Physical map location of the Rps1-k allele in soybean

Several genetic maps of soybean [Glycine max (L.) Merr.] have been developed during the past decade. Different markers have been used to construct these maps including restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), and classical markers. However, virtually none of the maps and linkage groups developed has been associated with specific soybean chromosomes. For example, there are 13 single dominant resistance genes at 7 different loci that control Phytophthora sojae. These resistance genes (Rps genes) have not been located on any chromosomes, but several have been associated on classical and molecular maps. For example, the Rps1 locus is associated with molecular linkage group N. The objective of this study was to locate the Rps1 locus on a specific soybean chromosome using primary trisomic analysis. Crosses were made between 10 soybean trisomic lines and cv. Resnik (containing Rps1-k). The F₂ populations from trisomic parents were inoculated with race 3 of P. sojae to determine the ratio of resistant to susceptible plants. Nine of the F₂ populations tested segregated in a normal 3:1 ratio. The F₂ population of triplo 3 segregated in a 2:1 ratio, the expected segregation ratio for a single dominant gene if the gene is located on the extra chromosome, suggesting that the Rps1 locus is on chromosome 3. Thus, chromosome 3 corresponds to molecular linkage group N of the integrated genetic linkage map.