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Inheritance of Resistance to Alternaria cucumerina in Cucumis melo Line MR-1. C. E. Thomas, Research Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, U.S. Vegetable Laboratory, Charleston, SC 29414. J. D. McCreight, and E. L. Jourdain. Research Horticulturist, U.S. Department of Agriculture, Agricultural Research Service, U.S. Agricultural Research Station, Salinas, CA 93905; and Horticulturist, U.S. Department of Agriculture, Agricultural Research Service, U.S. Vegetable Laboratory, Charleston, SC 29414. Plant Dis. 74:868-870. Accepted for publication 16 March 1990. 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, 1990. DOI: 10.1094/PD-74-0868.

The resistant reaction of muskmelon line MR-1 to Alternaria leaf blight is characterized by the production of small necrotic lesions in response to infection by the pathogen. These lesions remain restricted and do not expand to support abundant sporulation, as is the case with susceptible cultivars. The F₁, F₂, and BC₁ from crosses of the Alternaria leaf blight-resistant inbred line MR-1 and the susceptible cultivars Perlita and PMR 6 were used to determine inheritance of resistance to Alternaria cucumerina. All plants in the F₁ populations were resistant. F₂ phenotypic ratios were 3 resistant:1 susceptible. The BC₁ to the resistant parent populations were all resistant and the BC₁ to the susceptible parent segregated 1 resistant:1 susceptible. The reactions of parental lines and progenies to conidial inoculation with A. cucumerina support the hypothesis that the resistance of line MR-1 is conferred by a single dominant gene designated Ac.