Two major recessive soybean genes conferring soybean rust resistance

Soybean rust (SBR) caused by Phakopsora pachyrhizi Syd. is currently the most threatening fungal disease of soybean [Glycine max (L.) Merr.] in the Americas. Development of resistant or tolerant cultivars is a major goal in several soybean breeding programs. Four loci, all carrying dominant alleles that confer a resistant phenotype, have been described. We investigated the genetic basis of the resistance in PI 200456 and PI 224270 by crossing each of them with a susceptible cultivar (CD 208). Phenotypic segregation ratios for F-2 plants and F-2.3 lines showed that the resistance in each resistant parent was controlled by a single recessive gene. A test for allelism demonstrated that these genes are non-allelic. This is the first report of recessive genes controlling SBR resistance in soybean and may represent a different type of resistance for breeding programs aimed at development of more durable resistance.