Enhancement of growth and seed yield of rice (Oryza sativa L.) through foliar spray of osmoprotectants under high temperature stress

Abstract

An investigation was undertaken during rabi-summer season of 2016-17 in the Department of Seed Science and Technology, OUAT, Bhubaneswar to study the efficiency of some osmoprotectants in mitigating high temperature stress by improving growth, seed yield and quality of rice cv. Naveen. The field experiment was conducted in Split Plot Design, with three replications. The main plot factor was three dates of sowing (D₁ – 30^th November, D₂ – 15^th December and D₃ – 30^th December). The sub-plot factor was foliar spray of chemicals at vegetative and seed filling stages: Control (T₀), 600 ppm Glycine betaine (T₁), 400 ppm Salicylic acid (T₂), 800 ppm Salicylic acid (T₃), 10 ppm Ascorbic acid + 1.3% Citric acid (T₄), 150 ppm α-Tocopherol (T₅), 1.0% Potassium chloride (T₆), 5 ppm Brassinolides (T₇) and 10 ppm Brassinolides (T₈). Observations on various phenological, seed yield and quality parameters were recorded. With advancement in sowing time, there was significant decrease in the chlorophyll content of leaves. The chlorophyll content of leaves after two days of spraying as slightly higher than that prior to spraying in all the treatments. Maximum chlorophyll content was recorded with spray treatment of 800 ppm salicylic acid at both the stages of observation. Significantly higher pollen viability and seed set were recorded with first date of sowing (D₁), compared to second and third dates of sowing (D₂ and D₃, respectively). Among the treatments, pollen viability was highest with 10 ppm brassinolides and 400 ppm salicylic acid. Seed set was highest with 10 ppm brassinolides and 800 ppm salicylic acid. With advancement in sowing time, there was decrease in membrane stability index of leaves. The MSI of leaves after two days of spraying was slightly higher than that prior to spraying in all treatments. Maximum MSI was recorded with spray treatment of 400 ppm salicylic acid (T₂) during vegetative and seed filling stages. The treatments T₂, T₄ and T₈ produced highest increase in MSI compared to that before spraying during both stages. Higher seed yield was obtained from D₁, compared to delayed sowing. Mean seed yield from D₁ was 53.76 q/ha, as against 48.99 q/ha and 44.51 q/ha from D₂ and D₃, respectively. Spraying of 800 ppm salicylic acid and 10 ppm brassinolides gave highest seed yields from each date of sowing. Seed yields from D₃T₀ and D₂T₀ (35.33 q/ha and 39.72 q/ha, respectively) were significantly lower than all treatment combinations, including D₁T₀ (51.83 q/ha). Increase in seed yields due to various treatments as against the control was more pronounced in D₂ and D₃. The first date of sowing (D₁) produced seeds with higher 1000-seed weight (22.62 g), compared to D₂ and D₃ (20.27 g and 19.36 g, respectively). Among the treatments, higher 1000-seed weights were recorded with the treatments T₃ and T₈ (21.51 g and 21.43 g, respectively), while lowest 1000-seed weight (18.76 g) was recorded with the Control. Seeds produced from D₁ recorded higher germination and seed vigour. All the treatments recorded improvement in germination and vigour of seeds with three dates of sowing. Treatments T₃, T₇ and T₈ gave highest improvement in seed germination over control. Under accelerated ageing treatment, T₃ recorded highest germination followed by T₈. Dates of sowing and treatment sprays had no influence on electrical conductivity of seed leachate. Hence, the present study demonstrated that foliar sprays at vegetative and seed filling stages with 800 ppm salicylic acid or 10 ppm ascorbic acid + 1.3% citric acid or 10 ppm brassinolides were quite effective in alleviating adverse effects of high temperature during flowering and seed set, through increased chlorophyll content of leaves, improved membrane stability, higher pollen viability and seed set, thus improving seed yield and quality of rice.