Identification of Exserohilum rostratum causing leaf spot on Dendrobium amabile and Dendrobium clavatum
Fungal diseases are among the most persistent and underestimated threats to orchid cultivation, often causing severe decline if not detected early. In this study, leaf spot disease was recorded on two native orchid species, Dendrobium amabile and D. clavatum. To identify the causal agent, symptomatic leaves were collected and subjected to fungal isolation, pathogenicity testing, morphological characterization, and multi‑locus sequence analysis. Artificial inoculation reproduced typical leaf spot symptoms, confirming pathogenicity. Morphological traits of colonies and conidia indicated affiliation with the genus Exserohilum. Molecular analyses of the ITS, LSU, TEF1, and ACT gene regions further resolved the isolates as E. rostratum, with high sequence similarity among the representative strains. Minor morphological variation was noted, particularly in conidial dimensions, but overall consistency supported species‑level identification. This study establishes a new host association between E. rostratum and D. amabile and D. clavatum and demonstrates the effectiveness of combining morphological and molecular approaches for precise fungal identification. The generated multilocus dataset provides a useful reference for future studies on orchid pathogens and fungal taxonomy.