First report of foliar anthracnose on Hydrangea macrophylla, an ornamental plant in Sri Lanka

Foliar anthracnose is a fungal disease that affects the foliage of a wide range of plants under warm and humid conditions. In 2023, Hydrangea macrophylla plants showing brown necrotic lesions on both young and mature leaves were observed in Nuwara Eliya, Central Province, Sri Lanka. Therefore, this study aimed to identify the pathogen causing anthracnose on H. macrophylla leaves using morphological and molecular approaches. The pathogen was isolated on potato dextrose agar (PDA) and cultured at 25 °C in the dark for 7 days. Fifteen isolates with similar morphological characteristics were obtained from five diseased samples collected from different locations within the study area. The upper surface of the fungal colonies appeared white to pale grey, while the lower surface showed concentric pale grey to orange rings. Conidia were aseptate, cylindrical, hyaline, and obtuse at both ends, with an average length of 11.9 μm and width of 2.1 μm (n = 60). Among the fifteen isolates, four randomly selected isolates were used for molecular characterization. Genomic DNA was extracted using a modified protocol of the Promega DNA extraction kit. PCR amplification was performed using internal transcribed spacer primers (ITS1/ITS4), ACTIN primers (Act512F/Act783R), and Histone primers (CYLH3F/CYLH3R). The PCR products were sequenced and compared with related sequences available in GenBank (NCBI). Based on morphological characteristics and sequence analysis, the pathogen was identified as Colletotrichum gloeosporioides. To our knowledge, this is the first report of foliar anthracnose of H. macrophylla caused by C. gloeosporioides in Sri Lanka.