Soybean Aphid Populations on Aphid Resistant and Susceptible Soybean Lines Growing under Potassium Deficiency

Abstract

The soybean aphid is an important pest of soybean in North America. A positive link between soybean aphid population growth and potassium (K) deficiency, perhaps related to a higher free amino acid concentration in deficient plants, is generally accepted. At least one aphid resistance trait, Rag1, has a lower concentration of several free amino acids, and thus reduced nutritional quality. Since K appears to influence nutritional quality as well, the objective of this study was to determine if antibiosis resistance of two soybean aphid resistance traits was maintained under K deficiency. Over three seasons, aphid populations on resistant (LD05‐16060, Rag1; E06902, rag1b/rag3) and susceptible (SD01‐76R) lines were compared in field cages under K‐deficient and sufficient conditions. When lines were caged separately, the number of soybean aphids per plant on the susceptible line was significantly greater on deficient compared to fertilized plants. However, the Rag1 and rag1b/rag3 traits maintained resistance under the same conditions. When lines were caged together, and winged aphids from the susceptible line continuously deposited nymphs on the resistant lines, aphid populations on the resistant lines still remained far below the population on the susceptible line, and below the economic injury level of 674 soybean aphids per plant, under both K‐fertilized and K‐deficient conditions. Thus, resistance to soybean aphid was maintained in two soybean lines with different resistance genes, even when K was deficient.