Biocontrol of Botrytis cinerea by Ulocladium atrum in different productionsystems of cyclamen

Ten experiments in six different commercial greenhouses were conducted to s tudy the effect of spraying conidial suspensions of the saprophytic fungus Ulocladium atrum (1 x 10(6) conidia per mi) on infection of leaves and flow er petioles of cyclamen by Botrytis cinerea (gray mold). The greenhouses re presented the range of Dutch growing systems of cyclamen, differing conside rably in the arrangement of plants, irrigation system, heating system, and material of pots. Applications of U. atrum suspensions were carried out at 4-week intervals only twice on young plants or were continued during the wh ole growing season until 4 weeks before plants were marketable. The antagon istic treatments were compared with untreated or water-treated controls and with fungicide applications as applied by growers. After applications of U . atrum at 4-weeks intervals, disease development was significantly reduced in experiments carried out in five different greenhouses. In no case did t reatments with fungicides give better control than U. atrum treatments. Two applications of U. atrum resulted in sufficient control when plants were m arketed within 60 days after the last application. In one greenhouse with a n extremely high disease pressure, neither U. atrum nor fungicide applicati ons controlled leaf rot. In additional experiments, the fate of U. atrum co nidia on leaves of cyclamen grown in a system with top-irrigation three tim es per week was studied during a period of 70 days. The number of conidia p er square centimeter of green leaves declined by 50% during the first 10 da ys of the experiment but remained stable during the following 60 days. The percentage of germinated conidia on green leaves increased during the exper iment to approximately 50%. After additional incubation of leaf samples in moist chambers, more than 75% of the conidia had germinated, indicating tha t viable inoculum was present on leaves during the whole experiment. Artifi cial necrosis of leaves was induced by removing leaves from the plants. U. atrum colonized these leaves and competed successfully with B. cinerea on s uch leaves, even when they had been removed 70 days after the U. atrum appl ication. Our results show that U. atrum has the potential to control leaf r ot of cyclamen under a broad range of commercial growing conditions.