The first report of the interaction between race 17 of Phytophthora megasperma f. sp. glycinea (Pmg) and the Rpsl-b allele was made by Keeling (1982) in his initial report on this race. Keeling (1982) reported that 'Sanga' (Rpsl-b) gave a resistant response to race 17, but that PI 171442 (Rps3) and 'Tracy', which possesses the Rpsl-b and Rps3 alleles (Athow et al., 1979), gave a susceptible response. The relative responses of Tracy and Sanga were unexpected, since, in all cases studied to date, an Rps allele for resistance is epistatic to Rps alleles for susceptibility at any loci (e.g., Athow et al., 1980; Layton et al., 1984; Ploper et al., 1985; Athow et al., 1986).