Evaluation of Sweetpotato (Ipomoea batatas (L.) Lam.) Genotypes for Resistance to Alternaria Leaf Petiole and Stem Blight (Alternaria spp.) in Uganda

Alternaria leaf petiole and stem blight (Alternaria spp.) is an important sweetpotato (Ipomoea batatas (L.) Lam.) disease in Uganda. Severity of the disease varies with environment, with higher disease levels recorded under high moisture and humidity conditions. To breed for resistance to this disease, germplasm that is resistant must be identified through multi-locational trials. This study was conducted to evaluate selected sweetpotato genotypes for stable resistance to Alternaria blight across sites and seasons. Thirty sweetpotato genotypes from different agro-ecological zones of Uganda and the National Sweetpotato Program were evaluated for resistance to Alternaria blight using fungicide treatment and Alternaria blight pathogen inoculation at Namulonge and Kachwekano over three seasons. There were highly significant differences among the genotypes for Alternaria blight severity with higher disease levels at Kachwekano than Namulonge. Genotypes Shock, Silk Luwero and the resistant check Tanzania had the lowest Alternaria severity and were therefore the most resistant while NASPOT 1 and NASPOT 7 had the highest severity values and were the most susceptible. Improved cultivars were more susceptible than the landraces. Genotypes Tanzania and Namusoga and environment Namulonge 2015B were the most stable for Alternaria blight. Treatment with fungicide resulted in variable reductions in Alternaria blight severity among genotypes across seasons and sites with NASPOT 1 having the lowest percentage reduction of 40.8% between the Alternaria inoculated and fungicide treated plots. Kigaire recorded the highest percentage disease reduction of 63.6%. Those genotypes with acceptable performance for Alternaria blight may be used as parents in breeding new genotypes with improved performance.