Physiological intervention for mitigating temperature stress in rice

Abstract

Rice is an important cereal crop which is most widely consumed as staple food by millions of people. Demand for rice is projected to increase across globe with rapid increase in population. Rice being a tropical crop requires a fairly high temperature for optimum growth and development. However, temperatures above 35 0C cause heat injuries in rice including changes in morphological, physiological and yield characters. Hence, the present study was conducted to identify ameliorative chemicals to mitigate high temperature stress, which is a common occurrence in the third crop season where temperatures can go up to 40 0C in the reproductive stage leading to yield loss. Popular rice varieties, Uma and Manuratna, which are also suitable for the third crop season were chosen for the study. The whole study was divided in to two experiments. The first experiment was carried out in glass house at College of Horticulture, Vellanikkara during January to May, 2019. Ten day old rice seedlings of Uma (V1) and Manuratna (V2) were planted in pots. Treatments included five ameliorative sprays viz. Ascorbic acid (T1), Glutathione (T2), Melatonin (T3), Salicylic acid (T4) and Hoagland solution (T5) along with Water sprayed (T6) and Unsprayed (T7) controls. Ameliorants were sprayed at active tillering stage (S1), booting stage (S2) and both active tillering and booting stages (S3). Physiological responses were studied from this experiment. Pot culture study showed that ameliorants could improve physiological characters of rice under increasing temperature. Hoagland solution spray enhanced photosynthetic rate, stomatal conductance, IAA content and pollen viability in both the varieties. Increased total soluble protein content, chlorophyll a, chlorophyll b and total chlorophyll was noted in plants sprayed with melatonin. Proline accumulation increased in plants sprayed with glutathione while nitrate reductase enzyme activity improved by salicylic acid. Reduced amount of reactive oxygen species as evidenced by histochemical studies was observed in plants sprayed with ameliorants having antioxidant property, like melatonin, glutathione and ascorbic acid. Spraying of ameliorants at both active tillering and booting stages (S3) was the best followed by spraying at booting stage (S2) alone. Second experiment was carried out in Agronomy farm at College of Horticulture, Vellanikkara during February to June, 2020. Twenty day old seedlings of Uma and Manuratna were transplanted to micro plots of 4 m2. Ameliorants were given as foliar spray at booting stage and one plot of each variety was maintained as control for comparison. Biometric observations and yield characters were studied from this trial. Hoagland solution and salicylic acid treatments increased plant height, RGR and CGR in both the varieties. Reduced tiller decline was also observed in Hoagland solution treated plants. Uma showed higher response to ameliorants than Manuratna. Yield parameters were analyzed by comparing response of ameliorants with control. Plants sprayed with Hoagland solution showed better performance with higher grain yield. It was due to increased number of productive tillers, spikelets per panicle, filled grains per panicle and thousand grain weight. Chaff percentage decreased by application of ameliorants and among them Hoagland solution spray gave the best result. Salicylic acid applied plants had higher straw yield compared to other treatments. Yield performance was better in Uma compared to Manuratna.