Isolation and identification of pathogen causing anthracnose on Anoectochilus roxburghii and its sensitivity to nine fungicides

In this study, the causative pathogen of anthracnose on Anoectochilus roxburghii was classified. According to Koch's law, tissue separation method was used to isolate the pathogen from the diseased leaves. The pathogenic fungus was identified based on the morphologic characteristics and multi-locus phylogenetic analysis by combing five genes, including actin ACT, β₂-tubulin gene TUB₂, chitin synthase A gene CHS-I, glyceraldehyde-3-phosphate dehydrogenase gene GAPDH, and ribosome internal transcription spacer ITS. And the in vitro inhibitory activities of nine common fungicides against this pathogen were determined to provide a basis for its control. In the pathogenicity tests, the isolates caused similar symptoms as the natural symptom in the fields, indicating they were the pathogenic fungi. According to the colony, conidial and appressorium morphology of pathogenic fungi, it was preliminarily judged as Colletotrichum gigasporum. The molecular identification based on the phylogenetic analysis of ACT, CHS-I, GAPDH, ITS and TUB₂ was consistent with the morphological identification. Thus, the pathogen causing the anthracnose disease on A. roxburghii was identified to be C. gigasporum. The results of the in vitro fungicidal activity showed that the EC₅₀ values of prochloraz, tebuconazole, trifloxystrobin, Y13149, difenoconazole, prothioconazole, fluazinam, thiophanate-methyl and chlorothalonil against C. gigasporum were 0.0145, 0.240, 18.2, 29.9, 0.114, 0.402, 0.0191, 2.80, and 38.5 μg/mL, respectively. Among them, prochloraz and fluazinam had the strongest fungicidal activities.