Inheritance of Resistance to Downy Mildew in Cucumis melo. C. E. Thomas, Research Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, U.S. Vegetable Laboratory, Charleston, SC 29407. Y. Cohen, J. D. McCreight, E. L. Jourdain, and S. Cohen. Professor, Department of Life Sciences, Bar-Ilan University, Ramat Gan, Israel; Research Horticulturist, U.S. Department of Agriculture, Agricultural Research Service, U.S. Agricultural Research Station, Salinas, CA 93905; Horticulturist, U.S. Department of Agriculture, Agricultural Research Service, U.S. Vegetable Laboratory, Charleston, SC 29407; and Graduate Research Assistant, Department of Life Sciences, Bar-Ilan University, Ramat Gan, Israel.. Plant Dis. 72:33-35. Accepted for publication 30 June 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/PD-72-0033.

The F₁, F₂, and BC₁ from reciprocal crosses of the downy mildew-resistant, inbred muskmelon line MR-1, developed from Cucumis melo PI 124111, and the susceptible cultivar Ananas Yokneam were used to determine inheritance of resistance to downy mildew incited by Pseudoperonospora cubensis. The reactions of the parental lines and progenies to sporangial inoculation with P. cubensis support the hypothesis that the resistance of line MR-1 is conferred by two incompletely dominant genes designated Pc1 and Pc2. F₂ phenotypic ratios were 6 susceptible:9 moderately resistant:1 resistant. The BC₁ to the resistant parent had a phenotypic ratio of 3 moderately resistant:1 resistant and the BC₁ to the susceptible parent segregated 3 susceptible:1 moderately resistant. The resistance to downy mildew in line MR-1 is expressed as the production of reaction type 4 lesions in response to challenge by P. cubensis.

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