Inheritance of resistance to the Soybean aphid in Soybean PI 200538
The soybean aphid (Aphis glycines Matsumura) is a major soybean [Glycine max (L.) Merr.] insect pest. Soybean plant introduction (PI) 200538 has strong resistance to the aphid. The objectives of our research were to determine the inheritance of resistance and to map gene(s) controlling resistance in PI 200538. F2 populations developed from crosses between PI 200538 and three susceptible genotypes were tested for resistance and with DNA markers. F2 plants from the cross ‘Ina’ x PI 200538 segregated 114 resistant to 37 susceptible and F2 plants from the cross ‘Williams 82’ x PI 200538 segregated 203 resistant to 65 susceptible when tested for resistance to soybean aphid biotype 1. F2 plants from the cross LD02-4485 x PI 200538 segregated 167 resistant to 62 susceptible when tested for resistance to biotype 2. These populations fit a 3:1 genetic ratio (P = 0.89, 0.78, and 0.52, respectively) with resistance dominant over susceptibility. Segregation among F2:3 families from the crosses supported the dominant resistance gene hypothesis. The gene mapped to soybean linkage group F, flanked by the simple sequence repeat marker loci Satt510, Soyhsp176, Satt114, and Sct_033, located in the same region as the aphid resistance gene Rag2. Since the resistance gene in PI 200538 also gave resistance to soybean aphid biotypes 1 and 2, it is possible that the gene is Rag2 and not a new aphid resistance gene. Therefore, PI 200538 may be an additional source of Rag2.