Colletotrichum karstii: causal agent of anthracnose of Dendrobium nobile in Mexico

The presence of well-defined and depressed circular leaf spots, dark in their core and surrounded by a light brown dim halo, was observed on Dendrobium nobile plants in the municipality of Ixtaczoquitlán, state of Veracruz, Mexico, in 2019. Colletotrichum isolates were consistently obtained from symptomatic plants of D. nobile. The morphological characteristics of these isolates resembled each other, and their pathogenicity could be confirmed based on the necrotic lesions caused by three of these isolates on D. nobile plants 10 days after inoculation. The causal agent of this disease was identified as Colletotrichum karstii, based on morphological characteristics and the partial sequences of the ITS1-5.8S-ITS2, calmodulin and β-tubulin genes of the DNA of three representative isolates (CKFG004, CKFG005 and CKFG006). To our knowledge, this is the first report which identifies C. karstii as the causal agent of anthracnose of D. nobile leaves in Mexico.