<i>Stagonosporopsis citrulli</i> : The Causal Agent of Gummy Stem Blight on <i>Luffa acutangula</i> and <i>Momordica charantia</i> in Guangdong Province of China

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