Inheritance and characterization of soybean aphid resistance in soybean germplasm accession PI71506

Soybean aphids (Aphis glycines Matsumura) continually establish populations of economic importance in soybean [Glycine max (L.) Merr.] production areas. Insecticide application costs and yield loss prompt the development of resistant varieties. The soybean germplasm accession PI71506 has been shown to convey antixenotic host plant resistance but is suspected to also possess genes for antibiosis. The objectives of this study were to determine the inheritance of resistance from PI71506, further characterize the resistance exhibited by PI71506, compare phenotypic and genotypic expression of resistance in Dowling and PI71506, and to begin finding associations between molecular markers and host plant resistance in PI71506. We crossed two adapted susceptible cultivars, SD1111RR and SD01-3219R with PI71506 to create F₂ populations and subsequent F_2:3 populations for resistance screening. Individual F₂ plants were screened in greenhouse tests utilizing small sticky cages. Pooled F₂ data in chi square tests revealed a goodness of fit of P=0.08 and P=0.64 for a single dominant gene segregation of 3:1 in both populations. We screened F_2:3 populations in aphid field cage trials during the 2008 growing season and found they fit a single dominant gene model (P=0.19). Comparisons with Rag 1 resistance in Dowling confirmed these findings in both generations of resistance testing. Although significant differences existed in the resistance level between parent lines and their respective populations, the distributions of populations derived from Dowling resistance were consistent with the distributions of PI71506. The aphid check varieties in both green house and field cage trials showed significant differences between resistance and susceptibility. In performance tests with the Ohio aphid biotype, PI71506 had a significantly different aphid population mean than susceptible checks SD1111RR and S-19R5. This shows that the resistance conveyed by PI71506 was effective against the Ohio isolate. SSR markers revealed that PI71506 had different alleles in eight of nine markers flanking the Rag 1 region. Only M_Satt220 was similar between both resistant sources. We screened resistant and susceptible bulks from F2:4 plants with bulk segregant analysis to find SSR markers associated with resistance in PI71506. Analyses of SSR markers have not identified any specific markers associated with aphid resistance. Understanding the inheritance and characteristics of the resistance exhibited by PI71506 will aid breeders in creating highly resistant adapted soybean varieties.