sieb. & Zucc., and a disputed species, G. gracilis Skvortz. G. max and G. soja were found to be morphologically distinct entities and G. gracilis was found to be conspecific with G. max. Because G. gracilis probably represents weedy races associated with the cultivated soybean and because gracilis phenotypes can be distinguished from G. max, the designation, G. max forma gracilis, is recommended.Joint contribution: North Central Region, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Journal Paper No. J-9389 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011; Project 2107.     

Genetic variation in soybean (Glycine max (L.) Merril) for cookability and water absorption during cooking

Summary Improvement of cookability is an important objective in breeding of food legumes. The present study was undertaken to investigate variation in cookability in soybean. Genetic variation was observed among lines from two crosses. Absence of associations between cookability and protein content, oil content and grain yield indicate that selection for cookability can be achieved without adversely affecting the expression of these characters.     

DNA profiling and genetic diversity of Korean soybean (<Emphasis Type="Italic">Glycine max</Emphasis> (L.) Merrill) landraces by SSR markers

Approximately 7,000 accessions of Korean soybean (Glycine max (L.) Merrill) landraces, largely composed of three collections, the Korea Atomic Energy Research Institute’s soybean (KAS), the Korean Crop Experiment Station’s soybean (KLS) and the Korean Agricultural Development and Technology Center’s soybean (KADTC) collections, have been conserved at the Rural Development Administration (RDA) genebank in Korea. The accessions within collections were classified based on their traditional uses such as sauce soybean (SA), sprouted soybean (SP), soybean for cooking with rice (SCR), and OTHERS. A total of 2,758 accessions of Korean soybean landraces were used to profile and to evaluate genetic structure using six SSR loci. A total of 110 alleles were revealed by at the six SSR loci. The number of alleles per SSR locus ranged from 9 to 39 in Satt187 and Satt_074, respectively. The number of alleles ranged from 87 in the KADTC collection to 96 in the KLS collection, and from 63 in the SCR group to 95 in the SP group. Nei’s average genetic diversity ranged from 0.68 to 0.70 across three collections, and 0.64 to 0.69 across the usage groups. The average between-group differentiation (G _st) was 0.9 among collections, and 4.1 among the usage groups. The similar average diversity among three collections implies that the genetic background of the three collections was quite similar or that there were a large number of duplicate accessions in three collections. The selection from the four groups classified based upon usage may be a useful way to select accessions for developing a Korean soybean landrace core collection at the RDA genebank. DNA profile information of accessions will provide indications of redundancies or omissions and aid in managing the soybean collection held at the RDA genebank. The information on diversity analysis could help to enlarge the genetic diversity of materials in breeding programs and could be used to develop a core collection.     

Establishment of Chinese soybean Glycine max core collections with agronomic traits and SSR markers

It is very important to efficiently study and use genetic diversity resources in crop breeding and sustainable agriculture. In this study, different sampling methods and sample sizes were compared in order to optimize the strategies for building a rationally sized core collection of Chinese soybean (Glycine max). The diversity in the core collection captured more than 70% of that in the pre-core collection, no matter what sampling methods were used, at a sampling proportion of 1%. Core collections established with both simple sequence repeat (SSR) marker data and agronomic traits were more representative than those chosen on an independent basis. An optimal sampling method for a soybean core collection was determined, in which strategy ‘S’ (allocating accessions to clusters according to the proportion of square root of the original sample size within each ecotype) was used based on SSR and agronomic data. Curve estimation was used to estimate the allelic richness of the entire Chinese soybean germplasm and a minimum sample size for a core collection, on which a sampling proportion of about 2% was determined to be optimal for a core collection. Further analysis on the core collection with fourteen agronomic traits and allelic constitution at 60 SSR loci suggested that it highly represented the entire collections both on genetic structure and diversity distribution. This core collection would provide an effective platform in proper exploitation of soybean germplasm resources for the study of complex traits and discovering important novel traits for crop genetic development.     

Heterosis of interspecific soybean hybrids for traits related to N2 fixation

Summary Three greenhouse experiments were conducted to compare the performance of soybean (Glycine max (L.) Merr.), wild soybean (G. soja Sieb. et Zucc.), and soybean x wild soybean hybrids for traits relating to N₂ fixation including nodulation, acetylene reduction, nodule leghemoglobin concentration, and nitrogen (N) accumulation and dry matter (DM) accumulation. In all three experiments G. max generally exceeded G. soja in nodulation, acetylene reduction, and N and DM accumulation while the soybean possessed higher nodule leghemoglobin concentration. In Experiment I, the mean of the hybrids did not differ significantly from the G. max parent in nodule mass, acetylene reduction activity, nodule leghemoglobin concentration, or DM accumulation. The hybrids did exceed the soybean parent in N accumulation, thus demonstrating high parent heterosis. In Experiments IIA and IIB with a more carefully chosen set of G. soja parents, high parent heterosis of individual crosses was common. Across the three experiments average high parent heterosis was 34, 28, and 28%, respectively, for nodule mass, N accumulation, and DM accumulation. If one accepts the assumption that hybrid vigor results from the accumulation of dominant alleles, then these alleles could theoretically be accumulated via selection in a homozygous genotype. If this is true than the results of the experiments reported here suggest that interspecific soybean x wild soybean crosses could serve as sources of homozygous lines which would exceed currently available soybean cultivars in nodule mass, and N and DM accumulation.This work was supported in part by the USDA Competitive Grants Program, Grant 82-CRCR-1-1039 and Cooperative Agreement 58-32U4-2-370 between the U.S. Department of Agriculture and the Agronomy Department, University of Maryland, Scientific Article No. A-4648, Contribution No. 7644 of the Maryland Agricultural Experiment Station.     

Relationship between soybean pubescence density and soybean mosaic virus field spread

An important factor in the natural spread of soybean mosaic virus (SMV) is that viruliferous aphid landing must be followed by probing. Previous studies showed that increased pubescence density of soybean provided resistance to SMV by inhibiting the probing activities of aphids. In this study we compared the incidence level of SMV infection in six `Clark' isolines with different pubescence densities and fit the disease progress curves (increase with time in the percent of plants infected with SMV) in three Clark isolines with normal, dense, and extra-dense pubescence to compare patterns of SMV spread in the field. Our objectives were (1) to corroborate the effects of dense pubescence on the incidence level of SMV infection and extend this to soybean with extra-dense pubescence; (2) to characterize the effects of pubescence density on occurrence of SMV epidemics. Each increase in pubescence density reduced the incidence level of SMV infection. The pubescence density of soybean affected the disease progress curves of SMV. The dense pubescence isoline had a lower upper asymptote parameter, and the extra-dense pubescence isoline had both a lower upper asymptote parameter and a larger delay parameter than the normal pubescence isoline. On the other hand, denser pubescence did not significantly affect the rate of SMV spread. Therefore, dense pubescence provided resistance to SMV by reducing the maximum incidence of SMV infection while extra-dense pubescence provided resistance by both reducing the maximum incidence of infection and delaying the time at which maximum SMV spread occurred. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of resistance to soybean cyst nematode in PI 438489B

Soybean (Glycine max L. Merr.) plant introduction PI 438489B is a unique source that has resistance to all known populations of soybean cyst nematode (Heterodera glycines Ichinohe, SCN). This PI line also has many desirable agronomic characteristics, which makes it an attractive source of SCN resistance for use in a soybean breeding program. However, characterization of SCN resistance genes in this PI line have not been fully researched. In this study, we investigated the inheritance of resistance to populations of SCN races 1, 2, 3, 5, and 14 in PI 438489B. PI 438489B was crossed to the susceptible cultivar ‘Hamilton’ to generate F₁ hybrids. The random F₂ plants and F₃ lines were evaluated in the greenhouse for reaction to these five populations of SCN races. Resistance to SCN races 1, 3, and 5 were mostly conditioned by three genes (Rhg Rhg rhg). Resistance to race 2 was controlled by four genes (Rhg rhg rgh rgh). Three recessive genes were most likely involved in giving resistance to race 14. We further concluded that resistance to different populations of SCN races may share some common genes or pleiotropic effects may be involved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of isoflavone contents in soybean seeds

Summary We studied the genetic basis of isoflavone content inheritance in soybean seeds. The progenitors BARC-8 (low isoflavone content), IAC-100 (high isoflavone content), the F₁ and F₂ populations derived from reciprocal crosses, and backcross populations were analyzed for isoflavone content and composition. Six isoflavones were detected: daidzin (DZ), genistin (GT), glycitin (GC), malonyldaidzin (MDZ), malonylgenistin (MGT) and malonylglycitin (MGC). DZ, GT, MDZ and MGT contents were influenced by the cytoplasm and the nuclear genes of the maternal parent. For this reason, a genetic model was considered that included the cytoplasmic effect and epistasis between nuclear and cytoplasmic genes. Except for GT, the additive effect was the most important one. For GT content the cytoplasmic effect was the most important. Except for MDZ, the epistatic effects were significant for all the isoflavone forms. Our data indicate that genetic improvement for these traits should explore the additive genetic variances in superior lines or the cytoplasmic effect and the epistatic interactions between cytoplasmic and nuclear genes to obtain the largest selection gains.     

Multivariate analysis of a collection of soybean cultivars for southwestern Spain

Summary Multivariate techniques were used to classify 125 soybean lines into clusters. Late maturing varieties belonging to maturity group III showed the best adaptation to the ecological conditions of the area when soybeans were sown at early planting dates. A group of experimental lines, the majority of which had semideterminate stem termination with small leaflets and intermediate maturity, were highly productive when grown as a second crop. Some lines of other groups were identified as likely parents for use in a breeding program to improve agronomic characteristics. The identified groups were quite stable in their performance through changes in environmental conditions (years and planting dates). The analyses indicated that some intercorrelated traits can be omitted in future line evaluation.Experimental work and data analyses supported by the Instituto Nacional de Investigaciones Agrarias of Spain and the IRI Research Institute, Inc. through a World Bank Grant.INIA, Moncada (Valencia), Spain INIA, Madrid, Spain; and Iowa State University, Ames, Iowa 50011. Consultant with IRI Research Institute, Inc. (1975–77).     

Agronomic characteristics and genetics of a chromosome interchange in soybean

Summary A chromosome interchange in soybean (Glycine max (L.) Merr.) was studied agronomically and genetically, and comparisons of seed or abortion position within the pod were related to chromosome structure. Comparisons were among plants heterozygous for a chromosome interchange (N/T), plants homozygous for the interchange (T/T), and homozygous normal-chromosome plants (N/N). The latter two genotypes were male fertile and female fertile. Heterozygous interchange plants, which are about 50% pollen sterile and ovule sterile, are typical of a large number of plants that have equally frequent alternate and adjacent chromosome segregation. Yield, lodging, plant height, and seed oil and protein percentages among all three genotypes were similar even though significant differences existed for seed weight, seed number, and pod number per plant. Seed abortions were more frequent in the basal position of the pod than in either the middle or apical positions in N/N and T/T genotypes. Ovule abortions in N/T plants were equally frequent among all positions both in two- and three-ovule pods. The middle seed in a three-ovule pod was heavier than the basal or apical seed among all three genotypes.Joint contribution: USDA ARS, and Journal Paper No. J-11300 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011, USA, Project 2471.USDA ARS, Department of Agronomy and Genetics, Iowa State University, Ames, Iowa 50011, USA.Department of Agronomy, Iowa State University, Ames, Iowa 50001, USA.     

Genetic control of fatty acid composition in seed oil of Sinapis alba L.

Summary Inheritance of fatty acid composition was studied in an F1 diallel cross in Sinapis alba. Crosses were made among accessions having contrasting amounts of oleic (C18:1) and erucic (C22:1) acid. Concentrations of oleic, linoleic (C18:2), eicosenoic (C20:1) and erucic (C22:1) acids were determined by gas-chromatography for each mating combination. Genetic analysis confirmed that the composition of the fatty acids was controlled mainly by the nuclear genes of the embryo. Additive gene action with partial dominance for the reducing alleles was noted for oleic and linoleic acids, while erucic acid showed an additive mode of inheritance with partial dominance for the enhancing alleles. Positive heterosis was demonstrated for eicosenoic acid content. Erucic acid content was strongly negatively correlated with oleic acid, suggesting a genetic interdependence between the two fatty acids. Broad-sense and narrow-sense heritability estimates for each of oleic, linoleic and erucic acids were very high, due to low between-plants non-genetic component of variance.Contribution No. 3662-E, 1992 series.     

Resistance to soybean cyst nematode and molecular polymorphism in various sources of Peking soybean

Summary Cultivar Peking has been extensively used as a source of resistance to Race 3 and Race 5 of soybean cyst nematode, Heterodera glycines I., and Peking genes for resistance are present in a wide range of resistant soybean cultivars. Peking is also used as a host differential in the soybean cyst nematode race classification system. Thirteen Peking lines maintained in the USDA Soybean Germplasm Collection and in several breeding programs were surveyed using RFLP and RAPD markers for genetic characterization. Based on the molecular diversity combined with reaction to soybean cyst nematode, Peking genotypes from a common original source were identified. Peking lines PI 297543 (introduction from Hungary), and PI 438496A, PI 438496B and PI 438496C (introductions from Russia) represented unrelated germplasms. Identified molecular polymorphism can be used to validate the genetic purity of Peking lines used as host differentials for soybean cyst nematode classification system as well as utilization of an individual germplasm line in genetic-breeding programs.