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Disease Control and Pest Management

Airborne Spore Dispersal and Recolonization of Steamed Soil by Fusarium oxysporum in Tomato Greenhouses. Randall C. Rowe, Assistant Professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center, and The Ohio State University, Wooster, OH 44691; James D. Farley(2), and David L. Coplin(3). (2)(3)Associate Professor, and Assistant Professor, respectively, Department of Plant Pathology, Ohio Agricultural Research and Development Center, and The Ohio State University, Wooster, OH 44691. Phytopathology 67:1513-1517. Accepted for publication 20 June 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1513.

A crown and root rot of greenhouse tomatoes caused by Fusarium oxysporum has become a problem in Ohio and Ontario, Canada, during the past few years. Repeated attempts to control the disease by steam-disinfestation of soil have failed. In naturally infested commercial greenhouses, microconidia of pathogenic isolates of F. oxysporum were trapped from air. The sources of these airborne microconidia were presumed to be infected tomato stems, straw mulch, and partially decomposed tomato vines in outside dump piles; large numbers of microconidia were recovered from all of these substrates. Flats of autoclaved soil were atomized with suspensions of microconidia to determine their recolonization rate in steamed soil. The number of propagules per gram of soil increased by 103 after 3 days and by 104 after 1 wk. After 2 wk, populations stabilized at about 1,000/g of soil, regardless of initial inoculum concentrations. This investigation suggests that the failure of soil steaming to control Fusarium crown and root rot was due to recontamination of freshly steamed soil by airborne microconidia of the pathogen.

Additional keywords: Fusarium crown and root rot, epidemiology.