Characterization and pathogenicity of Fusarium solani causing foot rot on hemp (Cannabis sativa L.) in Southern Italy

Symptoms of foot rot were observed on hemp (Cannabis sativa) plants in Campania region (Southern Italy) in 2018. The symptoms consisted of brownish areas along the main stem followed by wilting and dropping of leaves. The bark was easily removed in correspondence of the lesions since the inner part of the cortex was affected too. The causal agent was isolated on potato dextrose agar and stored at the Research Centre for Cereal and Industrial Crops of Caserta. On carnation leaf agar, the fungus produced long monophialidic conidiogenous cells and both micro- and macroconidia. The first were oval, ellipsoid and fusiform prevalently 0- and 1-septate with length 9.84–12.68 μm and width 2.61–4.15 μm, while falciform macroconidia were prevalently 3- and 4-septate with length and width 23.87–29.23 × 3.22–4.98, respectively. Chlamydospores were observed intercalated in the hyphae, globose to oval in shape with smooth or rough wall, 5–15 μm in diameter. Morphologically, the fungus was identified as Fusarium solani, which was also supported by the BLASTn and the phylogenetic analysis of the sequences of the internal transcribed spacer and elongation factor 1-α genes. Koch’s postulates confirmed F. solani as the etiological agent of the observed disease. Cluster analysis applied to the two genes demonstrated that our isolates belong to the clade 3 of the F. solani species complex.