Formae Speciales and Races of Fusarium oxysporum Causing Wilts of the Cucurbitaceae

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Abstract
F. oxysporum f. sp. cucumerinum from the USA, Germany and Japan; f. sp. melonis from Canada, France, Israel, Japan and the USA, f. sp. niveum from Florida and South Carolina, USA; f. sp. lagenariae and f. sp. luffae from Japan were used, respectively, in inoculations of 16 cultivars or breeding lines of cucumber [Cucumis sativus], 49 of muskmelon [C. melo], 23 of watermelon [Citrullus lanatus] 8 of gourds [Lagenaria spp.] and 1 each of citron [Citrullus sp.] and colocynth [Citrullus colocynthis]. 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, lagernariae or luffae nor could the races of f. sp. niveum reported for the USA be clearly separated. In addition to the 4 clearly defined races of f. sp. melonis from France, 3 new races, i.e., race 5 from the USA-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 [Luffa aegyptiaca], 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.

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