Soil salinity is one of the most challenging environmental factors affecting rice productivity, particularly in regions with high saline soils such as Egypt. The ability of rice to maintain high yield and quality under saline stress is often limited, leading to significant reductions in productivity. With the increasing salinization of agricultural lands, finding effective agronomic practices and treatments to mitigate salt-induced damage in rice crops is critical for ensuring food security. This study investigates the potential of exogenous glycine betaine (GB) and proline (Pro) applications to mitigate the adverse effects of salt stress on rice (cv. Sakha 108) over two consecutive growing seasons (2021-2022). Treatments of 30 mM GB and 30 mM Pro significantly enhanced dry weight (162.2 and 169.7 g in 2021 and 2022, respectively), plant height (88.94 and 99.00 cm), tiller number (10.58 and 10.33), and grain yield (4.22 and 4.30 t/ha) compared to control groups. Combined treatments of 30 mM GB and 30 mM Pro exhibited the greatest improvements across both years, with maximum dry weight (193.44 and 186.56 g), plant height (112.00 and 112.33 cm), tiller number (15.33 and 16.28), spikelet number per meter (264.00 and 264.05), thousand-kernel weight (70.00 and 73.2 g), and grain yield (6.17 and 6.64 t/ha). Additionally, the combined treatments resulted in the highest harvest index (53.22% in 2021 and 48.94% in 2022), amylose content (24.24% and 20.09%), and protein content (12.33% and 12.00%). Correlation analysis highlighted strong positive relationships among traits, such as plant height with grain yield (r = 0.94), biomass yield (r = 0.92), and harvest index (r = 0.90). Path analysis further demonstrated that thousand-kernel weight and biomass yield had the most significant direct effects on grain yield, with values of 0.43 and 0.42, respectively. Heatmap clustering and principal component analysis (PCA) confirmed the synergistic effects of combined GB and Pro treatments, with the 30P_30GB treatment consistently clustering with high-yield traits, enhancing nitrogen use efficiency and stress resilience. In conclusion, the combined application of glycine betaine and proline significantly enhances the agronomic and chemical traits of rice under salt stress. This study demonstrates that these osmoprotectants improve vegetative growth, grain yield, and quality, with synergistic effects observed at optimal concentrations. The findings highlight the potential of glycine betaine and proline as effective tools for improving salt tolerance in rice, offering practical solutions to address challenges in saline-affected agricultural regions.

Salt stress has become a major limiting factor of rice (Oryza sativa L.) yield worldwide. Appropriate nitrogen application contributes to improvement in the salt tolerance of rice. Here, we show that improvement in nitrogen-use efficiency increases salt stress tolerance in rice. Rice varieties with different nitrogen-use efficiencies were subjected to salt stress; they were stimulated with 50, 100, and 150 mmol/L of NaCl solution at the seedling stage and subjected to salinities of 0.2, 0.4%, and 0.6% at the reproductive growth stage. Compared with nitrogen-inefficient rice varieties, the nitrogen-efficient rice varieties showed significant increases in the expression levels of nitrogen-use-efficiency-related genes (TOND1 and OsNPF6.1), nitrogen content (5.1-12.1%), and nitrogen-use enzyme activities (11.7-36.4%) when under salt stress conditions. The nitrogen-efficient rice varieties showed a better adaptation to salt stress, as shown by the decrease in leaf-withering rate (4.7-10.3%), the higher chlorophyll (3.8-9.7%) and water contents (1.1-9.2%), and the better root status (7.3-9.1%) found in the rice seedlings under salt stress conditions. Analysis of physiological indexes revealed that the nitrogen-efficient rice varieties accumulated higher osmotic adjustment substances (9.7-79.9%), lower ROS (23.1-190.8%) and Na+ (15.9-97.5%) contents, higher expression levels of salt stress-related genes in rice seedlings under salt stress conditions. Furthermore, the nitrogen-efficient rice varieties showed higher yield under salt stress, as shown by a lower salt-induced decrease in 1000-grain weight (2.1-6.2%), harvest index (1.4-4.9%), and grain yield (2.8-4.1%) at the reproductive growth stage in salinized soil. Conversely, the nitrogen-efficient rice varieties showed better growth and physiological metabolism statuses under severe salt stress conditions. Our results suggest that nitrogen-efficient rice varieties could improve nitrogen-use and transport efficiency; accordingly, their use can improve the gene expression network, alleviating salt damage and improving grain yield under severe salt stress conditions.

Soil salinization has resulted in a significant decrease in crop yields, particularly affecting the production of crops like rice (Oryza sativa L.). Prohexadione calcium (Pro-Ca) can enhance crop resilience against failure by managing plant height. However, its impact on various tiller positions during the tillering phase of rice under salt stress remains unknown. This study explores the distinct effects of salt stress on the physiological traits of the main stem and different tiller segments of rice plants, along with the role of Pro-Ca in mitigating salt stress. The findings revealed that under salt stress conditions, the number of tillers and leaves on the main stem decreased significantly in rice. Moreover, the levels of malondialdehyde (MDA) and H2O2 in the leaves and stems of each tiller position notably increased. The percentage of tillers experiencing reduction or elevation was higher than that of the main stem compared to the respective control. Application of Pro-Ca through foliar spraying under NaCl stress effectively alleviated the impact of salt stress on the tiller growth of rice during the tillering phase. It also boosted the activities of antioxidant enzymes like superoxide dismutase (SOD) and peroxidase (POD) in the leaves and stems of the tillers. Furthermore, it successfully mitigated the damage inflicted by salt stress on the cell membrane of rice tillers during the tillering phase. The regulatory effect of calcium on cyclic acid was particularly pronounced in alleviating the impact on the tillers under salt stress conditions.

Spikelet degeneration in rice (Oryza sativa L.) is a serious physiological defect, and can be regulated by soil moisture status and phytohormones. This study investigated the possibility that brassinosteroids (BRs) in collaboration with abscisic acid (ABA) are involved in mediating the effect of soil drying during meiosis on spikelet degeneration in rice. Three rice cultivars were field grown and three irrigation regimes including well watered (WW), moderate soil drying (MD), and severe soil drying (SD) were imposed during meiosis. MD significantly decreased spikelet degeneration in comparison with WW, due mainly to the alleviation in oxidative damage via enhancing ascorbate-glutathione (AsA-GSH) cycle activity in young panicles, and SD exhibited the opposite effects. Enhanced AsA-GSH cycle strength, decreased oxidative stress, and spikelet degeneration rate were closely associated with the synergistically elevated BR and ABA levels in young panicles in MD. In contrast, low BR and excessive ABA levels led to an increase in spikelet degeneration in SD. The three cultivars exhibited the same tendencies. The intrinsic link among AsA-GSH cycle, oxidative stress, spikelet degeneration rate, and BR and ABA levels was further verified by using transgenic rice lines and chemical regulators. BRs or ABA play a unique role in regulating spikelet degeneration. Synergistically increased BR and ABA levels in MD could work together to strengthen AsA-GSH cycle activity, leading to a reduction in oxidative damage and spikelet degeneration. On the other hand, a severe imbalance between low BR and excessive ABA levels may have contributed to the opposite effects in SD. Enhanced brassinosteroid (BR) and abscisic acid (ABA) levels in a moderate soil-drying regime during meiosis can synergistically suppress spikelet degeneration in rice, whereas a severe imbalance between low BR and excessive ABA levels in a severe soil-drying regime leads to an increase in spikelet degeneration.