Impact of Foliar-applied Signal Molecules on Morpho-physiological and Biochemical Responses of Rice (Oryza sativa. L) under Salinity Stress

Background: Plants have developed several adaptive mechanisms to cope with salt stress, including the accumulation of compatible solutes such as proline. Plant Growth Regulators (PGRs) are also critical signaling molecules, helping plants mitigate salt stress through various physiological and developmental changes. Aims: The present study highlights the effect of foliar application of signal molecules on morpho – physiological and biochemical parameters of rice under salinity stress. Methodology: This is a Randomized block design, carried out at Agricultural College Farm, Bapatla, Andhra Pradesh during kharif during 2023-24. The experiment was carried out with two contrast varieties (MCM103- Salt tolerant, as a check; BPT 5204- Salt susceptible) and with eight treatments viz., MCM 103 (Check variety) - T1, 0.25 mM/L of SNP - T2, 0.50 mM/L of SA -T3, 0.50 mM/L of BR -T4, 0.25 mM/L SNP+ 0.50 mM/L SA -T5, 0.25 mM/L SNP+ 0.50 mM/L BR -T6, 0.25 mM/L SNP+ 0.50 mM/L SA+ 0.50 mM/L BR -T7 and No spray control -T8 in three replications. Root samples were meticulously extracted from each treatment plot at three developmental stages: maximum tillering, panicle initiation, and anthesis. Proline was selectively extracted from plant tissues using aqueous sulfosalicylic acid, and its concentration was quantified using the ninhydrin method. Lipid peroxidation was assessed by measuring malondialdehyde (MDA) levels in plant tissues. Results: The present study revealed that the salt-tolerant MCM 103 recorded superior performance over salt salt-sensitive BPT 5204 under salinity stress. The foliar application of signal molecules had positive effects on leaf water potential, chlorophyll stability index, root dry weight and volume, proline, MDA, SOD, Catalase, Na+/K+ ratio. The treatments considerably affected superoxide dismutase (SOD) activity. At maximum tillering, MCM 103 exhibited the highest SOD activity (1.86 U/g FW min⁻¹), with no significant changes observed in BPT 5204. In later stages, all treatments demonstrated elevated SOD activity, with the peak activity noted in plants treated with 0.25 mM/L SNP+ 0.50 mM/L SA+ 0.50 mM/L BR, comparable to MCM 103. Conclusion: Among all the foliar treatments, the foliar application of 0.25 mM/L of Sodium nitroprusside + 0.50 mM/L of Salicylic acid + 0.50 mM/L of Brassinosteroids was found to be the best, significantly improved morpho–physiological and biochemical parameters and was consistent with MCM 103 under salinity stress.