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Colonization of Crop Residue by Fusarium oxysporum f. sp. melonis and Other Species of Fusarium. T. R. Gordon, Assistant professor, Department of Plant Pathology, University of California, Berkeley 94720; D. Okamoto, staff research associate, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 80:381-386. Accepted for publication 2 November 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-381.

Colonization of decomposing roots, and shoot tissue buried in field soil, by the muskmelon wilt pathogen race 2 of Fusarium oxysporum f. sp. melonis was quantified as colony-forming units per gram of tissue. Colonization of the same substrates by F. equiseti, F. solani, and nonpathogenic F. oxysporum was also quantified. F. o. melonis was isolated from roots of the following seven crops both before and 5 days after shoots were severed at the soil line: the muskmelon cultivar PMR-45 (susceptible to Fusarium wilt), the muskmelon cultivar Greenflesh Honey Dew (resistant to Fusarium wilt under field conditions), alfalfa, tomato, sugar beet, cotton, and wheat. The proportion of total root colonization represented by each of the four fungi was the same before and after shoot removal except that, under some conditions, F. equiseti represented a significantly greater proportion of total colonization after shoot removal. Averaged over seven different residue sources (i.e., crops), population densities of F. o. melonis on buried shoot tissue were greater than those of nonpathogenic F. oxysporum. This difference could not be attributed to differences in soil inoculum density of the two fungi or to prior colonization of the shoot tissue by F. o. melonis.

Additional keywords: soilborne pathogen.