ABSTRACT
Ten experiments in six different commercial greenhouses were conducted to study the effect of spraying conidial suspensions of the saprophytic fungus Ulocladium atrum (1 × 106 conidia per ml) on infection of leaves and flower petioles of cyclamen by Botrytis cinerea (gray mold). The greenhouses represented the range of Dutch growing systems of cyclamen, differing considerably 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 whole growing season until 4 weeks before plants were marketable. The antagonistic 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 treatments with fungicides give better control than U. atrum treatments. Two applications of U. atrum resulted in sufficient control when plants were marketed within 60 days after the last application. In one greenhouse with an extremely high disease pressure, neither U. atrum nor fungicide applications controlled leaf rot. In additional experiments, the fate of U. atrum conidia on leaves of cyclamen grown in a system with top-irrigation three times per week was studied during a period of 70 days. The number of conidia per square centimeter of green leaves declined by 50% during the first 10 days of the experiment but remained stable during the following 60 days. The percentage of germinated conidia on green leaves increased during the experiment to approximately 50%. After additional incubation of leaf samples in moist chambers, more than 75% of the conidia had germinated, indicating that viable inoculum was present on leaves during the whole experiment. Artificial necrosis of leaves was induced by removing leaves from the plants. U. atrum colonized these leaves and competed successfully with B. cinerea on such leaves, even when they had been removed 70 days after the U. atrum application. Our results show that U. atrum has the potential to control leaf rot of cyclamen under a broad range of commercial growing conditions.
