The Use of Nitrate-Nonutilizing Mutants and a Selective Medium for Studies of Pathogenic Strains of Fusarium oxysporum. Esther Hadar, Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100, Israel. J. Katan, and Talma Katan. Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100, Israel, and Department of Plant Pathology, ARO, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel. Plant Dis. 73:800-803. Accepted for publication 24 March 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0800.

A chlorate-containing selective medium was developed for tracing chlorate-resistant, nitrate-nonutilizing (nit) mutants of pathogenic strains of Fusarium oxysporum. Neither wild-type strains of Fusarium spp. nor most of the fungi from six field soils could grow on this medium, whereas most nit mutants of six formae speciales grew on it. The nit mutants retained their pathogenicity. Survival in soil of nit mutants belonging to three formae speciales was comparable to that of their wild-type parents. The use of labeled nit mutants, combined with the chlorate-containing selective medium, can facilitate ecological studies of pathogenic strains of F. oxysporum.