Necrotic grapevine material from the current season is a source of Botrytis cinerea inoculum

Botrytis cinerea is a pathogen of grapes and other fruit crops which has a complex disease cycle that allows it to survive and infect host tissues through multiple pathways. This study in three vineyards and across three growing seasons investigated the different types of necrotic trash within grape bunches and their potential to act as inoculum sources to cause bunch rot. The amounts and types of bunch trash differed across a growing season, with calyptrae and stamens reducing after pre-bunch closure, while aborted and damaged berries increased towards véraison and harvest. Overall, damaged berries, leaf fragments and tendrils presented the greatest potential as inoculum sources because they had greatest levels of natural infection after véraison and the greatest sporulation potential. The numbers of conidia produced per mm2 of tissue were 2,996, 986 and 2,011 for damaged berries, leaf fragments, and tendrils. However, only aborted berries were consistently associated with development of eventual bunch rot in the three vineyards. The sources of inoculum identified in this study could initiate secondary cycles of infection and sporulation, with consequential bunch rot under moist conditions.