VIEW ARTICLE

Ecology and Epidemiology

Suppression of Fusarium roseum ‘Avenaceum’ by Soil Microorganisms. Y. S. Lin, Research assistant, Department of Plant Pathology, Washington State University, Pullman, WA 99164; R. J. Cook, plant pathologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Washington State University, Pullman, WA 99164. Phytopathology 69:384-388. Accepted for publication 15 October 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-384.

Fusarium roseum ‘Avenaceum’ is a highly virulent root pathogen of lentils, but severity of disease is suppressed by natural soil. The suppressive effect of natural soil was eliminated by moist heat (60 C for 30 min) treatment, but not by soil treatment with Bay 22555, pentachloronitro-benzine, or benomyl. Suppression was less apparent when the dosage of inoculum of Avenaceum was increased in soil. Within 8 wk the suppressivity gradually returned to heat-treated soil exposed to airborne contaminants; it returned immediately to treated soil amended with 1% (w/w) nontreated soil. The suppressive effect could not be attributed to induced host resistance. Instead, antagonists were shown to act against Avenaceum in the inoculum substrate in soil. Inoculum that had been buried 48–72 hr in nontreated soil, then transferred to heat-treated soil, no longer produced disease or supported growth of Avenaceum from the food base into the soil as did similar inocula from treated soil. Isolations from the inoculum substrate recovered from nontreated soil yielded species of common, fast-growing fungi; these included Mucor plumbeus, Mucor hiemalis, Trichoderma viride, and Penicillium spp. which singly and in combinations controlled lentil root rot caused by Avenaceum when added to treated soil. In contrast, several other isolates of soilborne fungi and bacteria did not control the disease. The inhibition of Avenaceum in the inoculum food base apparently was due to competition between Avenaceum and certain common, fast-growing fungi for the food base needed by Avenaceum to produce disease.