Exploring factors that may promote the longevity of Rag genes

Monday, June 1, 2015: 9:51 AM
McDowell + Tuttle (Manhattan Conference Center)
Adam Varenhorst , Entomology, Iowa State University, Ames, IA
Despite the genetic bottleneck that Aphis glycines passed through on the way to North America and the sparse use of aphid-resistant soybeans (i.e., Rag genes) in North America, biotypes have been identified that overcome this resistance. These biotypes are defined by their capacity to survive on aphid-resistant cultivars of soybean (e.g., biotype-2 survives on Rag1 soybean). However, there is limited evidence of fitness costs associated with these virulent biotypes. We conducted a series of experiments to determine if there are fitness costs associated with virulent biotypes on susceptible soybean. We evaluated biotype-2, biotype-3, and biotype-4 on susceptible soybean. Our results indicate that fitness costs exist for biotype-2, biotype-3, and biotype-4 on aphid-susceptible soybean. In addition, we also observed negative cross-resistance for biotype-2 on Rag2, and biotype-3 on Rag1 soybean. These results are the first to document fitness costs for biotype-2 and biotype-4 on susceptible soybean, and also the first to document negative cross-resistance of virulent biotypes toward Rag genes that they are not virulent towards.