RESPONSE OF RAPID DECLINE AFFECTED COCONUT (COCOS NUCIFERA L.) PALMS TO MICRO-NUTRIENTS AND COMMON SALT

Abstract

Coconut Rapid Decline (CRD) is a serious disorder of coconut palms(Cocos nucifera L.) in Sri Lanka. A substantial loss of crop is well evidentdue to this disorder. This study aims to determine the effect of micronutrientsand common salt on the performance of CRD-affected palms.Fifteen-years-old, mild, moderate and severe CRD-affected palms, inMakandura Research Station (MRS) of Coconut Research Institute wereused for this study. Affected palms were treated with the micro-nutrients(100 ml of 0.35 % CuS04.5H2 0 and 0.72 % ZnS04.7H2 0 solution/palm, rootfeeding at bi-monthly intervals) or common salt (NaCI, 1 kg/palm/year,surface application in the manure circle). Untreated CRD-affected palmswere used as the control. Leaf nutrient levels before, one and two yearsafter treatment application were analyzed. Vegetative, reproductive andphysiological parameters were measured during two years, after treatmentapplication.Pre-treatment analysis of leaves revealed that Nitrogen (N) and Phosphorus(P) contents were within the sufficiency range and Potassium (K) contentwas above the sufficiency range in CRD-affected palms. Magnesium (Mg),Calcium (Ca), Sodium (Na), Copper (Cu) and Zinc (Zn) contents of thosepalms were below the sufficiency range. The macro and micro-nutrientcontents (except Mg) of apparently healthy palms, adjacent to CRD-affectedpalms were within the sufficiency range for coconut. Therefore, it issuggested that the CRD-affected palms suffer from deficiency of Ca, Na, Cuand Zn. There was a significant difference in Iron (Fe) content among threeseverity stages of CRD-affected palms before initial treatment application,Fe concentration increased with increasing severity.Phosphorus and Ca contents significantly increased in micro nutrient andcommon salt treated palms after one year, compared to before treatmentapplication and control. However, there was no significant increase in leafCu, Zn and Na levels, even after two years of the treatment application. Thepercentage of drooping fronds, size of the spadix, number of female flowers,number and size of nuts and circumference of the trunk were not improvedin treated palms one year after treatment. Two years after the treatment, number of total fronds and functional green fronds in the canopy of affectedpalms were increased by common salt application. The stomatal diffusiveresistance of these palms was also reduced after two years showing animprovement in palm water status. The experiment is in progress to.observe the recovery of symptoms.