Is pyramiding resistance the answer for soybean aphid management?

The soybean aphid (Aphis glycines Matasumura) is a threat to soybean production in the Midwestern United States. Varieties containing the Rag1 soybean aphid resistance gene have been released with limited success in reducing aphid populations. Furthermore, virulent biotypes have been discovered within North America, challenging the durability of single-gene resistance. Pyramiding resistance genes has the potential to increase aphid population suppression and increase resistance gene durability. Our goal was to determine if a pyramid could provide increased aphid population suppression across a wide range of environments. We conducted a small-plot field experiment across seven states and three years. We compared soybean near-isolines with the Rag1 or Rag2 gene, a pyramid line containing both genes to limit plant exposure to aphids and protect yield as compared with a susceptible line.  Compared to the susceptible line, all aphid-resistant lines significantly decreased plant exposure to aphids at all locations but one. The pyramid line experienced lower exposure to aphids than both single gene lines at eight of 21 location-years. Soybean aphids significantly reduced soybean yield for the susceptible line and for both single gene lines, however we did not observe a significant or numerical yield decrease due to soybean aphids on the pyramid line. These results demonstrate that pyramiding resistance genes can provide sufficient and consistent yield protection from soybean aphid in North America.