Morphological, molecular, and pathogenic characterization of Colletotrichum isolates associated with apple anthracnose in tropical highland orchards of Indonesia

Apple anthracnose caused by Colletotrichum spp. is an important disease affecting tropical highland apple production in Indonesia. This study characterized Colletotrichum isolates associated with apple anthracnose based on morphology, pathogenicity, and ITS-based molecular analysis. Symptomatic apple fruits were collected from four major apple-producing areas in East Java, Indonesia. Isolates were evaluated for colony morphology, radial growth, microscopic characteristics, and pathogenicity using wounded and non-wounded inoculation methods on apple fruits at different developmental stages. Morphological observations revealed variation in colony pigmentation, mycelial growth, and conidial morphology among isolates. ITS sequence analysis showed high similarity (99.48–100%) to taxa within the genus Colletotrichum, including isolates closely related to C. gloeosporioides, C. siamense, C. nymphaeae, and C. aenigma. Pathogenicity assays confirmed that all isolates caused anthracnose symptoms, with lesion development varying among isolates and fruit developmental stages under both wounded and non-wounded conditions. Young, intermediate, and mature fruits, corresponding to 1, 2.5, and 4 months after fruit set, respectively, showed differential responses, with intermediate-stage fruits exhibiting greater lesion development under wounded conditions. These findings demonstrate considerable variability among Colletotrichum isolates and support improved diagnosis and disease management strategies in tropical apple production systems.