Identification and characterization of resistance to soybean aphid in 22 highly resistant soybean accessions

The soybean aphid is one of the main damaging pests of soybean. Host resistance can effectively reduce the loss caused by the damage of soybean aphid. There are abundant soybean germplasm in China, however, few aphid resistant soybeans were identified and genetic backgrounds of them were poorly characterized. In this study, 22 soybean accessions with high soybean aphid resistance (resistant rating of 1) were identified from 1469 accessions by evaluation in the net house. Detailed evaluation of aphid resistance revealed that all of these 22 soybeans possess good resistance when infested with three initial densities of aphids (2, 10, and 50 aphids per plant). Sixteen SSR markers flanking the published aphid resistance genes including Rag1, rag1b, rag1c, Rag2, Rag3, Rag3b, Rag3d, Rag3e, rag3, rag4 and Rag5 had been identified. Meanwhile, SNPs of these 22 highly resistant soybeans and 11 check accessions carrying known Rag genes were genotyped by a genome-wide genotyping array containing 158,327 SNPs. These SSR markers and SNPs flanking Rag genes were then used to characterize the aphid resistance in the identified resistant soybeans. Fourteen of these accessions were found to carry resistance gene Rag2, six accessions carry Rag2 and Rag3/Rag3b/Rag3d/rag3, and one accession carries Rag1/rag1c and Rag2. Another one accession probably has novel aphid resistance genes since it harbors unique haplotype in the interval containing all tested Rag genes. These highly aphid resistant accessions and the information of aphid resistant loci provide valuable sources for further isolation of aphid resistance genes and breeding aphid resistant soybean cultivars.