INFLUENCE OF ENVIRONMENTAL-CONDITIONS ON DISPERSAL OF BOTRYTIS-CINEREA CONIDIA AND ON POSTHARVEST INFECTION OF GERBERA FLOWERS GROWN UNDER GLASS

Dispersal of Botrytis cinerea in a gerbera crop grown in two glasshouses 30 km apart was studied over a period of 18 months, in 1988 and 1989. Conidia were caught in spore traps consisting of agar in petri dishes exposed at different heights in the crop in each glasshouse. No seasonal patterns could be identified in the spore catches, assessed as colonies on the agar traps after incubation. The number of lesions caused by conidial infection of gerbera flowers following incubation, however, showed a distinct pattern. In spring and early summer few lesions were recorded whereas at other times of the year many lesions appeared. In linear regression analysis, variation in numbers of colonies (spore catches could not be explained by environmental factors recorded during the experiments. Linear regression accounted for 77% and 81% of the variation in the number of lesions on flowers in the two glasshouses, in terms of relative humidity (positively correlated), global radiation outside the glasshouse (negatively correlated) and age of the crop (positively correlated). Despite differences in the systems by which the gerbera crop was produced and in the spore catches, the numbers of lesions on gerbera flowers in the two glasshouses were significantly correlated though not significantly different from each other.