Fine Mapping of Resistance Genes from Five Brown Stem Rot Resistance Sources in Soybean

Brown stem rot (BSR) of soybean [Glycine max (L.) Merr.] caused by Cadophora gregata (Allington & Chamb.) T.C. Harr. & McNew can be controlled effectively with genetic host resistance. Three BSR resistance genes Rbs1, Rbs2, and Rbs3, have been identified and mapped to a large region on chromosome 16. Marker‐assisted selection (MAS) will be more efficient and gene cloning will be facilitated with a narrowed genomic interval containing an Rbs gene. The objective of this study was to fine map the positions of Rbs genes from five sources. Mapping populations were developed by crossing the resistant sources ‘Bell’, PI 84946‐2, PI 437833, PI 437970, L84‐5873, and PI 86150 with either the susceptible cultivar Colfax or Century 84. Plants identified as having a recombination event near Rbs genes were selected and individually harvested to create recombinant lines. Progeny from recombinant lines were tested in a C. gregata root‐dip assay and evaluated for foliar and stem BSR symptom development. Overall, 4878 plants were screened for recombination, and progeny from 52 recombinant plants were evaluated with simple‐sequence repeat (SSR) genetic markers and assessed for symptom development. Brown stem rot resistance was mapped to intervals ranging from 0.34 to 0.04 Mb in the different sources. In all sources, resistance was fine mapped to intervals inclusive of BARCSOYSSR_16_1114 and BARCSOYSSR_16_1115, which provides further evidence that one locus provides BSR resistance in soybean.