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Ecology and Epidemiology

Physiological Specialization in Pseudoperonospora cubensis. C. E. Thomas, Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, U.S. Vegetable Laboratory, Charleston, SC 29407; T. Inaba(2), and Y. Cohen(3). (2)Plant pathologist, Shikoku National Agricultural Experiment Station, Zentsuji, Kagawa 765, Japan; (3)Professor, Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52 100, Israel. Phytopathology 77:1621-1624. Accepted for publication 28 May 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, 1987. DOI: 10.1094/Phyto-77-1621.

Controlled inoculation studies were conducted using local isolates of Pseudoperonospora cubensis in Israel, Japan, and the United States. Inoculations to 26 cultivars representing 13 species and subspecies within seven genera of the family Cucurbitaceae revealed distinct physiological specialization among isolates. Five pathotypes of P. cubensis could be distinguished based on high compatibility with specific hosts. All five pathotypes were highly compatible with Cucumis sativus and C. melo var. reticulatus. Pathotype 1 was highly compatible with them only. Pathotype 2 was highly compatible with these hosts and C. m. var. conomon. Pathotype 3 was highly compatible with these three species and subspecies plus C. m. var. acidulus. Pathotype 4 was highly compatible with all of the aforementioned hosts plus Citrullus lanatus. Pathotype 5 was highly compatible with all hosts mentioned above plus Cucurbita spp.