Distribution of virulent soybean aphid (Aphis glycines) biotypes in WI

A component of soybean aphid management strategies, host plant resistance, has undergone significant development in the past decade, and several resistance genes have been identified. However, soybean aphids that are virulent to resistant soybeans have also been discovered, revealing a need for virulence management strategies if the full potential of host plant resistance is to be realized. A critical component of any virulence management strategy is knowledge of the distribution and prevalence of virulent soybean aphids. Since discovery of soybean aphid “biotype 2” (virulent to Rag1) in Ohio, 2005 and “biotype 3” (virulent to Rag2) in Indiana, 2007, little has been discovered about the distribution of their lineages. In this study, soybean aphids were collected from several Wisconsin soybean fields during the summer of 2012, and performance was compared on Rag1 and Rag2 soybean lines with that of biotypes 1 (avirulent), 2 and 3. In addition, genotypes at 12 microsatellite loci were compared to give an estimate of genetic relatedness among WI-collected aphids and biotypes, and to test for unrestricted gene-flow among WI soybean aphids. The majority of WI-collected soybean aphids were avirulent to Rag1 and Rag2; however, one aphid isolate exhibited virulence to both Rag1 and Rag2. Genetic analyses revealed that WI soybean aphids were more differentiated from the biotypes than from each other, and that there is unrestricted gene-flow among WI populations. These results affirm the importance of  incorporating new resistance traits within commercial soybean lines.