Abstract:
The effect of moisture stress on leaf water potential [IP], relative water content [RWC\,
stomatal conductance [gj, transpiration [£"], rate of net photosynthesis [A], leaf temperature
[Tieaj{ and ratio of intercellular and atmospheric CO2 concentration [C/Ca] of
four coconut genotypes (Clovis [CL], Dwarf Green [DG], Dwarf Brown [DB] and Cameron
Red Dwarf [0?D]) were studied, to identify factors that contribute to drought
tolerance of some coconut genotypes and to develop an index for screening drought
tolerant genotypes. All palms were about 15 years of age, grown in ILi Agro-Ecological
Region and were exposed to 80-day natural drought. RWC of leaves showed that the
three dwarf genotypes dehydrated faster than CL. The reduction in gs in response to
moisture stress was observed in all genotypes, even though the IP was not significantly
reduced. This suggests that there is a signal from roots that induces a reduction in gs.
CL and DB appeared more drought tolerant by maintaining high A even under low soil
moisture conditions and by having low gs, while, DB responded quickly to subsequent
rains by regaining its initial rates of photosynthesis and gs. Moreover, CL maintained
lowest Tieaf and highest C/Ca ratio during dry weather. CRD showed highest rate of
reduction of gs with the inception of dry spell, indicating its highest sensitivity to moisture
stress conditions. Based on the index of stomatal performance, calculated by using
gs and IP CRD was selected as the most drought sensitive genotype, and DB as the most
drought tolerant genotype.
