BIOLOGICAL CONTROL OF WHITE ROT OF ONION .I. INTERACTIONS OF SOIL MICRO-ORGANISMS WITH SCLEROTIUM CEPIVORUM BERK

Interactions of 123 isolates of fungi, 17 of bacteria and 22 of actinomycetes, respectively, with Sclerotium cepivorum were studied in agar culture. They were grouped into 4 different types of reactions. Amongst them Trichoderma viride, Fusarium graminearum, Coniothyrium minitans and Gliocladium roseum inhibited the growth of S. cepivorum and later grew over its colony. T. viride showed a characteristic coiling around the hyphae of S. cepivorum. T. viride and F. graminearum prevented the development of sclerotia. C. minitans was found to parasitize the sclerotia of S. cepivorum and produced its pycnidia within them. Aleurisma carnis, Cladosporium elatum, Penicillium expansum, P. nigricans, P. notatum, P. piscarium, P. puberulum, P. rolfsii, P. urticae, P. variabile, Tilachlidium humicola and Helminthosporium sp. inhibited the growth of S. cepivorum at a distance. Eleven isolates of bacteria and 3 of Streptomyces sp. showed pronounced antagonistic properties against S. cepivorum. Experiments were carried out to study the effects on white rot development in soil of organisms selected from agar plate tests. None of the antagonistic micro organisms had any deleterious effects on onion growth. Of the organisms tested P. nigricans gave the best results in controlling white rot infection. © 1969 Dr. W. Junk N.V.