Blossom–end Rot of Pears: Systemic Infection of Flowers and Immature Fruit by Botrytis cinerea 1

A histological study was made of the systemic growth of Botrytis cinerea from styles, stamens and sepals to the flower receptacle and mesocarp of immature pear fruit. In most styles, hyphal growth ceased in the upper portion at the onset of stylar senescence, which occurred at about 1 wk after full bloom. Hyphae never passed through styles into the carpel. Unlike the styles, hyphae in filaments grew without restriction and progressed within 4 days, via vascular tissue, through sepals into tissues of the upper end of the flower receptacle, or of the mesocarp adjoining the sepals, without causing symptoms. Filaments remained green to partly green until harvest. B. cinerea entered filaments and spread into the receptacle or mesocarp at any time between blossoming and harvest and then became latent in these tissues. Filaments were, however, more susceptible at the flowering stage. After 2 months floral tubes were closed, and the stamens protected from infection. Careful inspection of ripe, cold–stored fruit showed that decay invariably spreads from mesocarp tissue adjoining the sepals, outward along the vascular bundles, but not from secondary inoculum in the floral tube. The behaviour of the pathogen suggests that control of blossom–end rot could be achieved if pears are sprayed with fungicide at 75—100% petal fall (when most stamens are exposed) and a month later (before floral tubes started to close).