Mycological Studies and Pathogenicity of Tannia (Xanthosoma sagittifolium) Postharvest Tuber Rot

Pathogenicity assays were conducted in 2021 and repeated in 2023 at the National Root Crops Research Institute (NRCRI), Umudike, Nigeria, to identify the primary aetiology of postharvest deterioration in decaying Xanthosoma sagittifolium (tannia) tubers. Among the fungal isolates recovered, Penicillium spp. demonstrated the highest virulence, characterized by aggressive growth patterns and significant rot progression (27 mm). Rot initiation commenced upon mycelial contact of pathogens with tuber surface wounds, triggering a sequence of events. Upon contact, these fungi produced large quantities of oxalic acid and polygalacturonases, which acted synergistically. Oxalic acid sequestered calcium, lowering the pH to optimize endopolygalacturonase and cellulase activity. The advancing hyphae depleted pectic substances within tuber tissues, leading to peroxidase release via enzymatic activity. This sequential breakdown ultimately results in watersoaked, necrotic, and macerated tuber tissues.