Is pyramiding resistance the answer for soybean aphid management?

The soybean aphid is the leading insect threat to soybean production in the Midwestern United States.  Host plant resistant varieties have been released for soybean aphid control.  These varieties contain the Rag1 gene conferring antibiosis resistance to the soybean aphid.  In other systems aphids have rapidly developed virulence to single gene resistance traits.  We conducted a regional small plot field experiment with sixteen locations across eight states and two years.  We evaluated near-isolines of soybean for the ability of single gene resistant lines containing the Rag1 and Rag2 genes and a pyramid line containing both genes to limit plant exposure to aphids (CAD) and protect yield as compared with a susceptible line. We used a split-plot design with soybean line as the whole-plot effect and aphid exposure, “aphid-free” or “untreated”, as the sub-plot effect.  Aphid-free sub-plots were kept at densities of >50 aphids plant^-1 with foliar applications of insecticide.  For the purpose of this presentation, data will be presented from three locations, which experienced economically damaging populations of soybean aphids. All three soybean aphid-resistant lines significantly decreased CAD at all locations.  The pyramid line accumulated significantly fewer CAD than both single gene lines at two of three locations. Yield was significantly reduced in the untreated split-plot for the susceptible line and numerically reduced for both single gene lines.  We were unable to measure a yield decrease, significant or numerical, for the pyramid line.  These results demonstrate that pyramiding resistance genes provides sufficient and consistent yield protection for soybean aphid management.