EFFECT OF MELATONIN ON MORPHO-PHYSIOLOGY, GROWTH AND YIELD PERFORMANCE OF BORO RICE UNDER DROUGHT STRESS

Abstract

Drought stress adversely affect plant growth and development. Melatonin (N-acetyl-5- methoxytryptamine) plays an essential role in abiotic stress but its role in alleviating drought stress in rice is not clear. Therefore, the present study investigated the effect of melatonin application on plant growth, physiological responses, and yield performance in rice under drought stress. Oryza sativa L. cv. BRRI dhan29 was the planting material. The experiment was laid out in Randomized Complete Block Design (RCBD). Rice was grown with 0 and 100 µM melatonin alone or in combination with drought. The control plant was watered as per requirement while the others were subjected to drought stress by withholding water. Treatments were applied 15 days after transplanting. The treatments were: Control (C), 100 µM melatonin (M), withholding of water for 10 days (D1), D1+M, withholding of water for 20 days (D2) and D2+M. Drought stress resulted higher proline accumulation in rice plants. This indicates the drought-induced osmotic stress. Relative water content (RWC%) of drought affected rice plants decreased noticeably. Drought caused oxidative stress and disrupts membrane properties which is clear from decreased value of leaf membrane stability index (MSI%). The reduced SPAD value indicates breakdown of chlorophyll pigment or hindering its biosynthesis. Drought decreased the vegetative growth and reproductive development of rice plant. Exposure of rice plants to drought stress decreased plant height, no. of tillers plant , leaf area, dry weights of root, shoot, leaf and total dry matter (TDM) plant , panicle length, no. of spikelet panicle -1 ,

1000 grain weight and finally decreased the grain yield plant -1 . Therefore, drought stress altered the physiological and biochemical processes of rice plants. The visible effect of drought stress was reduction of different growth parameters and alteration of phenological processes. Drought exerted negative effects on the reproductive and yield attributes and finally the yield of rice decreased significantly. Exogenous application of melatonin alleviated the adverse effect of drought stress to some extent, compared to drought affected plants without melatonin. Exogenous melatonin addition improved MSI value under drought stress. Melatonin addition restored the RWC in drought affected rice plants, compared to drought stress alone. Melatonin increased chlorophyll content under drought stress. Melatonin added drought treated rice plants showed improved physiology, growth, reproductive development and the yield. This study suggests that melatonin can be exploited as drought alleviating elicitor.