Rice (Oryza sativa L.) stands as one of the most critical staple crops globally, with its yield and water use efficiency (WUE) being pivotal for food security. This study aimed to evaluate the agronomic and physiological traits and WUE of six rice varieties under two irrigation regimes: alternate wetting and drying (AWD) and conventional irrigation (CI). The results showed the significant improvements in grain yield and WUE with variety improvement under both irrigation treatments. Under AWD, high water use efficiency varieties (HWVs) demonstrated pronounced enhancements, including tillers and spikelet production, filled grain rate, 1000-grain weight, harvest index, leaf area index, non-structural carbohydrate remobilization, photosynthesis and catalase and peroxidase activities of leaf, root and shoot biomass, and root activity. AWD was observed to synchronize and amplify grain yield (2–14%) and WUE, including both leaf-level (13.94–20.72%) and yield-level (23.20–30.87%) water use efficiencies (WUE_L and WUE_Y). The water use potential for HWVs was substantially enhanced under AWD. The integration of variety improvement with AWD irrigation strategies effectively achieves the dual objectives of high yield and WUE, offering a promising approach for sustainable rice production.

The way in which alternate wetting and drying irrigation (AWD), as a water-saving practice promoted in rice (Oryza sativa L.) production systems, could enhance the productivity and water use efficiency (WUE) attracts broad attention. This study selected six mid-season indica rice varieties to investigate the impacts of AWD and conventional irrigation (CI) on grain yield, WUE, grain filling, and root traits. A two-year field experiment demonstrated that grain yields and WUE were significantly increased with varietal improvements. With the improvement of varieties, the maximum grain filling rate and mean grain filling rate for both apical superior and basal inferior spikelets were progressively enhanced during the grain filling stage. Compared to CI, AWD significantly enhanced grain yield and WUE. Flag leaf photosynthetic rate and root characteristics, including root weight, root length, root absorbing surface area, root oxidation activity, and zeatin (Z) + zeatin riboside (ZR) contents in panicles, roots, and root bleeding, were superior under AWD across early, mid, and late grain filling stages. Correlation and path analysis showed that improved grain filling in basal inferior spikelets was attributed to delayed root senescence during the grain filling stage under AWD. These results indicated that AWD would be a better irrigation regime to improve yield and WUE by optimizing grain filling and root growth for modern varieties.

Enhancing rice (Oryza sativa L.) productivity and optimizing water use efficiency (WUE) are critical for advancing sustainable agricultural practices. This study selected six mid-season indica rice varieties to investigate the impacts of alternate wetting and drying irrigation (AWD) and conventional irrigation (CI) on grain yield, WUE, grain filling, and root traits. A two-year field experiment demonstrated that AWD significantly enhanced grain yield and WUE. Flag leaf photosynthetic rate and root characteristics, including root weight, root length, root absorbing surface area, root oxidation activity, and zeatin (Z) + zeatin riboside (ZR) contents in panicles, roots, and root bleeding, were superior under AWD across early, mid, and late grain filling stages. The flag leaf photosynthetic rate and root traits, such as root weight, root length, root absorbing surface area, root oxidation activity, and zeatin (Z) + zeatin riboside (ZR) contents in panicles, roots, and root exudates, were found to be superior under AWD during the early, mid, and late grain filling stages. Notably, AWD delayed root senescence during the grain filling stage, which sustained root activity and promoted grain filling, particularly in inferior spikelets. These results indicate that AWD is a promising irrigation regime to improve rice yield and WUE by optimizing grain filling and root traits.