Exogenous Application o f Salicylic Acid with Irrigation to Alleviate Drought Stress of Rubber Nursery Plants in the Intermediate Zone o f Sri Lanka

Abstract

With the increasing demand for natural rubber, the Government of Sri Lanka (GOSL) explores the possibilities of expanding rubber cultivation in to non traditional areas of the country. Drought is considered as one of the main environmental threats in those areas that limits the growth and development of young rubber plants. The present study was conducted to mitigate the drought stress of rubber nursery plants by applying Salicylic Acid (SA) as stress tolerance mediator with irrigation. The study was conducted at Monaragala sub-station, Rubber Research Institute of Sri Lanka under protected conditions during the dry months from February to July in 2013. The experimental design was Complete Randomized Design (CRD) with six replicates. Each replicate was arranged with ten nursery plants. There were five different methods of SA applications as SA (0.5 mM) application at 50% depletion as soil drench, at 50% depletion as foliar applications, irrigated at 50% depletion without SA application (HF), regular irrigating at 10% depletion (RG) and drought stressed at 90% depletion (DR). Measurements were recorded on plant growth, physiological and water relations parameters. Plants which were regular irrigated (RG) and plants which were treated with Salicylic Acid as soil drench (50% + SAS) showed a significantly (p<0.05) higher diameter than the other treatments and it has shown that the application of SA as soil drench with irrigation at 50% depletion alleviates the negative effects and enhances the plant growth under severe drought stress. Stomatal conductance (gs) was reduced strongly under severe drought condition at 90% depletion with compared to other treatments. This indicated that application of SA had positive effects on stomatal conductance and relative water content. In conclusion, the drought stress decreased the plant growth severely and application of 0.5 mM concentration of SA is found to be a promising and feasible option in irrigation scheduling, alleviating drought stress of rubber nursery plants in the Intermediate Zone of Sri Lanka.