Impact of potassium deficiency on reproduction and growth of soybean aphid (Aphis glycines) on aphid-resistant soybean (Glycine max) lines

In conventional soybean (Glycine max), potassium (K) deficiency is associated with faster time to reproduction and greater nymph production in Aphis glycines (soybean aphid, SBA). Soybean lines with SBA resistance genes are nearing widespread commercialization; it is not known if resistance is maintained under K deficiency. Ten replicates of four soybean lines were planted in predator-proof cages in a K-deficient field in Montcalm County, Michigan. Two MSU lines carrying new Sparta genetics, E06902 (rag1b/ rag3 SBA resistant) and E07906-2 (rag1c/rag4 SBA resistant), were used along with LD16060 (Rag1 SBA resistant), and SD01-76R (SBA susceptible). Five cages were unfertilized, while five were amended with potash. Plants were infested with equal numbers of soybean aphids and populations were monitored weekly through the course of the growing season. No significant difference between aphid population numbers on plants in amended cages when compared to unfertilized cages even though significantly different plant K levels were detected. Aphid population numbers in cages exceeded the established 250 aphids/plant threshold, possibly explained by the discovery of a new aphid biotype.