International Journal of Environment and Climate Change

Upland rice (broadcast summer rice) is a major component of rice production in Assam, particularly during flood and post-flood periods. The present study evaluated selected upland rice cultivars under normal irrigated and aerobic moisture regimes to identify physiological, biochemical and yield-related responses associated with moisture-stress tolerance. The experiment was conducted during the Rabi season at the Department of Crop Physiology, Assam Agricultural University, Jorhat. Five upland rice genotypes (Banglami, Inglongkiri, Boga ahu, Ronga ahu and Bengungutia ahu), selected after preliminary screening from 169 genotypes, were compared with the national check variety CR Dhan in a fractional randomised block design with three replications. Normal plots were maintained at 17-19% soil moisture, whereas aerobic plots were maintained at 7-8% soil moisture through life-saving irrigation. Aerobic conditions reduced mean flag leaf area by 29.94%, photosynthetic rate by 32.10%, internal CO2 concentration by 15.12%, transpiration rate by 12.73%, total leaf chlorophyll content by 22.95%, nitrate reductase activity by 29.78%, panicle number per hill by 29.56%, grain yield by 20.84% and harvest index by 30.26%. In contrast, mean leaf proline content increased by 43.98% under aerobic conditions. Among the genotypes, Inglongkiri recorded the highest grain yield under aerobic conditions (489.89 g m-2), closely followed by Banglami (488.21 g m-2) and Ronga ahu (468.23 g m-2). These genotypes also maintained relatively favourable physiological and biochemical traits under aerobic conditions. The findings indicate that Inglongkiri, Banglami and Ronga ahu may be more suitable for cultivation under aerobic moisture regimes, whereas Boga ahu and Bengungutia ahu showed relatively greater susceptibility to moisture stress in the present study.