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Disease Note.

A Blight of Cucurbits Caused by Microdochium tabacinum. S. C. Bost, University of Tennessee, Box 110019, Nashville 37222. C. A. Mullins, Department of Plant and Soil Science, University of Tennessee, Route 9, Box 363, Crossville 38555. Plant Dis. 76:861. Accepted for publication 11 February 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0861C.

A blight of certain cucurbit crops occurred in several locations throughout Tennessee each year since 1988. The disease was characterized by light tan to "bleached," sunken, spindle-shaped lesions primarily on the main stems, petioles, main leaf veins, and peduncles and sometimes on the fruit and leaf blades. Individual lesions were less than 0.5 cm long but often coalesced to form a continuous dry, scabby surface. Stem infection caused death of leaves, and defoliation was almost total in severe cases. Results from field trials conducted in naturally infested sites indicated that the most susceptible cucurbit species is Cucurbita pepo L. (pumpkin, zucchini, yellow summer squash). Conidia of Microdochium tabacinum (Van Beyma) Arx (= Fusarium tabacinum (Van Beyma) W. Gams) (2) were present in all lesions examined. The pathogenicity of the fungus was confirmed by wound-inoculating pumpkin plants (cv. Howden's Field) with plugs of a single-spore culture grown on oatmeal agar. Typical discrete and continuous lesions formed around the inoculated wounds within 5 days during incubation in a growth chamber at 25 C and 100% relative humidity. M. tabacinum was reisolated from the lesions. Although M. tabacinum has been reported to cause a dieback of cucumber in the former U.S.S.R. (1), this is the first known report of M. tabacinum as a pathogen of cucurbit crops in the United Slates.

References: (1) M. V. Elbakyan. Inst. Zasheh. Rast. 29:tI6, 1910. (2) J. A. von Arx. Trans. Br. Mycol. Soc. 82:373, 1984.