Pathogenicity and Virulence of Alternaria Blight Isolates on Three Selected Cultivars of Sweetpotato in Uganda

Abstract

Alternaria species cause diseases to more than 380 host plants with the damage causing 60%-100% plant death. This makes it a species of interest for sweetpotato researchers and farmers. However, there is a shortage of information since limited research has been conducted on Alternaria species that causes Alternaria blight of sweetpotato. This study aimed to fill this research gap. A study was carried out on the Alternaria blight disease of sweetpotato. Alternaria bataticola and Alternaria alternata were isolated from the diseased sweetpotato stems, vines, and leaves. From the cultures, Alternaria bataticola was the most frequently isolated species from the infected plants, glaringly higher in frequency than Alternaria Alternaria. Specifically, pathogenicity tests were conducted on six representative isolates tested on three selected varieties in the study. The pathogenicity tests on the susceptible sweetpotato variety using all six fungal isolates showed that only Alternaria bataticola was more aggressive producing symptoms of larger lesions that are dark grey in color, it produces characteristic symptoms of black lesions on the leaf abaxial, nodes, and on the stems. The observation of the characteristic symptom of dark grey lesions with concentric rings on the leaves and re-isolation of the pathogen from infected leaves and stems confirmed that both Alternaria bataticola and Alternaria alternata were responsible for the sweetpotato Alternaria blight disease. Isolates, cultivar (isolate × cultivar) interaction, and experimental effects were obtained.