Evaluating Progeny of Glycine Max by Glycine Tomentella for Novel Disease Resistance.

Hybridization with wild relatives of crops is an important tool for improving traits such as disease resistance and our objective is to expand the use of wild relatives for disease resistance in soybean.  Glycine tomentella (2n=78) is a wild, perennial species in the tertiary gene pool of soybean (G. max, 2n=40).  G. tomentella has been shown to have high levels of resistance to several diseases, including soybean rust and soybean cyst nematode.  Through culturing immature hybrid seeds and doubling the chromosome number with colchicine, we developed partially fertile amphidiploid plants with 2n=118. After two to five backcrosses to the cultivar Dwight, we obtained 2n=40 and 2n=42 genetically stable lines.  There is no obvious chromosome pairing in the initial F1 hybrid between G. max and G. tomentella and phenotypic evaluation of the derived fertile progeny confirms minimal introgression of G. tomentella genes.  From our 2n=40 lines, we identified lines with resistance to multiple races of Phytophthora sojae and research is underway to fully characterize the genetic relationship to known Rps genes in G. max.  Using greenhouse screening, we also identified partial resistance to Fusarium virguliforme, the causal agent of sudden death syndrome. For both of these diseases, the resistance in the derived lines is significantly better than that in Dwight. Transferring useful disease resistance from Glycine tomentella to soybean is a major challenge. By developing genetic tools to assist in the process and creating a larger pool of derived lines to evaluate, we are making significant progress in achieving this goal.