The purpose of this study was to determine the impact of low light stress on the morphological parameters and yield of long duration rice genotypes. The experiment was carried out in the field of National Rice Research Institute, and the field layout was done as per the split plot design, with the light in the main plot and the varieties in the sub-plot. During Kharif 2019, the experiment was carried out at plot-4, V-block under the Department of Crop Physiology and Biochemistry at the National Rice Research Institute (NRRI), Cuttack. The experiment was carried out with three different light intensities, namely 100% light as treatment-I (Control), 75% light as treatment-II, and 50% light as treatment-III. Eleven long duration rice varieties were chosen based on yield to investigate the effect of low light on their morphology and yield. It was observed that at 50% flowering stage in 75% and 50% light intensities, plant height and leaf area increases but tiller number, panicle number and yield reduces. At 50% light intensity, yield reduction was significantly greater than 75% light intensity. Among the varieties Nasati Sali, Nalini Sali and Swarnaprabha was recorded highest grain yield in 100% (5.10 t ha^-1), 75% (4.27 t ha^-1) and 50% light intensity (3.05 t ha^-1) respectively.

Light has a significant role in growth and development of plants because of its crucial role in photosynthesis and photo morphogenesis. If the amount of light intensity reaches the plants is reduced than the optimum level then it creates low light stress for plants and this problem is identified in the eastern and north-eastern region of India which is the major rice belt in our country. Therefore the present experiment was conducted during Kharif 2019 at plot no-4, Block-V of Department of Crop Physiology and Biochemistry, NRRI, Cuttack to study the Low light effect on the biochemical changes and grain yield of long duration rice cultivars. In the present research, 9 long duration rice varieties along with 2 check varieties were exposed to 75% light and 50% light condition in comparison to control (100% light) to know the leaf chlorophyll behaviour and yield during kharif (July‒November, 2019). Plants were grown in field condition with shade installation done 15days after transplanting to impose low light stress in plants. Among the varieties, Swarnaprabha was found with the highest total chlorophyll content in 100% L (2.311 mg g^-1 fresh weight), 75% L (2.705 mg g^-1 fresh weight) and 50% L (3.684 mg g^-1 fresh weight) at 50% flowering stage. Similarly, Swarnaprabha was recorded with the highest chlorophyll at 7 days after 50% flowering. In both the cases, low light induced more chlorophyll in plants than normal light. Among the antioxidant enzymes, Peroxidase and Catalase exhibited an increased activity under low light stress, whereas Superoxide dismutase (SOD) exhibited decreased activity in low light stress. Besides, higher yield was recorded in normal light condition than 75% light and 50% light condition. Among the varieties Nasati Sali leads with higher yield in 100% (5.10 t ha^-1) and 75% (4.27 t ha^-1) light condition. On the other hand Swarnaprabha (3.05 t ha^-1) having highest yield at 50% light intensity.