Investigating the genetic model for brown stem rot resistance in soybean

Genetic analyses have indicated that brown stem rot (BSR) resistance in soy bean is conferred by dominant alleles at three independent loci, the action s of which may be modified by linked or independent loci. A study was condu cted to characterize the inheritance of BSR resistance in PI 567609, a soyb ean plant introduction from China. Segregating progeny from crosses of PI 5 67609 with BSR-susceptible and -resistant genotypes were evaluated for resp onse to BSR-causal fungus, Phialophora gregata, Genetic analyses indicated that PI 567609 carries a single gene or cluster of linked genes for brown s tem rot resistance, and that this gene (or cluster) is allelic to, or tight ly linked to previously identified resistance genes, Rbs1, Rbs2, and Rbs3 B ecause previous allelism tests indicated that Rbs1, Rbs2 and Rbs3 were unli nked, and molecular mapping studies have indicated that Rbs1, Rbs2, and Rbs 3 are linked on molecular linkage group J of soybean, a new model is propos ed for BSR resistance. In this model, BSR resistance is controlled through the interaction of alleles at four independent loci, at least two of which are necessary to condition a resistance response. Functional redundancy at three of these loci allows any one of the three to interact with a fourth l ocus to confer resistance to BSR.