Physiological and Biochemical Basis of Thermotolerance in Selectively Fertilized Coconut Hybrids

The aim of the study was to physiologically and biochemically assess selectively fertilized coconut hybrids for their tolerance to high-temperature stress. Conducted using a two-factorial Completely Randomized Design, the research took place at the Department of Plant Physiology, College of Agriculture, Vellayani, Trivandrum, between October 28, 2023, and December 28, 2023. Methodology involved cultivating six-month-old selectively fertilized hybrid seedlings of three coconut varieties, Kerasree, Keraganga, and Kerasankara, in a polyhouse with a pre-set temperature of 40±1°C for two months. Various physiological and biochemical parameters, including Relative Water Content, Chlorophyll Stability Index, Epicuticular Wax Content, Lipid Peroxidation Level, and antioxidant enzyme activity, were measured to assess stress tolerance. Results showed that for the physiological parameters RWC and CSI, selectively fertilized hybrids varied significantly under high temperatures from their corresponding non-fertilized hybrids, with average mean values of 88.53% and 83.27%, respectively. High-temperature-induced solute leakage was lowest in Kerasankara selectively fertilized hybrids with a mean value of 3.58±0.63, and wax deposition values were on par for selectively fertilized and non-fertilized hybrids. MDA accumulation due to lipid peroxidation was significantly lowest in selectively fertilized hybrids with a mean value of 2.47µg g-1. Antioxidant enzymatic activity in selectively fertilized hybrids was remarkably higher, with significant percent increases of 97.1% for Peroxidase and 96.1% for SOD in the Keraganga selectively fertilized genotype. The study concluded that coconut hybrid accessions developed through pollen selection demonstrated significant superiority over regular hybrids in terms of physiological and biochemical stress tolerance indices. Thus, pollen selection followed by selective fertilization is a reliable, cost-effective, and time-saving approach for breeding stress-tolerant crops, including perennials.