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Etiology

Formae Speciales and Races of Fusarium oxysporum Causing Wilts of the Cucurbitaceae. G. M. Armstrong, Department of Plant Pathology, University of Georgia College of Agriculture Experiment Stations, Georgia Station, Experiment, GA 30212; Joanne K. Armstrong, Department of Plant Pathology, University of Georgia College of Agriculture Experiment Stations, Georgia Station, Experiment, GA 30212. Phytopathology 68:19-28. Accepted for publication 3 May 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-19.

Fusarium oxysporum f. sp. cucumerinum from the U.S., Germany, and Japan; f. sp. melonis from Canada, France, Israel, Japan, and the U.S.; f. sp. niveum from Florida and South Carolina; f. sp. lagenariae and f. sp. luffae from Japan were used, respectively, in inoculations of 16 cultivars or breeding lines of cucumber, 49 of muskmelon, 23 of watermelon, eight of gourds, and one each of citron and colocynth. Variations in virulence for a specific host occurred, but each forma specialis showed sufficient selective pathogenicity for the host from which it was derived to be retained as a valid forma specialis. No races were identified with ff. sp. cucumerinum, lagenariae, or luffae, nor could the races of f. sp. niveum reported from the U.S. be clearly separated. In addition to the four clearly defined races of f. sp. melonis from France, three new races; viz., race 5 from the U.S.-Canada, race 6 from Israel, and race 7 from Japan, were found among the 24 isolates in the collection of f. sp. melonis. Fifty other different wilt fusaria were nonpathogenic on a cultivar of cucumber, muskmelon, watermelon, and dishrag gourd, each of which was susceptible to its respective forma specialis. A forma specialis causing wilt of cucumber, muskmelon (race 5), watermelon, and dishrag gourd, respectively, was nonpathogenic on plants of 46 other species and cultivars that have been helpful in differentiating formae speciales and races of F. oxysporum.