Physiological and biochemical responses of Camellia sinensis to stress associated with Empoasca vitis feeding

The tea green leafhopper, Empoasca vitis, is the most serious pest in plantations of tea, Camellia sinensis. Beyond physical damage to the leaves, tea yields may be affected if feeding stress causes physiological and biochemical changes in the tea plant, which affected the quality and flavor of the tea. Yet the effect of feeding stress, induced by E. vitis, is largely unknown. We measured the injury index and the physiological and biochemical responses of C. sinensis to stress by E. vitis feeding in a series of laboratory trials. Using 2-year-old C. sinensis plants, we tested the effects of leafhopper feeding at different densities—0, 5, 10, and 20 leafhoppers—and different durations of exposure—1, 4, 7, and 10 days—on potential changes in chlorophyll, tea polyphenols, nutrient content, activities of protective enzymes (peroxidase, POD; superoxide dismutase, SOD; and catalase, CAT), and the lipid peroxidation (MDA). We found that the injury indices for tea leaves increased continuously as the density of E. vitis increased in the same day, and simultaneously, as the time of leafhoppers damage increased, the injury indices for tea leaves also increased. Our results also indicated that feeding by E. vitis caused a considerable decline in chlorophyll a, chlorophyll b, total chlorophyll in tea leaves and soluble carbohydrate content, and an increase in tea polyphenols. Soluble protein content showed a direct increasing relationship with the increasing leafhopper density and the duration of exposure. Throughout the period of E. vitis exposure, there was highly significant difference in the activities of protective enzymes and MDA content. Additionally, POD, SOD, and CAT activities in tea leaves were elevated significantly with the increase of leafhopper density. Lipid peroxidation (MDA) content also increased after the exposure to leafhopper feeding. Overall, our results indicate that although C. sinensis displays a certain level of tolerance to E. vitis feeding stress, higher density of leafhoppers, and longer exposure duration, can cause severe damage to tea leaves and also a decline in plant defense of tea, so as to affect the tea quality.