Inheritance and gene mapping of resistance to soybean mosaic virus strain SC14 in soybean

Soybean mosaic virus (SMV) is one of the most broadly distributed diseases worldwide. It causes severe yield loss and seed quality deficiency in soybean (Glycine max (L.) Merr.). SMV Strain SC14 isolated from Shanxi Province, China, was a newly identified virulent strain and can infect Kefeng No. 1, a source with wide spectrum resistance. In the present study, soybean accessions, Pl96983, Qihuang No. 1 and Qihuang No. 22 were identified to be resistant (R) and Nannong 1138-2, Pixianchadou susceptible (S) to SC14. Segregation analysis of Pl96983 x Nannong 1138-2 indicated that a single dominant gene (designated as R-SC14) controlled the resistance to SC14 at both V-2 and R, developmental stages. The same results were obtained for the crosses of Qihuang No. 1 x Nannong 1138-2 and Qihuang No. 22 x Nannong 1138-2 as in Pl96983 x Nannong 1138-2 at V-2 stage, but at R, stage, the F-1 performed as necrosis (a susceptible symptom other than mosaic), F-2 segregated in a ratio of 1R:2N:1S, and the progenies of necrotic (N) F-2 individuals segregated also in R, N and S. It indicated that a single gene (designated as R-SC14Q, to be different from that of Pl96983) controlled the resistance to SC14, its dominance was the same as in Pl96983 x Nannong 1138-2 (without symptoms) at V-2 stage and not the same at R-1 stage. The tightly linked co-dominant simple sequence repeat (SSR) marker Satt334 indicated that all the heterozygous bands were completely corresponding to the necrotic F-2 individuals, or all the necrotic F-2 individuals were heterozygotes. It was inferred that necrosis might be due to the interaction among SMV strains, resistance genes, genetic background of the resistance genes, and plant development stage. Furthermore, the bulked segregant analysis (BSA) of SSR markers was conducted to map the resistance genes. In F-2 Of Pl96983 x Nannong 1138-2, five SSR markers, Sat_297, Sat_234, Sat_154, Sat_033 and Sat_120, were found closely linked to R-SC14, with genetic distances of 14.5 cM, 11.3 cM, 4.3 cM, 3.2 cM and 6 cM, respectively. In F-2 of Qihuang No. 1 x Nannong 1138-2, three SSR markers, Sat_234, Satt334 and Sct_033, tightly linked to R-SC14Q with genetic distances of 7.2 cM, 1.4 cM and 2.8 cM, respectively. Based on the integrated joint map by Cregan et al. (1999), both R-SC14 and R-SC14Q were located between Sat_234 and Sct_033 on linkage with group F of soybean, with their distances from Sct_033 at the same side being 3.2 cM and 2.8 cM, respectively. Therefore, R-SC14 and R-SC14Q might be on a same locus. The obtained information provides a basic knowledge for marker-assisted selection of the resistance gene in soybean breeding programs and fine mapping and map-based cloning of the resistance gene.