Effect of Early-Season Soil Moisture Stress on Growth and Development of Different Rice Cultivars.

Drought stress in rice affects several crop growth and physiological processes.  However, in order to increase the sustainability of rice production in the US Mid-South, producers are now considering intermittent irrigation, instead of continuous flooding, as a management strategy to increase rainfall capture and reduce water pumping. Moreover, in the Mississippi Delta where permanent flooding is established after V4 growth stage, rice seedlings may be subjected to early-season moisture deficits. A greenhouse experiment was, therefore, conducted to evaluate the performance of 15 commonly grown rice cultivars to early-season soil moisture stress. The rice seedlings were subjected to three different soil moisture regimes – i.e. 100, 66, and 33% field capacity, from 10 to 30 days after sowing (DAS). Morpho-physiological parameters including root traits were measured during the stress period (25 to 30 DAS). Significant moisture stress X cultivar interactions were found for most parameters. A cumulative drought response index (CDRI) was developed by summing the individual response indices of all cultivars. The CDRI values generated varied from 22.87 to 30.72 for the cultivars tested. Rice cultivars, Cocodrie, Lakast, CL152, XL753, CL XL729, CL XL745, and RU1204122 showed low CDRIs, Cheniere, Mermentau, Rex, CL 111, and RU1304154 showed moderately low CDRIs, and CL142AR, CL151, and RU1104122, recently released at CL163, showed high drought tolerance. Significant linear correlation (R² = 0.61) was obtained for root to shoot parameters using regression analysis. The drought tolerance ratings among the rice cultivars will help rice producers select a variety best suited to their rice growing environments.  Additionally, rice breeders may select the drought tolerant varieties identified as parents to develop cultivars adapted to current and future rice growing conditions.