Characterization of Novel Low Phytate and Low Stachyose Germplasm for Soybean Breeding.

Plant breeding programs developing cultivars with improved seed composition need to understand the genetic and phenotypic effects associated with incorporating novel genes. The development of soybeans with reduced phytate and stachyose levels has nutritional and environmental benefits, but poor agronomic performance presents breeding challenges.  Our objectives were to characterize a unique gene conditioning the low phytate, low stachyose, and high sucrose traits in the Virginia Tech soybean experimental line V03-5901 to determine the genetic mechanism controlling the accumulation of phytate and stachyose, determine the phenotypic correlations for seed composition traits, and evaluate agronomic characteristics for effects associated with the integration of low phytate and stachyose germplasm.  In 2008, a F₂ soybean population developed from a cross between V01-1693 (normal phytate) and V03-5901 (low phytate) was evaluated in Blacksburg, Virginia.  The germination percentages were low, only 42% of F₂ seeds germinated compared to 66% and 67% for the parents V03-5901 and V01-1693, respectively.  Ground subsamples of F_2:3 seeds were analyzed for inorganic phosphorous (Pi), sucrose, raffinose and stachyose levels and transgressive segregants were identified for all traits.  Sixteen F_2:3 individuals were classified as low phytate based on the inverse relationship between Pi and phytate.  Among all F_2:3 lines the phenotypic correlations were highly significant (P < 0.01) between the following seed components: Pi, sucrose, raffinose and stachyose.  Pi concentrations were negatively correlated with raffinose and stachyose, which is beneficial for developing soybeans with improved seed composition.  F_2:3 seeds were planted in Costa Rica for seed increase and germination rates of low phytate lines averaged 88.9% compared to 89.3% for the whole population.  During the 2009 planting season, F_2:4 lines will be evaluated in replicated yield trials to explore agronomic characteristics associated with seed composition traits.