CHANGES IN THE PHYSIOLOGICAL PERFORMANCE OF LEAF SCORCH DECLINE (LSD) AFFECTED COCONUT (COCOS NUCIFERA) PALMS

Abstract

Leaf scorch decline (LSD) is a disorder of coconut (Cocos nucifera) palms in Sri Lanka. The etiology of the disorder is not yet known. This study aimed to compare and quantify physiological and biochemical characters of LSD-affected palms with healthy palms. Thirty-year-old apparently healthy and LSD-affected (mild, moderate and severe) palms (variety typica) were compared at Bandirippuwa Estate, Coconut Research Institute, Sri Lanka. In LSD-affected coconut palms, the functional leaf area of the canopy, rates of photosynthesis and transpiration, leaf water potential, leaf chlorophyll and Zn contents were appreciably reduced with the development of the disorder, whereas stomatal diffusive resistances and abscisic acid concentrations in the xylem sap increased. The volume of inflorescence sap collected from LSD-affected palms was reduced compared to healthy palms, but the composition of the sap remained unaltered. Since altered stomatal behaviour might affect gas exchange and related processes, such as water movement, photosynthesis and the assimilate partitioning pattern, these results support the hypothesis that stomatal closure in LSD-affected palms may influence LSD symptoms. However, more research is needed to come up with conclusive evidence of its cause.