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Effect of Ulocladium atrum and Other Antagonists on Sporulation of Botrytis cinerea on Dead Lily Leaves Exposed to Field Conditions. J. Köhl, DLO Research Institute for Plant Protection (IPO-DLO), P.O. Box 9060, 6700 GW Wageningen, the Netherlands; W. M. L. Molhoek, C. H. van der Plas, and N. J. Fokkema. DLO Research Institute for Plant Protection (IPO-DLO), P.O. Box 9060, 6700 GW Wageningen, the Netherlands. Phytopathology 85:393-401. Accepted for publication 24 November 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-393.

The potential of the antagonistic fungi Aureobasidium pullulans, Chaetomium globosum, Gliocladium catenulatum, and Ulocladium atrum to suppress sporulation of Botrytis cinerea was tested in nine experiments on dead lily leaves exposed to varying microclimatic conditions in the field. U. atrum competed successfully with naturally occurring saprophytes, mainly Cladosporium spp., colonized the dead lily leaves, survived dry periods, and consistently reduced sporulation of naturally occurring B. cinerea. U. atrum reduced the area of the leaf surface covered with conidiophores of B. cinerea by 80–96% compared to the control treated only with water. Germination rates of conidia of U. atrum, determined 18 h after field application, varied between 0 and 99%, depending on duration of leaf wetness periods, which ranged from 0 to 18 h, and on temperatures during leaf wetness periods. Germ tube length, determined 5–6 days after application, increased with total leaf wetness duration unless individual wetness periods were short. C. globosum reduced sporulation of B. cinerea only in three of nine experiments. A. pullulans, G. catenulatum, and a mixture of the fungicides chlorothalonil and maneb did not suppress sporulation of B. cinerea. The differential effect of the antagonists may mainly be caused by differences in response to the microclimatic conditions. The high saprophytic competitive ability of U. atrum under various microclimatic conditions makes this fungus an attractive candidate for the development of a biological control product aimed at suppression of sporulation of Botrytis spp. on necrotic leaf tissue. To our knowledge, U. atrum has not been described as an antagonist of Botrytis spp. or other fungal plant pathogens.

Additional keywords: inoculum production, microbial ecology.