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Abstract
Obstructions to the movement of water, by physical blockages in the vascular system, are a possible cause of the Leaf Scorch Decline (LSD) disorder of coconut palms. This hypothesis was tested by comparing the pattern of water movement in healthy and LSD-affected coconut palms, using Lithium, a non-radioactive tracer, as an indicator. Pattern of water transport in the leaf canopy of healthy and LSD-affected palms was similar but the quantities transported were different. Less water movement in moderate-LSD palms than in healthy and mild-LSD palms suggest the development of obstructions to water movement when the disorder increases in severity. Uptake of water into the root system was not affected by the LSD disorder. However, in moderate-LSD palms more water was retained in the roots than in healthy and mild-LSD palms. This also points to restrictions to water movement in the moderate-LSD palms. The relatively high amounts of Li retained in the roots of healthy and mild-LSD palms need further investigation. Key words: Leaf Scorch Decline, visible symptoms, pattern of water movement, non-radioactive tracer doi: 10.4038/cocos.v18i0.986 COCOS (2007), 18
Highlights
The characteristic visible symptom of the Leaf Scorch Decline (LSD) disorder is leaf scorch that starts from the tips of the leaflets and advances towards the midrib of the frond (Davis, 1962; Ekanayake, 1964, Rajapaksha and Fernando, 1995; Madurapperuma et al, 2004; Ranasinghe, 2005)
This study aims to test the hypothesis, and identify the zones where restrictions occur, using Lithium as a non-radioactive tracer
The high Li concentration in the treated roots of both healthy and LSD palms indicates that the uptake of water is not obstructed when it is supplied directly to the roots
Summary
The characteristic visible symptom of the Leaf Scorch Decline (LSD) disorder is leaf scorch that starts from the tips of the leaflets and advances towards the midrib of the frond (Davis, 1962; Ekanayake, 1964, Rajapaksha and Fernando, 1995; Madurapperuma et al, 2004; Ranasinghe, 2005). Physiological studies with LSD-affected coconut palms have demonstrated a significant reduction in the transpiration rate, photosynthesis and leaf water potential (LWP); and an increase in leaf stomatal resistance and ABA concentration in the xylem sap, in comparison to healthy palms (Jayasekara et al, 1989; Ranasinghe, 2005). This suggests that LSD-affected palms are water stressed. This condition could be attributed to either poor water absorption due to a paucity of live roots in LSD-affected palms (Jayasekara and Premasiri, 1986; Mahindapala and Chandrasena, 1975; Ranasinghe et al, 2002), or physical blockages in the water transport tissues
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