Stem canker of dragon fruit (Hylocereus polyrhizus): Neocytalidium sp. is the new cause of the disease and its control using the sodium salt

This study aimed to isolate and characterise a fungal pathogen associated with stem canker on dragon fruit and to evaluate the efficacy of sodium salt as an alternative control against it. The fungal pathogen was isolated and identified by morphological and cultural methods. SMNND11 and ARPN11 isolates, which are morphologically alike Neoscytalidium sp., were selected for the present study. The colony's mycelial mass was greyish-white and turned to dark greenish-grey. The shape of the arthroconidia was ellipsoid to ovoid and hyaline to dark brown with septate arthrospores. The hyphae were brown in colour, septate, branched and constricted into spore chains before disarticulation. Based on the blast analysis using the aligned sequences of the internal transcribed spacer, the SMNND11 isolate was highly genetically identical (100%) to Neoscytalidium dimidiatum, the ARPN10 isolate was 98.6% identical to Neoscytalidium sp. and the neighbour-joining analysis revealed that both isolates were grouped into the same genus, Neoscytalidium sp. The in vitro study revealed that sodium salt at a concentration of > 3% showed high potential in suppressing the mycelial growth of the SMNND11 isolates. In a field trial, a sodium salt solution at 30 g/L applied twice a week, along with rotating chemical fungicides applied once a week, were able to reduce the disease severity of the stem canker disease on the dragon fruit. This study revealed that Neoscytalidium sp., as well as N. dimidiatum, is the positive pathogen that infects dragon fruit plants in IP2TP Sumani and Aripan West Sumatra. Thus, the culture and field studies support the potential control technique to alternating chemical fungicide on dragon fruit.