Fine Mapping of Resistance Genes to SMV Strains SC6 and SC17 in Soybean

Abstract

SMV strains SC6 and SC17 were prevalent in the North China and the Yangtze Valleys soybean production regions. Two soybean cultivars Q0926 and Zhongdou 35, which were resistant to SC6 and SC17, were respectively crossed with Nannong 1138-2 and Nannongcaidou 5, which were susceptible to SC6 and SC17, to determine inheritance of resistance to SC6 or SC17. Q0926 was also crossed with Zhongdou 35 to study allelic relationships of the resistance genes from the two soybean cultivars. On the basis of the results, the resistance genes to SC6 and SC17 were fine mapped. The results showed that the F 1 plants presented complete resistance, F2 population were segregated with a ratio of 3R:1S, F2:3 population were segregated with a ratio of 1R:2Seg:1S in resistant (R)×susceptible (S) crosses. These results indicated that the resistances of Q0926 and Zhongdou 35 to SC6 and SC17 were controlled by a single dominant gene respectively. The F 1 plants displayed complete resistance, and F 2 populations of the crosses Q0926×Zhongdou 35 were not segregated, indicating that the resistance genes to SC6 and SC17 were allelesor very closely linked. Genetic maps showed that 25 SSR markers were linked to the resistance gene to SC6 (designated R SC6 ) and the genetic distance and order of the two closest SSR markers to R SC6 were BARCSOYSSR_02_0617 (0.775 cM)-R SC6BARCSOYSSR_02_0621 (0.519 cM). The 38 SSR markers were linked to the resistance gene to SC17 (designated R SC17 ) and the genetic distance and order of the two closest SSR markers to R SC17 were BARCSOYSSR_02_0622 (0.264 cM)-R SC17BARCSOYSSR_02_0627 (0.262 cM), their corresponding physical intervals were 52 kb and 60 kb. The studies on inheritance of resistance to SMV provide a theoretical guidance to programs of resistance breeding to SMV. Fine map of resistance genes laid the foundation for molecular marker-assisted selection and map-based cloning of resistance genes.