ABSTRACT. The response of some selected physiological and biochemical parameters of tea (Camellia sinensis L.)

No abstract

Weligama coconut leaf wilt disease (WCLWD) causes heavy losses in the coconut cultivations of southern Sri Lanka. The in-house developed and validated indirect ELISA was based on specific polyclonal antibodies raised in female New Zealand White rabbits, against partially purified WCLWD associated phytoplasma. This ELISA has the potential to distinguish secA PCR confirmed, WCLWD associated phytoplasma positive palms from phytoplasma free palms at high accuracy (93%) and sensitivity (92.7%), but with marginal specificity (79%). The calculated ELISA cross reactivity index (CRI) values were low for sugarcane white leaf (7%) and sugarcane grassy shoot (8%) infected leaves, but with marked highCRIfor both Bermuda grass white leaf (69%) and areca nut yellow leaf (70%) infected leaves. SecA gene based phylogenetic relationships of the WCLWD associated phytoplasma with these other locally prevalent phytoplasma strains elucidated this immunological cross reactivity, which was further reiterated by virtual restriction fragment length polymorphism analysis. Based on scanning electron microscopy, this study provides additional visual evidence, for the presence of phytoplasmas in WCLWD infected tissues.

Salicylic acid (SA) has been known to induce drought tolerance in many plant species. In this study, we investigated the potential of exogenous application of SA to enhance drought tolerance in immature tea plants under glasshouse conditions at the Tea Research Institute in Talawakelle, Sri Lanka. One-year-old potted tea cultivars known for drought tolerance were used in the study. The plants were subjected to a drying cycle while being foliar sprayed with different concentrations of SA along with well-watered (WW), water-spray (WS) and no-spray (NS) treatments. Data were collected at 18 hours, 14 days after spraying (DAS), 21 DAS, and during the recovery after re-watering at 21 DAS. Based on the results obtained from the glasshouse study, the effective concentration of 150 mg L-1 SA was selected for further testing under field conditions in Talawakelle using three-year-old tea plants. The field experiment followed a randomized complete block design (RCBD) with three blocks. When the plants reached a moderate moisture stress level, they were foliar-sprayed with 150 mg L-1 SA, WS and NS treatments were included as controls. Data were collected at 7 DAS, 14 DAS, 21 DAS, and during the recovery phase after rain. The results showed that drought stress led to a decline in gas exchange parameters, relative water content, and an increase in the accumulation of osmolytes. However, the exogenous application of 150 mg L-1 SA significantly improved physiological processes such as gas exchange, osmolyte accumulation, and antioxidant activity, thus effectively enhancing drought tolerance in immature tea plants.