VIEW ARTICLE

Ecology and Epidemiology

Biocontrol of Fusarium Wilt of Cucumber Resulting from Interactions Between Pseudomonas putida and Nonpathogenic Isolates of Fusarium oxysporum. Chang- Seuk Park, Visiting scientist, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523, Present address: Department of Plant Protection, Gyoeonsang National University, Jinju, 620, Gyeongnam, South Korea; T. C. Paulitz(2), and Ralph Baker(3). (2)Visiting scientist, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523, (2)Present address: USDA-ARS, Horticultural Crops Research Lab, 3420 NW Orchard Ave., Corvallis, OR 97330; (3)Professor, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. Phytopathology 78:190-194. Accepted for publication 11 August 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-190.

Fluorescent pseudomonads and nonpathogenic isolates of Fusarium oxysporum were effective in inducing suppressiveness to Fusarium wilt of cucumber when added to soil together (pH 6.7) but ineffective when added separately. Suppressiveness by such combination treatments was enhanced in nearly neutral (pH 6.7) to alkaline soils (pH 8.1), in comparison with acid soil (pH 5.5). Strains of fluorescent pseudomonads reduced the germination of chlamydospores of nonpathogenic and pathogenic isolates of F. oxysporum in the rhizospheres of cucumber plants. Population densities of fluorescent pseudomonads increased significantly in the rhizosphere of cucumber in the presence of a nonpathogenic isolate of F. oxysporum in soil of pH 8.1. It is hypothesized that the activity of fluorescent pseudomonads and their siderophore production are enhanced by increased root exudates induced by relatively high population densities of nonpathogenic isolates of F. oxysporum. This, in turn, leads to competition for iron, which is essential for successful germination of the pathogen and penetration of the host.