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.

Harvesting latex from rubber trees at different times in the early hours of the day or so-called night tapping has led to more time to extract latex from trees and saves time for the tapper to engage in other farm activities during the daytime in non-traditional areas in Sri Lanka. A night tapping trial was conducted during the 2017-2018 period for one year in Moneragala District (IL1c) to investigate whether night tapping is advantageous for farmers to obtain higher latex yields from their fields. In this study, two smallholder rubber fields were selected in Moneragala District, and trees were tapped at S/2 d2 tapping system without rain guards. For each starting time, 10 trees were allocated for the collection of latex in each treatment, and treatments were set up at five different time intervals i.e., 1.30, 2.30, 3.30, 4.30, and 5.00 for field 1 and from 1.00 am to 5.00 am hourly intervals for field 2. Tapping time at 5.00 am was considered as the control treatment for both fields as the normal tapping time in Moneragala. A forehead-mounted torch was used by each tapper to illuminate the tapping cut. Results revealed that there was a variation in latex yield tapped from 1.00 am to 5.00 am in both fields. The present trial indicated that the latex yields are given at different tapping times before 4.30 am comparatively low in pre-dawn tapping.

Drought and high temperature are the major impediments limiting growth of Hevea. We studied the efficacy of foliar applied Moringa (Moringa oleifera) leaf extract (MLE) as a biostimulant on the response of Hevea to sub-optimal climatic conditions. Rubber plants of clone RRISL 203 cultivated in the Intermediate Zone (IZ) and Dry Zone (DZ) were spray treated with water (mock treatment), MLE at 5, 10 and 15% concentrations for IZ and 3 and 5% for DZ. Physiological parameters viz. net photosynthesis (Pr), chlorophyll content (Cc), stomatal conductance (gs) and leaf water potential (Ψ) were recorded after three months from the commencement of treatments whilst girth measurements were recorded at three and twelve months after treatments in the IZ. Total phenolic content (TPC) and antioxidant activities, employing FRAP (ferric reducing assay power) and ABTS (2,2'-azino-bis-3ethylbenzothiazoline-6-sulphonic acid) techniques, were estimated after three months from first spraying in the DZ. Significantly higher Pr, Cc and gs values were recorded from plants treated with MLE at all three concentrations as compared to control. Significantly higher TPC values (17.17 and 15.90 mg of gallic acid equivalent/ g of leaf sample), and FRAP values (14.79 and 14.70 mg of trolox equivalent/g of leaf sample) and ABTS values (70.26 and 59.43 mg of TE/g of leaf sample) were recorded in plants treated with MLE at both concentrations (3 and 5%) as compared to control (12.50 mg of GAE/g of leaf sample, 10.68 mg of TE/g of leaf sample and 49.96 mg of TE/g of leaf sample), respectively. A significantly higher girth (11.5 cm) was recorded in plants treated with MLE at 5% as compared to control (9.66 cm) after 12 months of treatments. Improved growth and physio-chemical attributes of rubber plants could be attributed to the beneficial effect of MLE as a biostimulant and therefore, exogenous application of MLE could effectively be utilized as an environmental friendly and inexpensive strategy for growth improvement in Hevea under sub-optimal climatic conditions.

The Intermediate and Dry Zones of Sri Lanka have been targeted in expanding the rubber plantations with a view to expand the extent under planting to achieve national targets in natural rubber production. However, climatic conditions of these regions are suboptimal for growing of rubber. The mid-year dry period in these areas extends from June to September and as a result, plants experience a severe water stress especially in nursery and immature period. Therefore, this study was carried out in the Kilinochchi District, which belongs to the Agro-ecological Zone, DL3 in order to assess the performance of micro-irrigation techniques for immature or young rubber plants. Two micro-irrigation systems; viz. drip and spray jet were tested under three soil moisture depletion levels; 30, 50 and 70% of available soil moisture. Results showed that the growth of immature young rubber plants were highly responsive to moisture depletion levels and micro-irrigated systems. It was found that both drip and spray jet irrigation systems performed well in supplying water at 30% depletion level when compared to the depletion levels of 50 and 70%. Water stress is created by 70% depletion level with decreased chlorophyll content, stomata closure and increase in leaf temperature. Adequate irrigation at 30% depletion level in both systems resulted significant increment of chlorophyll content (p< 0.05). There was significant increment in chlorophyll content in plants which were irrigated with spray jet system when compared to drip system. Plants which were irrigated at 30% depletion level regulated higher stomatal conductance even under higher temperatures during mid-day period.