Identification of Nigrospora sphaerica and Curvularia lunata as causal agents of leaf spot disease in cantaloupe (Cucumis melo L.) in Southern Vietnam

Abstract

Leaf spot disease poses a significant threat to cantaloupe (Cucumis melo L.) production in Vietnam due to its detrimental impact on yield, fruit quality, and economic profitability. Despite its importance, the causal agents and epidemiological patterns of the disease remain poorly understood. This study investigated the prevalence of leaf spot disease in three major cantaloup-growing regions in southern Vietnam, including Binh Duong, Tay Ninh, and Ho Chi Minh City, and further identified the responsible pathogens. Disease monitoring revealed that disease incidence (DI) ranged from 15 to 22% during fruit maturation at 50 days after planting. Additionally, the disease severity index (DSI) varied from 6.33 to 11.89, highlighting the necessity of pathogen identification to develop effective disease management strategies. Through morphological characterization, molecular analysis of ITS, tub, and TEF1α gene regions, and pathogenicity tests following Koch’s postulates, two fungal pathogens were identified: Nigrospora sphaerica (N1) and Curvularia lunata (N2). Pathogenicity studies confirmed their high virulence, with both pathogens causing significant disease symptoms by 11 days post-inoculation, consistent with Koch’s postulates. This study represents the first report of these pathogens causing leaf spot disease in cantaloupe in Vietnam, providing crucial insights for developing effective disease management strategies in the region.