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Genetics

A New Allele at the Rps3 Locus for Resistance to Phytophthora megasperma f. sp. glycinea in Soybean. L. D. Ploper, Graduate research assistant, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; K. L. Athow(2), and F. A. Laviolette(3). (2)(3)Professor, and associate professor, respectively, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 75:690-694. Accepted for publication 23 January 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-690.

The genetics of resistance to Phytophthora megasperma f. sp. glycinea was studied in soybean (Glycine max) PI 172901, which was resistant to races 1 through 16 of the pathogen. PI 172901 was crossed to Harosoy (rps), Mukden (Rps1), Sanga (Rps1b), Wells II (Rps1c), Williams 82 (Rps1k), PI 86972-1 (Rps3), PRX27-108 (Rps1 Rps4), and Altona (Rps6). The F2 populations and the progenies of F2 plants from each cross were evaluated for their reaction to physiologic races 1, 2, 3, 4, 5, 7, and 9 of the fungus. The results showed that there were two independent, dominant genes for resistance in PI 172901. One was Rps1b which gives resistance to races 1, 3, 4, 5, 7, and 9, and susceptibility to race 2. The other gene was an undescribed allele at the Rps3 locus which confers resistance to the seven physiologic races included in this study. The symbol Rps3b was proposed for this gene to indicate a second allele at the Rps3 locus and to discriminate it from the gene Rps3 which conditions susceptibility to race 7.