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Inheritance of Resistance to Four Physiologic Races of Phytophthora megasperma var. sojae. E. H. Mueller, Graduate Research Assistant, Purdue University, West Lafayette, IN 47907; K. L. Athow(2), and F. A. Laviolette(3). (2)(3)Professor, and Associate Professor of Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 68:1318-1322. Accepted for publication 18 April 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1318.

The F2 populations and F3 progenies from 10 soybean crosses were tested with physiologic races 1, 2, 3, and 4 of Phytophthora megasperma var. sojae. The soybean cultivars and plant introductions, Harosoy (susceptible to races 1, 2, 3, and 4), Mukden (resistant to races 1 and 2; susceptible to races 3 and 4), P.I. 54615-1 (resistant to races 1, 2, and 3; susceptible to race 4), P.I. 84637 (resistant to races 1, 3, and 4; susceptible to race 2), and P.I. 86972-1 (resistant to races 1, 2, 3, and 4) were selected as parents based on their reaction to the four races of the pathogen and each one was crossed to the other four. The data indicate that the resistance of Mukden, P.I. 54615-1, and P.I. 84637 is controlled by a different single dominant allele in each located at the same locus. To differentiate these alleles it is suggested that the allele in P.I. 54615-1 be designated Rpsc and the allele in P.I. 84637 be changed from rps12 to Rpsb to from the allelomorphic series Rpsa, Rpsb, Rpsc, and rps, represented by Mukden, P.I. 84637, P.I. 54615-1, and Harosoy, respectively. The data further indicate that the resistance of P.I. 86972-1 is controlled by a single dominant allele located at a different locus. It is suggested that this allele provisionally be designated Rps3.

Additional keywords: soybean disease.