Physiochemical traits as potential indicators for determining drought tolerance during active tillering stage in rice (Oryza sativa L.)

It is well known that water scarcity limits crop production and further expansion of agriculture. In order to combat the adverse effect, plants have developed various morphological, physiological, and biochemical responses. Several studies were carried out separately, but there have been limited reports which explored on the combined effects of stress factors. Therefore, the present study was attempted to relate physiochemical traits under water deficit condition and explore the possibility of utilizing it for further crop improvement in rice. Five commercial rice varieties, namely MR-37, MR-84, MR-219, MR-220 and MR-232, were grown in randomized block design replicated thrice. At active tillering stage (i.e. 45 days after sowing), drought was induced by withholding water for a period of 7-10 days. Drought symptom was noticed by wilting of leaves. At the time of wilting, physiological parameters like relative water content (RWC), total chlorophyll content, chlorophyll stability Index (CSI), proline accumulation and protein content were estimated for both stress induced and control plants. Statistical analyses were performed to determine the effect of drought stress on the rice varieties. Significant differences were noticed for the physicochemical traits studied under drought condition. Mean performance of the genotypes also showed a sharp decline in RWC (%), total chlorophyll content, CSI (%), and protein. Meanwhile, free proline accumulation was found to be more in water deficit condition. Correlation coefficient (r) revealed a significant negative association of RWC (%) with total chlorophyll content, chlorophyll stability index (CSI %), proline and protein with, while total chlorophyll content itself had significant positive relation with CSI (%) under water deficit condition. Correlation coefficient clearly demonstrated that reduction in RWC would affect the osmotic adjustment, cell membrane stability, and photosynthetic machinery in crop plants. Estimates of genotypic variance, board sense heritability, and genetic advance revealed moderate to high estimates for RWC (%), CSI (%), and proline. These high estimates indicated that the rice varieties had inherent potential for drought improvement program. Moreover, the physiochemical parameters involved in the study are fair enough to distinguish between tolerance and susceptible genotypes. Therefore, these parameters could be utilized as key indicators for laboratory screening in determining drought tolerance in rice plants.