Isolation and identification of Diaporthe phoenicicola causing leaf spot on Rosa roxburghii in China

Rosa roxburghii Tratt is commonly found growing wild in the south China. In recent years, it has been extensively cultivated in Guizhou, Sichuan, and Chongqing. The fruit of Rosa roxburghii Tratt serves as a valuable resource for both medicinal and culinary purposes, with a long-standing history of use in China. Recently, a new leaf spot was found in the field survey of R. roxburghii in Guizhou Province. The pathogens were isolated and identified by conventional isolation methods, and three genes internal transcriptional spacer (ITS), β-microtubulin (TUB2) and translation elongation factor 1-a (EF1-a) were analyzed. Based on morphological characteristics and phylogenetic analyses, the pathogenic fungus was identified as Diaporthe phoenicicola . Pathogenicity test was confirmed by inoculating R. roxburghii cultivars under greenhouse conditions. All R. roxburghii plants inoculated with D.phoenicicola developed symptoms identical to those observed on naturally infected plants in the field. The fungus were reisolated from the diseased leaves and identified as D.phoenicicola based on its morphological and molecular characteristics, confirming Koch's postulates. To our knowledge, this is the first report of R . roxburghii leaf spot disease caused by D.phoenicicola in China. After being infected by leaf spot disease, the R. roxburghii will develop brown or black spots, which may weaken photosynthesis , cause premature leaf senescence and shedding, and reduce the plant's stress resistance. Therefore, this disease may become a threat to R . roxburghii production in China. • First Report of Diaporthe phoenicicola on Rosa roxburghii in China: This study is the first to identify Diaporthe phoenicicola as the causative agent of leaf spot disease on Rosa roxburghii in China, highlighting a new threat to this economically important plant. • Comprehensive Pathogen Identification: The pathogen was identified using both morphological characteristics and molecular phylogenetic analysis of three gene regions (ITS, TUB2, and EF1-α), ensuring accurate species identification. • Pathogenicity Confirmed: Pathogenicity tests confirmed that D . phoenicicola can infect R. roxburghii leaves, causing symptoms identical to those observed in the field, fulfilling Koch's postulates. • Economic and Ecological Impact: The disease can lead to reduced photosynthesis, premature leaf senescence, and decreased stress resistance in R. roxburghi i, potentially impacting both its medicinal and ornamental value. • Potential for Disease Management: This research provides a foundation for developing strategies to manage and control D. phoenicicola infections in R . roxburghii cultivation.