Characterization of vegetative stage responses in four rice genotypes (Oryza sativa L.) under drought stress: integrating morpho-physiological, biochemical traits and DEG analysis

Drought stress is a significant abiotic stress challenging crop production globally and future food security. The morphological, physiological, and biochemical traits of rice (Oryza sativa L.) are adversely impacted by drought stress, severely affecting its production. In this study, we aim to recognize the best genotypes among four rice genotypes with a combination of adaptive traits under drought stress by investigating the impact of drought stress on morpho-physiological and biochemical traits at the vegetative stage associated with drought tolerance. We conducted a pot experiment during the dry season of 2021 to explore the variations in accumulation and degradation activities of different traits of four rice genotypes at regular stress intervals. Drought stress decreased relative water content by 32.86%, total chlorophyll content by 40.15%, leaf water potential by 2.26-fold, total soluble sugar by 57.47% while increase in canopy temperature by 25.15%, proline accumulation by 65.54%, catalase activity by 65.38% and peroxidase activity by 70.20% were observed at 12 days after stress. Genotypes cultivated under well-watered conditions exhibited no symptoms and had the highest value of all the measured traits except leaf rolling, proline accumulation, canopy temperature, catalase activity, and peroxidase activity. The real-time quantitative reverse transcription PCR (qRT-PCR) was conducted to understand the expression pattern of the genes OsWRKY30, OsAP37, EDT1, ZIP10, and AB15 at the vegetative stage. The expression was detected in four rice genotypes and was found up-regulated by drought stress which are associated with the induction of several drought stress-resistance genes in drought condition. The overexpression of these genes was found in Sahbhagi Dhan and Brahman Nakhi and the expression of these genes were significantly reduced in IR64 and IR20. These findings suggest that the genes might be involved in the drought tolerance mechanism in rice by mediating the transcript levels of some drought stress-resistant genes. The identified tolerant rice genotypes can be employed in breeding projects to increase drought tolerance or water use efficiency in the vegetative stage.