Molecular Identification and Pathogenicity of Neocosmospora solani Causing Dry Rot on Potato Tubers

Abstract

Dry rot symptoms observed on stored potato (Solanum tuberosum L.) tubers were investigated to identify the causal pathogen and characterize its molecular identity and pathogenic potential. Infected tubers collected from storage facilities exhibited sunken lesions, internal browning, wrinkling of tuber tissues, and progressive decay under warm and low-humidity storage conditions. Fungal isolates obtained from symptomatic tissues produced fast-growing, cottony colonies with white to cream mycelium that later turned pale to dark brown on potato dextrose agar. Microscopic examination revealed septate hyphae and abundant microconidia and macroconidia consistent with members of the Neocosmospora solani complex. Pathogenicity assays conducted on healthy potato tubers under controlled storage conditions successfully reproduced dry rot symptoms, confirming virulence and fulfilling Koch’s postulates. Molecular identification using ITS rDNA and translation elongation factor 1-alpha (TEF1-α) gene sequencing confirmed the isolates as Neocosmospora solani, showing high similarity with reference sequences from global databases. Phylogenetic analysis placed all isolates within a well-supported N. solani clade, indicating limited intraspecific variation among populations from different storage environments. Observed minor sequence differences suggested possible adaptation to local storage conditions and substrate variability. Disease development was strongly associated with mechanical injuries, poor curing practices, and elevated storage temperatures, which facilitated pathogen entry and colonization. The study highlights the significance of N. solani as a major post-harvest pathogen of potato tubers and emphasizes the need for improved storage hygiene and handling practices. Integrated management strategies, including careful harvesting, proper curing, and controlled storage conditions, are recommended to reduce dry rot incidence and post-harvest losses.