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Several Aspects of the Ecology and Pathology of Fusarium oxysporum f. sp. cepae. G. S. Abawi, Research Associate, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14850; J. W. Lorbeer, Associate Professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14850. Phytopathology 62:870-876. Accepted for publication 2 February 1972. DOI: 10.1094/Phyto-62-870.

A direct correlation was found between inoculum density of Fusarium oxysporum f. sp. cepae and damping-off of onion seedlings in artificially infested organic soil under controlled environment (26-C day and 21-C night; 60-70% relative humidity; 16-hr fluorescent light/day at 2,000 ft-c). A population of 5 × 10⁴ or more propagules/g of oven-dry soil was needed before significant disease development could be detected in field soil; 100 propagules caused extensive disease development in a sterilized soil. Seedling damping-off increased with temperature from 10 to 32 C. Poor germination occurred when conidia were added to field soil and germ tubes formed were either lysed or converted to chlamydospores, the form in which the fungus exists in organic soils cropped to onion. The fungus population decreased in the absence of onion and increased in its presence. Roots of Oxalis corniculata were heavily infected by the fungus when grown in artificially infested organic soils containing 5 × 10⁴ propagules/g of oven-dry soil.