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Evidence that Antagonistic Bacteria Suppress Fusarium Wilt of Celery in Neutral and Alkaline Soils. D. C. Opgenorth, Former graduate research assistant, Department of Plant Pathology, University of California, Riverside 92521, Current address: Department of Food and Agriculture, Analysis and Identification, 1220 N Street, Sacramento, CA 95814; R. M. Endo, professor, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 73:703-708. Accepted for publication 1 December 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-703.

The severity of Fusarium yellows of celery was increased significantly as the pH of U.C. soil mix was reduced from 8.3 to 3.9. Chlamydospore germination of Fusarium oxysporum f. sp. apii in 0.1 M citrate buffer was maximal at pH 7.1, but no significant difference in germination occurred between pH 3.3 and 9.6. Dry weights of the fungus after 1 wk of growth in nutrient broth were maximal at pH 4.0 and 9.6. In cultures coinoculated with Corynebacterium sp., maximal growth of mycelial mats of F. oxysporum f. sp. apii occurred at pH 4.0; growth was significantly less at pH 6.2 and 7.3 than at 5.1. When the pathogen was grown in dual culture with each of 24 different bacterial isolates from four soil types, the number of bacterial isolates that did not allow significant mycelial growth increased from 16 to 54 and 75% as the pH of nutrient broth was increased from 5.1 to 6.2 and 7.3, respectively. When chlamydospores were germinated in buffered and pH-adjusted nutrient broth previously inoculated with Corynebacterium sp., germination after 2 days was significantly less than that of the sterile control at pH 5.1 or above. In a Noble agar medium adjusted to pH 5.7 or 6.9, the number of germ tubes originating from chlamydospores impinging on celery root tips was significantly greater in roots treated with streptomycin, as compared with roots treated with the active Corynebacterium culture.