First report of potential multiple fungicide resistant Botrytis cinerea in South African blueberry orchards

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Abstract The South African blueberry industry has grown consistently over the past few years due to an increase in local and international demand. Like many other crops, blueberries are susceptible to grey mould caused by Botrytis cinerea, resulting in significant reductions in yield. In this study, Botrytis isolates were recovered from symptomatic blueberry fruit, flowers, leaves and undifferentiated buds, but were not found as endophytes in healthy tissues. Phylogenetic analysis of the concatenated glyceraldehyde-3-phosate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60), DNA-dependent RNA polymerase subunit II (RPB2) genes identified 88 isolates as B. cinerea strains, as well as a single B. pelargonii strain. The efficacies of six commercial fungicides with active ingredients potassium bicarbonate, pyraclostrobin & boscalid, fenhexamid, pyrimethanil, fluopyram and cyprodinil & fludioxonil were assessed on detached blueberries that had been infected with a panel of B. cinerea isolates. Only the formulation containing cyprodinil and fludioxonil exhibited complete inhibition of grey mould decay, while some level of resistance to the other six active ingredients may be inherent in the tested isolates. The results presented in this study are the first to contribute towards the characterisation of B. cinerea populations in South African blueberry orchards and provide information regarding fungicide efficacy that can be incorporated into grey mould management strategies.

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