Stagonosporopsis citrulli: the causal agent of gummy stem blight on Luffa acutangula and Momordica charantia in Guangdong province of China

Luffa acutangula and Momordica charantia, known for their edible and medicinal value, are economically important cucurbitaceous vegetable crops cultivated globally. Gummy stem blight, primarily caused by Stagonosporopsis species, is a devastating disease on cucurbits, resulting in significant economic losses. Although occurrence of gummy stem blight on L. acutangula and M. charantia has been reported previously, the pathogen responsible for the disease on these two crops has not been clearly identified due to the taxonomical nomenclature changes. During the period from 2018 to 2024, diseases resembling gummy stem blight were commonly observed on L. acutangula and M. charantia in Guangdong province of China, with the disease incidence for L. acutangula as 13.5%-21.7% in Guangzhou and 13.5%-25.0% in Huizhou and the disease incidence for M. charantia as 20.0%-30.0% in Guangzhou and 16.7%-26.7% in Huizhou. Samples of symptomatic leaves, stems, and fruits were collected, and 52 fungal isolates with similar colony morphology were obtained. The initial identification of these isolates was based on cultural and morphological characteristics, which placed them in Stagonosporopsis. Subsequently, they were identified as S. citrulli with multilocus phylogenetic analyses using the ribosomal DNA internal transcribed spacer, and portions of β-tubulin, chitin synthase I, and calmodulin genes. Pathogenicity tests were conducted on leaves and fruits of L. acutangula, M. charantia, and Cucumis sativus with representative isolates of S. citrulli. These isolates produced lesion symptoms on L. acutangula and M. charantia similar to the disease symptoms in the field. Furthermore, they were also pathogenic to C. sativus. The same pathogen was re-isolated from lesions of inoculated plants to fulfill Koch’s postulates. To our knowledge, this study is the first report about identification of S. citrulli as the causal agent of gummy stem blight on L. acutangula and M. charantia in China.