Prevalence of Botrytis cinerea in plum and weed tissue: an investigation to elucidate pathogen ecology, for new decay control strategies

Botrytis cinerea, the cause of grey mould decay in plums, is of commercial importance in the South African export fruit industry. Despite various efforts, decay control failures, leading to financial forfeitures to producers, continue to occur. Such failure to control decay may imply that knowledge of the ecology of the fungus is incomplete. The aim of this study was to investigate the prevalence of B. cinerea in both pre- and postharvest plum tissue, as well as in weeds, over the plum production season. The occurrence B. cinerea in different tissue types may give insight into the ecology of the fungus. This, in turn, could reveal critical points for decay control. An orchard with a high incidence of Botrytis grey mould, and high weed infestation, was identified. Samples of blossoms, fruit at harvest and fruit during and after storage were evaluated for the presence and quantity of B. cinerea DNA, using molecular techniques. Weeds were also screened for the presence of B. cinerea. Results indicated that B. cinerea was omnipresent in blossoms. In fruit, despite fungicide applications, both B. cinerea DNA and fruit decay increased in a linear relationship as storage time progressed. Notably, the amount of B. cinerea DNA in blossoms and fruit also revealed positive correlations to percentage fruit decay. Additionally, most weeds tested positive for the presence of B. cinerea. However, Potato Dextrose Agar isolations from fruit or weed tissue failed to successfully isolate B. cinerea. From this study, it was clear that B. cinerea ecology in plums could be more complicated than generally held. Alternative grey mould decay control strategies should be considered, potentially with a stronger focus on fungicide protection of blossoms from primary infection and eradication of weeds, which act as bridging hosts for the fungus to survive and ultimately lead to subsequent fruit infections.