Genetic-Relationships Among Plant Introductions For Resistance To Soybean Cyst-Nematode Race-5

Three soybean [Glycine max (L.) Merr.] plant introductions (PD 399061, PI 424595, and PI 438342 were recently identified as resistant to Race 5 of the soybean cyst nematode (SCN) Heterodera glycines Ichinohe. Plant breeders need to know if these plant introductions have the same or different genes for resistance than those in previously identified resistant plant introductions. Crosses were made between the Race 5 resistant plant introductions and progenies were tested for segregation for resistance to the nematode. Crosses between the three plant introductions and susceptible Tracy-M' soybean were made to estimate the number of genes involved in resistance to SCN Race 5. There was no segregation in Pa progenies in crosses among resistant PI 424595, PI 438342, 'Peking', PI 90763, and PI 437654. A few susceptible progenies were found from crosses of resistant genotypes 'Cordell' or PI 399061 with the other resistant genotypes. Ah the resistant genotypes appear to have the same genes for SCN Race 5 resistance at most loci, but PI 399061 probably differs in resistance genes from other resistant genotypes at one or more loci. Data from crosses of Tracy-M with PI 399061, PI 424595, and PI438342 indicate resistance is controlled by three or more genes.