The prevalence of Botrytis cinerea in and on plums, and alternative host plant tissue: A preliminary investigation on the occurrence of the fungus pre-and-post harvest in order to elucidate pathogen ecology, for new decay control strategies

Botrytis cinerea causes grey mould decay in plums, which is of commercial importance to the South African stone fruit industry, since efforts to control decay are not always effective, with subsequent financial forfeitures to producers. It is possible that knowledge on some facets of the ecology of the fungus is incomplete which hampers optimal control of the fungus. The aim of this study was to investigate the prevalence of B. cinerea in both pre-and post-harvest plum tissue, as well as in weeds, over the plum production season. The occurrence B. cinerea over time, and in different tissue types in the orchard, may give insight into the ecology of the fungus, which in turn could reveal critical points for decay control.

An orchard with a known high incidence of Botrytis grey mould, and high weed infestation, was identified. For 25 trees, samples of blossoms, mature fruit at harvest, and mature fruit during and after storage was evaluated for the presence and quantity of B. cinerea DNA using quantitative real time polymerase chain reaction (qRT-PCR) technology. Weeds were also screened for the presence of B. cinerea.

• B cinerea was detected in various samples throughout the whole timeline of sampling, which included blossoms, fruit at harvest, and from fruit during/after cold storage.
• Notably the fungus was always present in blossoms in high
• cinerea was detected in more than 14 weed species obtained from the orchard floor, and it was present in weeds both during spring and summer time.
• Potato Dextrose Agar isolations from fruit or weed tissue failed to isolate cinerea.
• Despite the application of a post-harvest fungicide, cinerea DNA levels, as well as fruit decay, increased in a strong linear relationship with storage time. Thus, the longer the storage period, the greater the amount of DNA and decay in fruit.
• The amount of cinerea DNA in fruit also directly correlated to percentage decay.
• Notably, the amount of cinerea DNA in blossoms showed a strong positive correlation (R² = 0.9653) to percentage fruit decay at the end of the storage period.

This preliminary investigation, on the presence of B. cinerea in various host tissues, brought forth previously unknown insights on the pathogen. B. cinerea was frequently found in healthy plum and weed tissues and the strong correlations between levels of B. cinerea DNA in plum tissues with decay in plums were evident. These results urge further exploration into the unknown aspects of the nature of this fungus. An investigation on the role of insects or wind in B. cinerea transfer from weeds to trees in bloom may prove useful in finding weak links in the life or disease cycle which could be targeted for decay control. Possibly, repetitive fungicide applications to blossoms to prevent primary infection early in the growing season and eradication of weeds could contribute to successful decay control. However, confirmation of results in other plum cultivars in various cultivation areas is needed. These results may not be universal to all plums or stone fruit. Should these trends remain, and possibly more new information come to light, it is imperative that appropriate, tested, management strategies be devised for accurate decay control.