Evaluation of the incidence of the G143A mutation and cytb intron presence in the cytochrome bc-1 gene conferring QoI resistance in Botrytis cinerea populations from several hosts.

BACKGROUND: Previous studies have shown that resistance of Botrytis cinerea to QoI fungicides has been attributed to the G143A mutation in the cytochrome b (cytb) gene, while, in a part of the fungal population, an intron has been detected at codon 143 of the gene, preventing QoI resistance. During 2005-2009, 304 grey mould isolates were collected from strawberry, tomato, grape, kiwifruit, cucumber and apple in Greece and screened for resistance to pyraclostrobin and for the presence of the cytb intron, using a novel real-time TaqMan PCR assay developed in the present study.
RESULTS: QoI-resistant phenotypes existed only within the population collected from strawberries. All resistant isolates possessed the G143A mutation. Differences were observed in the genotypic structure of cytb. Individuals possessing the intron were found at high incidence in apple fruit and greenhouse-grown tomato and cucumber populations, whereas in the strawberry population the intron frequency was lower. Cultivation of QoI-resistant and QoI-sensitive isolates for ten culture cycles on artificial nutrient medium in the presence or absence of fungicide selection showed that QoI resistance was stable.
CONCLUSIONS: The results of the study suggest that a high risk for selection of QoI-resistant strains exists in crops heavily treated with QoIs, in spite of the widespread occurrence of the cytb intron in B. cinerea populations. The developed real-time TaqMan PCR constitutes a powerful tool to streamline detection of the mutation by reducing pre- and post-amplification manipulations, and can be used for rapid screening and quantification of QoI resistance.