Occurrence of strobilurin-resistant strains of Colletotrichum gloeosporioides, the causal fungus of mango anthracnose.

Sensitivity to strobilurin fungicides was tested for 107 isolates of Colletotrichum gloeosporioides, obtained in 2009 and 2010 from mangoes with anthracnose in Okinawa Prefecture, Japan. When isolates were grown on potato dextrose agar containing 1000 ppm of salicylhydroxamic acid and various concentrations of azoxystrobin and kresoxim-methyl, two strains showed a minimal inhibitory concentration of >3000 ppm and were regarded as resistant. The control efficacy of azoxystrobin against two strains was low in a leaf bioassay, and the G143A point mutation in the cytochrome b gene, conferring resistance to strobilurins, was confirmed by PCR-RFLP using restriction enzyme Fnu4HI.