Screening of Coconut (Cocos nucifera) For Drought Tolerance

Abstract

Drought causes a substantial reduction in the national yield of coconut and also loss of coconut palms in severe droughts, thus resulting in serious economic consequences in the coconut industry of Sri Lanka. Therefore, it is of prime importance to identify some putative drought tolerant genotypes for planting in drought prone areas. As the long generation and maturation periods of coconut restrict the selection of genotypes based on yield, a knowledge on the physiological responses to water deficit conditions plays an important role in developing a rapid selection criterion. Therefore, the objective of this research was to identify drought tolerant genotypes by using the effects of drought on gas exchange parameters of selected coconut genotypes. Four genotypes were selected. The accession Clovis (CL) is believed to be tolerant to drought while the rest (Dwarf Green [DGJ, Dwarf Brown [DB] and Cameron Red Dwarf [CRD]) are considered to be sensitive. All palms were about 15 years of age and managed according to the recommended practices, in adjacent plots at the Poththukulama Research Station, Pallama in ILi Agro-Ecological Region (Aquic Quartzipsamments, uncoated sandy, non-calcareous soil). Eight adjacent palms from each of four genotypes were selected from experimental plots arranged in Completely Randomized Design. Palms were monitored throughout the 80-day natural drought experienced in early 2005. Stomatal conductance (gj, rate of photosynthesis (A), and rate of transpiration (E), were measured during the drought period along with the corresponding soil moisture contents. The reduction in gs in response to drought occurred in all four genotypes. CL and DB appeared more drought tolerant by maintaining higher A even under lower gs during drought. Moreover, CL and DB recovered quickly after subsequent rains. CRD showed highest rale of reduction of gs (63%) with the inception of drought indicating its greater sensitivity to water deficit conditions. The susceptibility index (SI) calculated using gs, E and A/E also showed that CRD was the most sensitive genotype to drought while CL being the most tolerant out of four genotypes. Although DB and DG appeared sensitive to drought in terms of SI, DB showed a degree of tolerance, quick recovery, and higher rates of A and thus showed a greater potential for higher productivity which was important in a commercial cultivation. These four genotypes can be ranked in order of drought tolerance as