Soybean [Glycine max (L.) Merr.] is one of the most important sources of plant‐based oil worldwide. Linolenic acid is associated with undesirable flavors and poor stability in soybean oil. Partial hydrogenation is typically used to reduce the levels of linolenic acid in soybean oil; however, this process results in the production of trans fatty acids. Studies have shown a link between increased risk of coronary heart disease and trans fatty acids present in hydrogenated oils. Thus, it is crucial to seek out genetic strategies to develop soybean lines with lower linolenic acid. To identify novel and useful alleles that could help reduce levels of linolenic acid in soybean, we screened a chemically mutagenized population. Three lines with reduced levels of linolenic acid in seed were identified. Mutant lines contained 3.8 to 4.5% of the total fatty acids as linolenic acid and carried independent mutations in the FAD3A gene encoding a desaturase responsible for the conversion of linoleic acid to linolenic acid in soybean seeds. To track the mutant alleles in a segregating population, allele specific markers were developed and the genetic association was confirmed with the reduced level of linolenic acid. These soybean lines will serve as a source of reduced linolenic acid to meet the breeding objectives of providing improved soybean lines.
Producers in the southern Great Plains usually dedicate fields of winter wheat (Triticum aestivum L.) to a grain‐only (GO) management system or one that incorporates grazing preceding grain harvest (dual‐purpose or DP system). We hypothesized that a grazing system may be applied as a selection tool during the early inbreeding generations to shift gene frequencies in favor of improved grazing tolerance and grain yielding ability. Grain yield and other key traits were compared among F5 bulk progenies of 24 populations exposed in the F2 to F4 generations to either system, including a Base set of F3 progenies and three cultivars. From GO and DP experiments conducted for 3 yr near Marshall, OK, the grain yield loss from GO to DP systems was 11% for ‘2174’ and ‘Custer’ and 24% for ‘Jagger’. Yields of DP selections exceeded the GO selections when tested in the DP system (220 kg ha−1 differential, P < 0.01) and in the GO system (80 kg ha−1, P = 0.01), with neutral effects on grain volume weight and protein concentration. Vegetative growth habit of DP and GO selections were visibly differentiated. When targeting a DP management system, derivation of bulk populations for line selection should utilize the DP system as a selection environment during the early inbreeding generations. This approach should not carry a universal yield penalty for GO environments when the breeding target includes both DP and GO systems.
To identify novel sources of genetic variation for the high oleic acid seed trait, soybean [Glycine max (L.) Merr] lines containing a higher fraction of oleic acid were identified through a forward‐genetic screen of a chemically mutagenized population. Mutant lines contained 30 to 40% of the total fatty acids as oleic acid. Nine of the lines identified contained novel point mutations in the FAD2–1A gene, which is known to be required for the conversion of oleic acid to linoleic acid. Mutation‐specific markers were developed to follow the mutant alleles in segregating populations and confirmed the genetic association of the novel polymorphisms with the elevated oleic acid trait. These lines can be used in breeding approaches and in combination with other genes to generate new soybean germplasm with high levels of oleic acid for the edible oil market.
This study is the first assessment of the entire soybean [Glycine max (L.) Merr] collection of the United State Department of Agriculture National Plant Germplasm System (USDA) reporting quantitative and population genomic parameters. It also provides a new insight into soybean germplasm structure. Germplasm studies enable plant breeders to incorporate novel genetic resources into breeding pipelines to improve valuable agronomic traits. We conducted comprehensive analyses on the 19,652 soybean accessions in the USDA-ARS germplasm collection, genotyped with the SoySNP50 K iSelect BeadChip SNP array, to elucidate the quantitative properties of existing subpopulations inferred through hierarchical clustering performed with Ward's D agglomeration method and Nei's standard genetic distance. We found the effective population size to be approximately 106 individuals based on the linkage disequilibrium of unlinked loci. The cladogram indicated the existence of eight major clusters. Each cluster displays particular properties with regard to major quantitative traits. Among those, cluster 3 represents the tropical and semi-tropical genetic material, cluster 5 displays large seeds and may represent food-grade germplasm, and cluster 7 represents the undomesticated material in the germplasm collection. The average FST among clusters was 0.22 and a total of 914 SNPs were exclusive to specific clusters. Our classification and characterization of the germplasm collection into major clusters provides valuable information about the genetic resources available to soybean breeders and researchers.
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