Characterization and Pathogenicity of Pseudopestalotiopsis vietnamensis Causing Gray Blight of Wuyi Rock Tea (Camellia sinensis) in China and Specific Mechanisms of Disease Infection

Gray blight disease (GBD) causes significant losses in tea production in China. Although genes and biological processes involved in resistance to fungal disease in tea plants have been identified, specific mechanisms of the GBD infection process remain unknown. In this study, morphological and multi-gene (TEF-TUB-ITS) phylogenetic characteristics were used to identify isolate CLBB1 of Pseudopestalotiopsis vietnamensis. Pathogenicity tests confirmed that isolate CLBB1 from tea leaves caused GBD in the susceptible tea cultivar Wuyi Rock (Camellia sinensis var. sinensis cv. Shuixian). Spores began to germinate 24 h after infection (hai), and after 48 h, elongated fungal hyphae formed from a single conidium. Transcriptome analysis revealed that 482, 517, and 369 genes were differentially expressed at 24, 48, and 72 hai, respectively, in Wuyi Rock tea leaves. Isolate CLBB1 infection elicited phenotype-related responses and activated defense-related pathways, including plant-pathogen interaction, MAPK signaling, and plant hormone signal transduction, suggesting a possible mechanism underlying phenotype-based susceptibility to CLBB1. Thus, a new Ps. vietnamensis strain causing GBD in the tea cultivar 'Shuixian' was discovered in this study. Transcriptome analysis indicated that pathogen invasion activated chitin-related MAPK pathways and that tea plants required a hormone to restrict CLBB1.