Identification of SSR markers linked to partial resistance to soybean rust in Brazil from crosses using the resistant genotype IAC 100

Soybean rust is considered a highly aggressive disease in soybean crops. Most research has focused on obtaining resistant genotypes based on dominant or recessive alleles, which provide vertical resistance. The identification of promising crosses that may be used to develop genotypes with horizontal resistance from IAC 100 may help to increase the longevity of the recommended cultivars. However, this type of resistance is limited by environmental variables that may hinder selection. We ranked crosses based on their response to soybean rust using genetic estimates and predicted gains. It was also an objective to identify quantitative trait loci (QTLs) associated with resistance to soybean rust in two generations derived from the same cross. Eighty-seven F-4 progenies from IAC 100 (partial resistance) x BRS Caiaponia (susceptible) cross were field phenotyped. The data divided the DNA samples into two groups for bulked segregant analysis, which was carried out using simple sequence repeat (SSR) primers. A linkage map for the F-4 generation was obtained based on 29 SSR markers, which were distributed into nine linkage groups, covering 285.9 cM of the genome. Six QTLs were mapped in four of these groups and two of them were responsible for 39% of the phenotypic variance in resistance to soybean rust. The linkage map generated for the F-7 generation was similar to that of the F-4 generation, covering 266 cM. Four of the six QTLs mapped in the F-4 generation were also identified in the F-7 generation, showing that the genomic regions contributing to horizontal resistance to soybean rust are stable.