Characteristics of Leaf Spot Disease Caused by Didymella Species and the Influence of Infection on Tea Quality.

Leaf spots are the most damaging and common foliar diseases of tea and are caused by several species of fungi. During 2018 to 2020, leaf spot diseases showing different symptoms (large and small spots) were observed in commercial tea plantations in Guizhou and Sichuan provinces of China. The pathogen causing the two different sized leaf spots was identified as the same species (Didymella segeticola) based on morphological characteristics, pathogenicity, and multilocus phylogenetic analysis using the combined ITS, TUB, LSU, and RPB2 gene regions. Microbial diversity analysis of lesion tissues from small spots on naturally infected tea leaves further confirmed Didymella to be present as the main pathogen. Results of sensory evaluation and quality-related metabolite analysis of tea shoots infected with the small leaf spot symptom indicated that D. segeticola negatively affected the quality and flavor of tea by changing the composition and content of caffeine, catechins, and amino acids. In addition, the significantly reduced amino acid derivatives in tea are confirmed to be positively associated with the enhanced bitter taste. The results improve our understanding of the pathogenicity of Didymella species and the influence of Didymella on the host plant, Camellia sinensis.

A New Colletotrichum Species Associated with Brown Blight Disease on Camellia sinensis.

Brown blight, as the most damaging and common foliar disease of the tea plant (Camellia sinensis) in China, has been recently reported to be caused by different species of the genus Colletotrichum. During the years 2016 to 2017, tea plants in commercial tea cultivation areas of Chongqing City that reported significant incidences of brown blight disease were investigated and then analyzed using both morphological characteristics and multilocus phylogenetic analysis. The results showed that at least five species of Colletotrichum were identified, including four well-known species (Colletotrichum gloeosporioides, C. camelliae, C. fioriniae, and C. karstii) and one novel species (C. chongqingense), indicating that there is remarkable species diversity in Colletotrichum spp. present as pathogens. Results of pathogenicity analyses confirmed that C. chongqingense was the causal agent of brown blight and different isolates differed in virulence. C. chongqingense, as a novel pathogen, has never been reported as being associated with brown blight disease in tea plants or anthracnose in other host plants anywhere in the world. Knowledge of the Colletotrichum populations will facilitate further studies addressing the relationships between Colletotrichum spp. and their host plant Camellia sinensis.

Metabolomics Analysis Reveals the Effect of Two Alpine Foliar Diseases on the Non-Volatile and Volatile Metabolites of Tea.

Blister blight and small leaf spots are important alpine diseases that mainly attack tender tea leaves, affecting tea quality. However, there is limited information on the effect of these diseases on tea's non-volatile and volatile metabolites. Metabolomic analysis based on UHPLC-Q-TOF/MS, HPLC and GC/MS was used to reveal the characteristic chemical profiles of tea leaves infected with blister blight (BB) and small leaf spots (SS). Flavonoids and monolignols were non-volatile metabolites that were enriched and significantly changed. Six main monolignols involved in phenylpropanoid biosynthesis were significantly induced in infected tea leaves. The accumulation of catechins, (-)-epigallocatechin gallate, (-)-epicatechin gallate, caffeine, amino acids and theanine were significantly decreased in both diseased tea leaves, while soluble sugar, (-)-epigallocatechin and phenol-ammonia were obviously increased. Among them, the amounts of sweet and umami-related soluble sugar, sucrose, amino acids and theanine were much higher in BB, while bitter and astringent taste-related catechins and derivatives were much higher in SS. Volatiles analysis showed that volatiles content in SS and BB was significantly decreased, and styrene was significantly induced in blister blight-infected tea leaves. The results indicate that the type and amount of volatiles were highly and differentially influenced by infection with the two alpine diseases.