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.

Drought is considered as one of the main environmental threats for plants that limits the growth and development. In the present study, salicylic acid (SA) was applied to mitigate the drought stress of rubber nursery plants. The study was conducted at Monaragala Sub Station, Rubber Research Institute of Sri Lanka during the dry months from May to September in 2015. The experimental design was Randomized Completed Block Design (RCBD) with five replicates. Treatments were droughtstressed (withholding of water), three concentrations of SA (0.1mM, 0.3mM and 0.5mM) and control(C) kept under regular irrigation. Drought was imposed by withholding water by weekly and lifesaving irrigation was done throughout the nursery period. Measurements were taken on morphological and physiological characters of seedling plants. Plants which were treated with SA as a soil drench at 0.1 mM, 0.3 and 0.5mM concentrations showed significant difference on drought stress plants when compare the stressed plant. Chlorophyll content and stomatal conductance (g s) in seedlings reduced drastically under moisture stressed conditions. Dry matter accumulation also decreased in drought stressed plants as compared to those treated with SA at 0.3 and 0.5mM concentrations. This indicates that the application of SA had a positive effect on stomatal conductance and biomass accumulation under water stressed conditions. In conclusion, the drought-stress decreased the growth of rubber nursery plants to a greater extent and exogenous application of SA at 0.3 mM and 0.5 mM concentrations found to be effective in alleviating drought stress under sub optimal conditions in the Intermediate zone in Sri Lanka.

Session III-Sustainable Agro-forestry Systems 11 ofsoi! diminishes and tea cultivation has caused many environmental problems. Thus, stabilization of a systematic Agro-forestry system in these areas would minimize the environmental problems and would conserve both' Sinharaja' and its peripheral villagers. Further, this kind of stabilization process should go parallel with the prevalent lifestyles and culture of the villagers. Additionally, that process should provide villagers with economical advantages. Moreover, plantation of crop verities in the tea lands should be encouraged as well as animal husbandry, apiculture and plantation of medicinal plant etc. Yet, the contribution and the sponsorship of the government and non-government organizations, plan and policy making ofscientists and the active participation of the peripheral villagers are essential to bring these activities into success.

Rubber industry plays a major role in the economy of Sri Lanka. Two types of commercial ethephon mixtures i.e. water-based and oil-based are presently marketed in Sri Lanka to use as yield stimulant of rubber. Though the yield performance of these mixtures had been studied, no proper investigation has been made on effectiveness of these two types of commercial ethephon mixtures on factors affecting latex regeneration and flow of Hevea brasiliensis. Mature rubber plantation with RRIC 121 genotype tapped on first virgin panel (BO-I) with S/2 d4 (half spiral once in four days) system was selected for the study. Yield related factors and latex physiological parameters of rubber trees stimulated with two types of commercial ethephon mixtures were determined on each tapping day during June -August, 2018. Daily latex volume per tree, daily dry rubber yield per tree (g/t/t), latex thiol content, latex polyphenol content and plugging index showed a similar pattern of variation between the rubber trees stimulated with water-based and oil-based ethephon over the experimental period and the variations were not statistically significant. Oil-based ethephon stimulated rubber trees had a significantly higher latex dry rubber content (43.80±0.37, 42.69±0.47, 42.13±0.50%) than water-based ethephon stimulated trees (40.63±0.36, 39.39±0.42, 39.59±0.36%) over the three consecutive stimulation cycles. Inorganic phosphorus content in latex was found to be 21-23% higher in trees applied with water-based stimulant than oil-based stimulant over the period studied. Oil-based stimulation showed 7-11% increase in latex flow duration than water-based stimulation. Though some physiological parameters of latex have been improved in trees with application of oil-based ethephon, yielding capacity for a particular period was statistically comparable in trees applied with water-based and oil-based ethephon.

Ethephon is an essential agrochemical in low intensity harvesting of rubber (Hevea brasiliensis). Currently the total requirement for rubber industry is being imported in ready-mixed form adding a considerable cost to the plantations. Therefore, a new ethephon formulation was developed locally and the present study aimed to assess its effectiveness under Sri Lankan condition. The newly developed ethephon formulation was tested against a commercially available formulation with a small-scale field trial. No significant variation was observed in sucrose availability in laticifers with the new ethephon formulation. Significantly higher thiol and lower inorganic phosphorous contents of latex in trees may ensure long-term sustainability of the new ethephon formulation as a yield stimulant in rubber. Average dry rubber content of latex and latex volume obtained from a tree was comparable with both formulations. Accordingly, dry rubber yield resulted from trees applied with new ethephon formulation was comparable with the existing formulation and average values were 83.22 g and 86.67 g, respectively for new and existing formulations.