Fungal causal agents of the Black Spot of the cactus (Opuntia ficus-indica) in Colima, Mexico

Objective/Background: The prickly pear cactus (Opuntia ficus-indica) holds significant economic, social, and cultural importance in Mexico. However, it is recurrently affected by Black Spot disease (BS), caused by various phytopathogenic fungi. Identifying the causal agents of BS in commercial prickly pear crops is crucial for efficient agronomic management of the disease. The objective of this study was to identify the phytopathogenic fungi responsible for BS in prickly pear plantations in the Colima state, Mexico. Materials and Methods: Fifty cladodes from 50 plants exhibiting BS symptoms were collected from commercial plantations in Colima. The pathogenicity of the isolated fungi was verified using Koch’s postulates, and those causing the most severe BS symptoms were molecularly identified. Results: Thirty-five fungi were isolated from plants with BS symptoms, of which 20 exhibited distinct mycelial growth. Only six fungi induced BS symptoms; three of them were responsible for severe symptoms in cladodes: Alternaria alternata, Corynespora cassiicola, and Neoscytalidium dimidiatum. Conclusion: BS is caused by various phytopathogenic fungi, but this is the first report of C. cassiicola and N. dimidiatum as causal agents of BS in prickly pear cactus.