Negatively correlated cross-resistance to diethofencarb funcigide in benomyl-resistant Botrytis cinerea of grapes

Mario Alvarez A.1

Benzimidazole-resistant field isolates of Bottytis cinerea from grapes showed an increased sensitivity to diethofencarb on nutrient media as compared with the wild-type sensitive isolates. Diethofencarb was highly effective to inhibit the benzimidazole resistant strains but almost non-fungitoxic to the sensitive strains, showing a negatively correlated cross-resistance to benomyl. The ED50 values of diethofencarb in inhibiting radial mycelial growth of resistant and sensitive strains were 0.05 and 416.87 ppm, respectively, while the ED50 values of benomyl against these strains were 732.80 ppm and 0.11 ppm, respectively, and the ED50 values of the mixture diethofencarb + carbendazim were 0.07 ppm and 0.10 ppm, respectively. Benzimidazole-resistant and -sensitive isolates were inoculated on bean plantas, previously sprayed with fungicides. Resistant isolates caused complete infection on benomyl-treated leaves, but no infection ocurred on diethofencarb- or iprodione-treated leaves. Sensitive isolates caused no infection on benomyl- or iprodione- treated leaves, but fully infected leaves sprayed with diethofencarb. Treatment with the commercial mixture of diethofencarb plus carbendazim controlled infection when inoculation was carried out with either resistant or sensitive isolates.

Key words: fungicides, resistance, gray mould.

1 Estación Experimental La Platina (INIA). Casilla 439. Correo 3, Santiago, Chile.

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