Assessment of Drought Tolerance Degree (DTD) method as a reliable tool for early-stage screening for drought tolerance in indica rice

Drought stress poses a significant threat to rice production, particularly in indica cultivars that form the staple diet for a large portion of the world's population. Efficient and reliable screening methods are essential to accelerate the development of drought-tolerant rice varieties. The objective of the study was to assess and validate the efficacy of the Drought Tolerance Degree (DTD) method for early-stage drought tolerance screening in a diverse population of 118 doubled haploid (DH) indica rice lines and their parents. Plants were subjected to controlled severe drought stress under pot culture in a net house environment, and drought responses were assessed using DTD method alongside key physiological traits including relative water content (RWC), chlorophyll content index, leaf rolling and drying scores, leaf canopy temperature, leaf area, tiller and leaf numbers, and plant height. The DTD values exhibited strong positive correlations with RWC (r = 0.771) and chlorophyll content (r = 0.526), and strong negative correlations with leaf rolling (r = -0.850), leaf drying scores (r = -0.778), canopy temperature, and tiller number. Principal component and hierarchical clustering analyses further confirmed the association of DTD with drought tolerance-related traits and effectively discriminated tolerant and susceptible genotypes. In comparison with traditional methods, the DTD assay is cost-effective, rapid, and requires minimal technical expertise, making it practical for high-throughput screening in breeding programs. However, its applicability is limited to early growth stages due to the confounding effects of natural leaf senescence at maturity. Overall, this work demonstrates the reliability and efficiency of the DTD method in assessing drought tolerance in indica rice, offering a valuable phenotyping tool to facilitate the selection of drought-resilient cultivars in breeding pipelines.