VIEW ARTICLE

Genetics

Genetics of Resistance to Physiologic Races of Phytophthora megasperma var. sojae in the Soybean Cultivar Tracy. K. L. Athow, Professor and associate professor of Plant Pathology, Purdue University, West Lafayette, IN 47907; F. A. Laviolette(2), and J. R. Wilcox(3). (2)Professor of Agronomy, Purdue University, West Lafayette, IN 47907; (3)Research geneticist, Agricultural Research, Science and Education Administration, U. S. Department of Agriculture. Phytopathology 69:641-642. Accepted for publication 28 December 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-641.

Inheritance of resistance to Phytophthora megasperma var. sojae was studied in the F₂ and F₃ generations from the cross of the soybean cultivar Tracy (resistant to all nine reported physiologic races) with PI 360952 (susceptible to all races). The F₂ populations segregated in a 3:1 ratio of resistant/susceptible to races 2, 6, and 7 and segregated in a 15:1 ratio of resistant/susceptible to races 1, 3, 4, 5, 8, and 9. Data from F₂ plants, substantiated by the disease reaction of their F₃ progenies, indicated two independent, dominant genes for resistance in Tracy. One gene controls resistance to races 1, 2, 3, 4, 5, 8, and 9. It apparently was derived from PI 171442, a progenitor of Tracy, which has the gene Rps₃ and is resistant to all races but 6 and 7. The other gene for resistance in Tracy probably derived from D60-9647, the other parent of Tracy, which has the gene Rps^b₁ and is resistant to all races but race 2. Lines presumably with the genotype Rps^b₁ Rps^b₁ Rps₃ Rps₃ were selected that are resistant to the nine races of the pathogen and are adapted to the Midwest.