Phenological Responses of Rice (Oryza sativa) to Heat Stress and their Regulation by Plant Growth Regulators
R. Manisha *
Department of Agricultural Meteorology, College of Agriculture, KAU, Thrissur, Kerala, India.
B. Ajithkumar
Department of Agricultural Meteorology, College of Agriculture, KAU, Thrissur, Kerala, India.
Arjun Vysakh
Department of Agricultural Meteorology, College of Agriculture, KAU, Thrissur, Kerala, India.
M. S. Parvathi
Department of Plant Physiology, College of Agriculture, KAU, Thrissur, Kerala, India.
A. Latha
Department of Agronomy, College of Agriculture, KAU, Thrissur, Kerala, India.
P. Lincy Davis
Department of Agricultural Meteorology, College of Agriculture, KAU, Thrissur, Kerala, India.
Devanshi Maharana
Department of Agricultural Meteorology, College of Agriculture, KAU, Thrissur, Kerala, India.
K. R. Riya
Department of Agricultural Meteorology, College of Agriculture, KAU, Thrissur, Kerala, India.
Chandana B. Jyothi
Department of Agricultural Meteorology, College of Agriculture, KAU, Thrissur, Kerala, India.
*Author to whom correspondence should be addressed.
Abstract
Rising temperatures threaten rice productivity, particularly when heat stress coincides with sensitive developmental stages. This study evaluated stage-specific phenological, physiological, and yield responses of rice (Oryza sativa L.) cv. Jyothi and examined the mitigating effects of foliar plant growth regulators. A factorial completely randomised design was conducted during the 2025 kharif season using eight temperature-exposure regimes under polyhouse and ambient conditions and four foliar treatments: no spray, water spray, salicylic acid (400 ppm), and brassinosteroid (5 ppm). Heat stress was imposed across the active tillering, heading, and milking stages. Elevated temperature delayed phenological progression and, under severe reproductive-stage stress, prevented flowering, grain filling, and yield formation in several treatment regimes. Heat stress also reduced chlorophyll content and membrane stability index, whereas plant growth regulator treatments improved these physiological traits relative to untreated or water-sprayed plants. Brassinosteroid treatment generally produced the highest chlorophyll content, membrane stability, and yield-related performance, followed by salicylic acid. Yield components, including tiller and panicle number, filled grains, and grain yield, declined under heat stress, with particularly severe effects when reproductive development was exposed to high temperature. The findings indicate that heading is a highly heat-sensitive stage and that foliar brassinosteroid and salicylic acid applications can partially mitigate heat-related physiological and yield impairment in this rice variety under the conditions of the study.
Keywords: High temperature stress, Osmoprotectants, chlorophyll content, membrane stability index, yield.