Production and viability of sclerotia from fungicide‐resistant and fungicide‐sensitive isolates of Botrytis cinerea, B. elliptica and B, tulipae

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Abstract
Production of sclerotia by isolates of three Botrytis spp. differing in resistance to benzimidazole and dicarboximide fungicides was compared in vitro. Sensitive isolates of B. cinerea and B. tulipae produced fewer sclerotia than benzimidazole‐resistant isolates, but there were no differences in the size of sclerotia within each species. For B. elliptica, sclerotia of dicarboximide‐resistant isolates were larger and less numerous than those of sensitive isolates. Sclerotia from fungicide‐resistant and ‐sensitive isolates of B. elliptica. B. tulipae and B. cinerea were produced in vitro, placed in nylon bags, set in loam soil at soil depths of 0, 10 and 20 cm, and recovered periodically after 1‐18 months. Sclerotial viability declined during the 18 months, and was lowest at the soil surface for sclerotia of B. cinerea and B. tulipae. For B. elliptica, sclerotial viability of fungicide‐sensitive isolates was reduced to 50% after 18 months, compared to 21 % for dicarboximide‐resistant isolates, when averaged over all depths. Sensitive isolates of B. tulipae maintained a trend of higher viability than benzimidazole‐resistant ones, and fungicide‐sensitive isolates showed greater viability at 18 months (49%) than did benzimidazole‐resistant ones (27%). No differences in sclerotial viability were apparent between the fungicide‐resistant and ‐sensitive isolates of B. cinerea, with an average viability of 77% after 18 months. After 18 months of field exposure, all isolates retained their original fungicide‐resistance groupings, indicating the persistence of fungicide resistance in sclerotia.

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