Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2001
Publication Date: 11/1/2001
Citation: Gardner, M.E., Hymowitz, T., Xu, S.J., Hartman, G.L. 2001. Physical map location of the rps1-k allele in soybean. Crop Science. 41:1425-1438. Interpretive Summary: Phytophthora root rot of soybean is caused by the soilborne fungus Phytophthora sojae. In 1994, Phytophthora root rot ranked third in the U.S. in yield-reducing diseases of soybean. Genetic resistance is one of the most effective methods of controlling Phytophthora root rot. The major sources of resistance are a series of single dominant genes. These resistance genes (Rps genes) have not been located on any soybean chromosomes. The objective of this study was to locate the Rps1 locus on a specific soybean chromosome using a certain type of genetic (trisomic) analysis. Populations of resistance by susceptible crosses indicated that the resistant gene is located on chromosome 3. This data provides the first physical map location on a soybean chromosome of a resistance gene in soybean. This information is useful to both breeders and pathologists that conduct research on developing resistance to this fungus.
Technical Abstract: Several genetic maps of the soybean have been developed during the past decade. Different markers have been used to construct these maps including RFLP, AFLP, RAPD, 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.