The Influence of Berry Contact within Grape Clusters on the Development of Botrytis cinerea and Epicuticular Wax

Abstract

Mature berries of Thompson Seedless grapes which exhibited flattened surfaces due to contact with other berries during growth were chosen for study. The contact and non-contact surfaces were compared with respect to their epicuticular wax and susceptibility to infection by Botrytis cinerea. When the berries were stained with methylene blue, the flattened surfaces were stained in a greater proportion than could be explained by chanće alone. Scanning electron microscopy showed that the epicuticular wax on the contact surfaces of the berries was mostly amorphous with numerous shallow depressions, as compared to the non-contact surfaces which had well-defined platelets. When the non-contact and contact surfaces of a berry were inoculated with conidia of B. cinerea, the contact surface had a higher proportion of infection than would be expected due to chance alone. Susceptibility to infection was also increased when the epicuticular wax was removed by dipping the berries in chloroform before inoculation.