VIEW ARTICLE

The Behavior of Fusarium oxysporum f. sp. melonis in the Presence and Absence of Host Plants. Z. Banihashemi, Former Graduate Student, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823, Present address senior author: Associate Professor, Department of Plant Protection, College of Agriculture, Pahlavi University, Shiraz, Iran.; D. J. deZeeuw, Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Phytopathology 65:1212-1217. Accepted for publication 19 May 1975. DOI: 10.1094/Phyto-65-1212.

Both the rhizosphere population and the colonization of roots of susceptible host plants by Fusarium oxysporum f. sp. melonis increased with time. The increase in population was caused mainly by sporulation on infected roots. The population of F. oxysporum f. sp. melonis and other fungi was greater in the rhizosphere of wilted host plants than in the rhizosphere of healthy plants. The pathogen was able to colonize roots of many nonhost plants under field conditions, but there was no accompanying increase of F. oxysporum f. sp. melonis in soil. The population of F. oxysporum f. sp. melonis in soil increased in the presence of a living host and decreased in its absence, and was greater at the site of wilted plants and on the soil surface than between rows and at lower soil levels. Sporulation of the pathogen on infected vines and the sloughing away of decomposing infected tissues contributed to the increase in population on the soil surface, and to the root-zone effect at the lower depths. Infected vines were an important source of overwintering of the pathogen. In Michigan, the population of F. oxysporum f. sp. melonis was not greatly affected by low winter temperatures, but declined sharply in spring with the advent of milder weather. The drop in population was assumed to coincide with the progressive decomposition of infected plant residues.