Biochemical changes of four different coconut (Cocos nusifera L.) Forms under moisture stress conditions

Drought causes a substantial reduction in national yield of coconut and also a loss of coconut palms in severe droughts thus resulting in serious economic consequences to the coconut industry in Sri Lanka. Therefore, it is of prime importance to identify some putative drought tolerant forms to use in drought-prone areas. As the long generation and maturation periods of coconut restrict the selection of coconut forms based on yield, the knowledge on physiological and biochemical responses to water deficit conditions plays an important role in developing a rapid selection criterion. Therefore, the objectives of this research was to quantify the variations in drought tolerance in selected coconut forms, based on their biochemical responses to progressive soil moisture deficits in the field. Four coconut forms (Clovis, Dwarf Green, Dwarf Brown, Cameron Red Dwarf) were selected for the experiment. Palms were subjected to 80-day natural drought experienced in early 2005. Biochemicals namely leaf proline, total soluble sugar and starch contents were studied during the drought period along with the corresponding soil moisture contents at 50 and 100 cm depths. They showed slightly increasing trends with progressive water stress but not significantly different in between four forms. However, duration of natural drought that occurred during the experimental period was shorter than the dry spells which are commonly observed in the area. Therefore, further research under long dry spells is needed to reach a more comprehensive and repeatable results before coming to a final conclusion.