Effect of Ulocladium atrum and other antagonists on sporulation of Botrytis cinerea on dead lily leaves exposed to field conditions.
The potential of Aureobasidium pullulans, Chaetomium globosum, Gliocladium catenulatum and U. atrum to suppress sporulation of B. cinerea was tested in 9 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 with 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 temp. during leaf wetness periods. Germ tube length, determined 5-6 d after application, increased with total leaf wetness duration unless individual wetness periods were short. C. globosum reduced sporulation of B. cinerea in only 3 of 9 experiments. A pullulans, G. catenulatum and a mixture of the fungicides chlorothalonil and maneb did not suppress sporulation of B. cinerea. It is suggested that the differential effect of the antagonists may mainly be caused by differences in response to the microclimatic conditions. It is concluded that the high saprophytic competitive ability of U. atrum under various microclimatic conditions makes this fungus a candidate for the development of a biological control product aimed at suppression of sporulation of Botrytis spp. on necrotic leaf tissue. It is thought that this is the first report of U. atrum as an antagonist of Botrytis spp.