Morphophysiological, Molecular and Phytopathological Characteristics of Colletotrichum siamense, the Causative Agent of Ficus elastica Anthracnose

Abstract

Colletotrichum siamense is an emerging plant pathogen with a broad host range and increasing global prevalence, yet its role in ornamental plant diseases remains underexplored. This study reports the first detailed characterisation of C. siamense associated with anthracnose symptoms on Ficus elastica. The fungus was isolated from symptomatic leaves exhibiting dark, necrotic lesions with yellow halos. Morphophysiological features were consistent with C. siamense and included fast-growing floccose colonies, globose conidiomata, cylindrical conidia, and melanized appressoria. Species identity was confirmed through multilocus sequencing of ITS and β-tubulin (BenA) regions, and phylogenetic analyses clustered the isolate with known C. siamense strains from diverse hosts. Additionally, physiological assays revealed enzymatic activity for amylase, hemicellulases, and laccases, whereas the activity of cellulases was absent. Finally, pathogenicity trials on healthy F. elastica leaves fulfilled Koch's postulates, with symptomatic lesions and successful re-isolation of the pathogen. An NCBI database search retrieved over 38,000 C. siamense sequences, with only two associated with F. elastica, underscoring the rarity of reported infections in this host. This study not only expands the known host range of C. siamense but also highlights its pathogenic potential in indoor ornamental settings. These findings emphasise the importance of accurate pathogen identification using a polyphasic approach and underscore the need for phytosanitary vigilance to manage emerging threats to ornamental horticulture.