Intensifying intrinsic genetic variation in soybean [Glycine max (L.) Merr.] inbred lines
Susana A. Goggi
The soybean [Glycine max (L.) Merr.] is an economically important legume crop in the world. It is a source of nutritional vegetable oil and protein that is used for food, feed, and industrial purposes. The United States is the world's leading soybean producer with 32% followed by Brazil with 29%. Despite its economic importance, the genetic base of soybean cultivars has been reported to be narrow thus limiting crop improvement. Even though there is an apparent lack of genetic variation, soybean yields have continuously increased. Inbreeding plant species have shown intrinsic genetic variation; and the sources for this variability have been attributed to seed source, residual heterozygosity, and genetic mechanisms driven by the de novo genetic variation. In order to exploit intracultivar variation in established soybean lines, our studies were conducted with the intent of exploring various factors that may be contributing to this genetic variation. The objectives were to evaluate the effect of ultra-low plant densities, the accelerated aging test, simulated-hail, and sexual hybridization as seed- and plant-stress techniques. Single plants from inbred lines were maintained and evaluated during this study. During the growing season, single plants and their progeny were evaluated on the basis of flower color, pubescence color, and phenotypic variation within plots. Further evaluation through laboratory analysis included the examination of segregation patterns for aconitase-2 and aconitase-4 isozymes as well as segregation for DNA-based molecular markers. Phenotypic and genetic variation was observed within cultivars. During field evaluations, several mutants were observed which included lethal-yellow, viable-yellow, semi-sterile, and late maturity phenotypes. A large frequency of unexpected variation was detected in the progeny of plants grown in an ultra-low planting design and treated with an accelerated aging test. Although there is not a single factor contributing to this genetic variation, it is likely that plants grown in ultra-low densities might have an effect resulting in the generation of new genetic variants.