Assessment of Phoma Blight on Potato (Solanum tuberosum) in Borno State, North East Nigeria

Potato (Solanum tuberosum) cultivation has been identified as a strategic crop for food security diversification in Borno State, particularly in highland areas with suitable temperatures. Phoma blight, caused by Phoma foveata and related species, is a soilborne disease complex associated with seedpiece decay, stolon canker, and foliar blight, potentially causing substantial losses under wet conditions. This study assessed the incidence of Phoma blight on potato across three district farms in Borno State during the 2023 growing season. Sixty plots were surveyed, with disease ratings applied to seedpiece emergence, foliage, and tuber samples at harvest. Isolation and morphological characterisation confirmed the presence of Phoma foveata alongside Phoma andigena in symptomatic material. Disease incidence based on foliage symptoms averaged 31 percent, while harvest examination revealed skin blemish-related defects in 24 percent of tubers from infected plots. Potato seed sourced from informal local markets showed significantly higher seedpiece decay rates compared to certified seed imported from highland production zones. Management practices observed in the field were largely inadequate, with no growers using certified seed treatments targeting Phoma at the time of planting. The study recommends certification-based seed potato distribution systems for Borno State and evaluation of registered seedpiece treatments effective against Phoma under North East agroecological conditions. Keywords: potato, Phoma blight, seed potato, Borno State, disease assessment.