The development and use of a molecular model for soybean maturity groups.

BACKGROUND: Achieving appropriate maturity in a target environment is essential to maximizing crop yield potential. In soybean [Glycine max (L.) Merr.], the time to maturity is largely dependent on developmental response to dark periods. Once the critical photoperiod is reached, flowering is initiated and reproductive development proceeds. Therefore, soybean adaptation has been attributed to genetic changes and natural or artificial selection to optimize plant development in specific, narrow latitudinal ranges. In North America, these regions have been classified into twelve maturity groups (MG), with lower MG being shorter season than higher MG. Growing soybean lines not adapted to a particular environment typically results in poor growth and significant yield reductions. The objective of this study was to develop a molecular model for soybean maturity based on the alleles underlying the major maturity loci: E1, E2, and E3. RESULTS: We determined the allelic variation and diversity of the E maturity genes in a large collection of soybean landraces, North American ancestors, Chinese cultivars, North American cultivars or expired Plant Variety Protection lines, and private-company lines. The E gene status of accessions in the USDA Soybean Germplasm Collection with SoySNP50K Beadchip data was also predicted. We determined the E allelic combinations needed to adapt soybean to different MGs in the United States (US) and discovered a strong signal of selection for E genotypes released in North America, particularly the US and Canada. CONCLUSIONS: The E gene maturity model proposed will enable plant breeders to more effectively transfer traits into different MGs and increase the overall efficiency of soybean breeding in the US and Canada. The powerful yet simple selection strategy for increasing soybean breeding efficiency can be used alone or to directly enhance genomic prediction/selection schemes. The results also revealed previously unrecognized aspects of artificial selection in soybean imposed by soybean breeders based on geography that highlights the need for plant breeding that is optimized for specific environments.

Soybean seed lipoxygenase genes: molecular characterization and development of molecular marker assays.

Soybean seeds contain three lipoxygenase (Lox) enzymes that are controlled by separate genes, Lox1, Lox2 and Lox3. Lipoxygenases play a role in the development of unpleasant flavors in foods containing soybean by oxidation of polyunsaturated fatty acids. Null alleles for all three enzymes have been identified, lox1, lox2 and lox3, and are known to be inherited as simple recessive alleles. Previous studies determined that a missense mutation rendered Lox2 inactive; however, the genetic cause of either lox1 or lox3 mutation was not known. The objectives of this study were the molecular characterization of both lox1 and lox3 mutant alleles and the development of molecular markers to accelerate breeding for Lox-free soybean varieties. We identified two independent mutant alleles as the genetic causes of the lack of Lox1 in seeds of two lox1 mutant soybean lines. Similarly, a mutant allele that truncates Lox3 in a lox3 mutant soybean line was identified. Molecular markers were designed and confirmed to distinguish mutant, wild type, and heterozygous individuals for Lox1, Lox2 and Lox3 genes. Genotype and Lox phenotype analysis showed a perfect association between the inheritance of homozygous lox mutant alleles and the lack of Lox activity. Molecular characterization of a seed-lipoxygenase-free soybean line led to the discovery that an induced recombination event within the Lox1 gene was responsible for breaking the tight linkage in repulsion phase between mutant alleles at the Lox1 and Lox2 loci. The molecular resources developed in this work should accelerate the inclusion of the lipoxygenase-free trait in soybean varieties.