Physiological and Agronomic Insights Into Water Use Efficiency Differences Among Mid-Season Indica Rice Varieties

A major challenge in rice (Oryza sativa L.) production is addressing freshwater scarcity without compromising grain yield. Identifying rice varieties with high yield and water use efficiency (WUE) is critical for sustainable agriculture. However, limited information exists regarding the agronomic and physiological traits associated with varying WUE. In this 2-year field study, six mid-season indica rice varieties with different WUE levels were categorized as low (LWVs), medium (MWVs), and high WUE varieties (HWVs). Agronomic and physiological traits were systematically evaluated. The HWVs exhibited significantly higher grain yield and WUE, accompanied by a greater productive tiller percentage, harvest index, and leaf area index (LAI) at key stages. These varieties also showed an increased grain-leaf ratio, flag leaf length and width, specific leaf weight and nitrogen content at heading, and an enhanced net photosynthetic rate during panicle initiation, heading, and mid-grain filling. Additionally, HWVs had higher non-structural carbohydrate (NSC) levels in stems and sheaths, elevated antioxidant enzyme activities (catalase, peroxidase, superoxide dismutase), and superior root biomass, root oxidation activity, and zeatin + zeatin riboside (Z + ZR) contents. Principal component analysis revealed that productive tiller percentage, effective LAI, leaf photosynthesis, root dry weight, and Z + ZR levels in leaves were strongly associated with yield and WUE. These results suggest that enhanced shoot and root traits contribute to high WUE and yield performance. This study provides clear guidance and data support for screening rice varieties suitable for water-limited conditions, contributing to sustainable rice production and food security.