Benzimidazole-resistant strains isolated from anthracnose-affected leaves of Japanese pear were not negatively correlated with cross-resistance to diethofencarb. Based on this, the strains were thought to perhaps be Colletotrichum acutatum, which is inherently insensitive to both benzimidazoles and diethofencarb. However, morphological studies and polymerase chain reaction using primers that specifically amplified the internal transcribed spacer 1 region of ribosomal DNA of C. gloeosporioides and C. acutatum, showed that the strains were intermediately benzimidazole-resistant of C. gloeosporioides. EC50 of benomyl for mycelial growth of the strains was around 15 ppm, an intermediate value between that for sensitive strains and highly resistant strains. The deduced amino acid at codon 200 was altered from phenylalanine (TTC) to tyrosine (TAC), based on sequence analysis for the β-tubulin gene. Control efficacy of benomyl against intermediately benzimidazole-resistant strains was low in inoculation tests.
