Molecular, morphophysiological, and pathogenic characterization of Colletotrichum isolates from strawberry plants in Santa Catarina, Brazil

Strawberry (Fragaria × ananassa) holds significant importance within the small fruits group of temperate climates. However, its high susceptibility to diseases, particularly anthracnose caused by Colletotrichum isolates, can severely limit production. This study aimed to identify and characterize Colletotrichum species causing strawberry anthracnose in Santa Catarina state, Brazil. Isolates were collected from strawberry plants exhibiting typical anthracnose symptoms on different plant parts, in both organic and conventional fields. A phylogenetic analysis was conducted using six loci, including actin (ACT), β-tubulin (TUB2), calmodulin (CAL), glyceraldehyde-3-phosphate-dehydrogenase (GAPDH), glutamine synthetase (GS), and nuclear ribosomal internal transcribed spacer (ITS), to identify the Colletotrichum isolates. Morphological and cultural characteristics, including conidia size, shape, and sexual reproductive structures were assessed. Pathogenicity tests were performed on detached leaves, fruits, and whole plants of the cultivars (cvs.) Albion, Pircinque, and San Andreas. Additionally, lipolytic, lipase, and cutinase activities were evaluated. The multilocus phylogenetic analysis identified the isolates as Colletotrichum nymphaeae, Colletotrichum siamense, and Colletotrichum karstii. Six groups of colony color were observed. Colletotrichum siamense and C. karstii predominantly exhibited cylindrical conidia shapes, while most C. nymphaeae isolates were fusiform. Furthermore, the presence of sexual structures, such as asci and ascospores, was exclusively noted in C. karstii. Pathogenicity tests on leaves and fruits showed that all isolates caused leaf spots and fruit rot in the three tested cvs., except for two isolates of C. nymphaeae (M135 and M165), which did not cause leaf spots on the adaxial leaf surface of cultivar (cv.) San Andreas. Whole plant assays indicated that the isolates caused anthracnose symptoms on leaves, petioles, fruits, flowers, and crowns, with the most prominent symptoms on petioles and fruits. Colletotrichum karstii showed a three-fold higher halo diameter (10.2 mm), indicating increased lipolytic activity, while C. nymphaeae (M133) exhibited a twelve-fold higher lipase activity, and C. siamense had a twenty-eight-fold higher cutinase activity compared to controls. These findings provide new insights into the distribution and pathogenicity of Colletotrichum species causing strawberry anthracnose in Santa Catarina. The molecular, morphological, and enzymatic characterizations enhance our understanding of species-specific virulence factors, which can support the development of targeted disease management strategies for strawberry production.