Identification of causal agent of gray blight disease in <i>Camellia sinensis</i> and screening of resistance cultivars

Tea gray blight disease represents a major fungal threat to tea plants, leading to substantial reductions in yield and declines in quality. It is prevalent in tea plantations globally. Given the considerable genetic diversity of pathogen populations across various tea-growing regions, understanding the population structure and pathogenic variation of dominant pathogens is essential for the development of sustainable ecological and economic management strategies. In this study, seven isolates of Pseudopestalotiopsis camelliae-sinensis, one of Pestalotiopsis camelliae, and one of Neopestalotiopsis sp. were identified from diseased leaves of Camellia sinensis 'Fudingdabai' in Shaanxi, China. Strain '10' demonstrated the highest pathogenicity and was identified as the primary pathogen responsible for gray blight. By assessing lesion area, leaf architecture, and biochemical constituents, the resistance levels of 20 tea cultivars were classified as highly resistant (one), resistant (four), intermediate resistant (eight), susceptible (five), and highly susceptible (two). Dynamic enzyme activity assays demonstrated a positive correlation between disease resistance in tea cultivars and the activities of peroxidase and phenylalanine ammonia-lyase, establishing a resistance hierarchy as follows: 'Longjingchangye'>'Zhongcha 108'>'Longjing 43'. Notably, cultivars exhibiting resistance showed significantly stabilized superoxide dismutase activity in comparison with susceptible genotypes. Cytological analyses of tea gray blight disease infection in highly resistant ('Longjingchangye'), highly susceptible ('Longjing 43'), and intermediate resistant ('Zhongcha 108') cultivars revealed a significantly reduced presence of appressoria and infection pegs in resistant genotypes relative to the susceptible cultivar. These findings provide a scientific foundation for the breeding of disease-resistant tea varieties and contribute to the understanding of plant-fungal pathogen interaction mechanisms.