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Biocontrol of Botrytis cinerea in Strawberry Leaves. J. C. Sutton, Department of Environmental Biology, University of Guelph, Guelph, ON N1G 2W1, Canada; G. Peng, Department of Environmental Biology, University of Guelph, Guelph, ON N1G 2W1, Canada, Present address: Ontario Ministry of Agriculture and Food, P. O. Box 340, Stirling K0K 3E0, Canada. Phytopathology 83:615-621. Accepted for publication 12 February 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-615.

In biocontrol tests, strawberry leaves were inoculated with Botrytis cinerea, were treated 25 wk later with antagonistic fungi or with chlorothalonil, and were kept on paraquat-chloramphenicol agar (PCA) or were sprayed with paraquat to kill the tissues and allow the pathogen to sporulate. Gliocladium roseum, a Penicillium sp., and Trichoderma viride suppressed the number of conidiophores of B. cinerea by 97100% in attached leaves in the greenhouse. The antagonists also suppressed sporulation incidence of the pathogen by 58, 64, and 48%, respectively, in semisenescent overwintered leaves in field plots and by 81100, 59100, and 5387%, respectively, in green leaves in field plots. G. roseum suppressed the pathogen as effectively as did chlorothalonil in all tests, and Penicillium sp. and T. viride were as effective in the greenhouse and in three of six field tests. Biosuppression generally increased as temperature increased from 10 to 25 C, but only G. roseum was highly suppressive at 10 and 15 C. Germination rate of conidia and growth of germ tubes of each antagonist on the leaves increased with temperature. When applied to infected green leaves and incubated on PCA, the antagonists suppressed hyphal growth of B. cinerea in leaf tissues. Hyperparasitism was not observed in leaves or in a separation-membrane assay. The antagonists markedly suppressed the number of conidiophores of B. cinerea when applied after the leaves had been incubated on PCA for 0 or 24 h but only slightly or not at all in leaves incubated on PCA for 48 or 72 h. G. roseum also was nonsuppressive in leaves that had died naturally. The antagonists suppressed B. cinerea primarily when applied to living green leaves.

Additional keywords: Fragaria ananassa, gray mold, Myrothecium verrucaria, Rhodotorula glutinis, substrate competition.