Yield Response of Tolerant and Susceptible Soybean to the Soybean Aphid

Core Ideas Soybean aphid‐tolerance in KS4202 soybean is plant age dependent. Soybean aphid infestation occurring at the V1 stage impacts both susceptible and tolerant soybean. KS4202 during late vegetative and early reproductive stage tolerated high aphid pressure. Soybean aphid, Aphis glycines (Hemiptera: Aphididae), is the most economically important soybean [Glycine max (L.) Merr.] pest of North America. Multiple studies have identified soybean expressing antibiosis and/or antixenosis; however, soybean tolerance remains underexplored. Tolerance to soybean aphid injury was previously identified in soybean KS4202. This research examined the yield response of KS4202 infested with soybean aphid at specific plant stages and identified at what plant stage tolerance initiates. A preliminary study evaluated the yield parameters of the tolerant genotype at low (4000–5500 cumulative aphid‐days [CAD]) and high aphid pressure (7500–8500 CAD) at different growth stages (V1, V3, and R1). A second study compared the yield response of the tolerant and a susceptible genotype (K03‐4686) at both V1 and V3 stages. In addition, low and high aphid pressure increased to 9,000 to 12,000 and 18,000 to 25,000 for V1 and V3 stages, respectively. Preliminary evaluations indicated that the yield parameters of the tolerant genotype infested at V3 and R1 were not significantly different from the respective controls. Conversely, plants were unable to compensate for of high aphid pressure at the V1 stage. In study 2, high aphid pressure negatively influenced yield of both tolerant and susceptible V1‐plants infested, although the tolerant genotype compensated for low aphid pressure. Aphid pressures applied at the V3 stage did not influence the yield parameters of tolerant genotype; however, both aphid pressures were detrimental to the susceptible genotype. Tolerance in KS4202 begins as early as V3, and maintains as plants mature.