Diversity, pathogenicity, and mycotoxin profiling of Alternaria species infecting potato in India

Alternaria species are the major pathogens affecting potatoes, yet their pathogenic variability among species and potential to cause disease due to mycotoxins production are not well understood. A total of 48 symptomatic samples (44 leaves and 4 tubers) were collected from potato fields across major cultivation regions of India. From these, 25 representative isolates were selected to represent the full range of pathogenicity (low, moderate, and high virulence) for detailed molecular, morphological, and toxigenic characterization. Morphologically different strains were further subjected to ITS-based phylogenetic analysis, which clustered the isolates into section Alternaria and section Porri. HPLC analysis quantified mycotoxins production in all isolates with tenuazonic acid (TeA) ranging from 30.00-417.81 µg/mL and alternariol (AOH) from 20.00-97.01 µg/mL. LC-MS/MS with multiple reaction monitoring (MRM) transitions confirmed both compounds in representative isolates. Plate assay of cell wall-degrading enzyme activities indicated that isolates with higher pathogenicity had larger halo diameters, implying higher cellulase and pectinase activity. Hierarchical cluster analysis differentiated isolates based on enzymatic and toxigenic profiles, while correlation analysis showed a high positive correlation between cellulase and pectinase activity (r = 0.62) and moderate correlations between enzyme activity and toxin production (r = 0.48-0.51). These results point towards a synergistic interaction of enzymes and mycotoxins in Alternaria spp. pathogenicity of potato plants. This presents a comprehensive virulence profiling of Alternaria spp. infecting potato plants in India revealed the occurrence of highly virulent Alternaria isolates and highlights the need to monitor newly emerging Alternaria species with high virulence potential in potato production systems.