Epidemiology of Botrytis spotting on gerbera and rose flowers grown under glass

Experiments described in this thesis were performed to improve the knowledge on the epidemiology of Botrytis cinerea in glasshouses, with gerbera and rose as model systems. B. cinerea is an airborne fungus, with conidia as the most important propagules in glasshouses. Conidia of B. cinerea are always present in glasshouse air, day and night, troughout the year. The numbers of conidia present in the glasshouse air depend mainly on the production system, wet or dry production system, amount of senescing plant material on the ground, periods with windows open for ventilation. The horizontal and vertical distribution of conidia in glasshouses is fairly uniform, irrespective of the crop. Deposition of conidia on cut flowers takes place in the glasshouse during the production stage. Sedimentation by gravity is a major mechanism. The shape of the flower is one of the factors that affect the number of conidia deposited on the flower surface. Temperature has an effect both on the susceptibility of flowers to B. cinerea and the infectivity of conidia of B. cinerea, whereas relative humidity and radiation only have an effect on the infectivity of conidia. No clear relation between season and susceptibility of flowers to B. cinerea was found. Cuticle and wax on flowers do not seem to be important factors for the susceptibility of flowers to B. cinerea. These epidemiological studies lead to a warning system against B. cinerea damage in the post-harvest stage. If the daily mean relative humidity in the glasshouse for days 6, 7 and 8 before the day of the flower harvest exceeds 70% and the daily mean global radiation outside the glasshouse for days 1, 2 and 3 before the harvest day is below 1500 Jcm -2day -1, there is great risk of B.cinerea damage on cut flowers in the post-harvest stage