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.

The objective of this study was to evaluate the applicability of soil pH and chlorophyll content as predictive indicators of damage in paddy fields affected by HCl spills, based on causal relationships. Five doses of HCl (e.g., 1, 50, 100, 200, and 500-fold of PNEC) were added to the paddy mesocosm during the rice heading stage. In the 7th week after the acid addition, rice grain quality (e.g., 1000-grain weight and filled grain ratio), soil microbial diversity (e.g., Operational Taxonomic Units (OTUs) and Shannon index), and soluble nutrients (e.g., NH4+, NO3-, SiO2, P2O5, and basic cations) were measured. Causal relationships among variables were analyzed using the Partial Least Square Path Model (PLS-PM). At the dose of 500xPNEC, all rice plants lodged when pH < 4. At 100xPNEC and 200xPNEC, the number of immature grains increased, resulting in a reduction in grain quality of over 18%. At 200xPNEC, the microbial OTUs and the Shannon index decreased by 30%. Notably, the proportion of Planctomycetes, the dominant phylum in the control soil, decreased. The reduction of Planctomycetes led to excessive NH4+ accumulation in the soil, which leads to an undesirable increase of chlorophyll content thereby deteriorating grain quality. The causal relationship suggests that information of soil pH and leaf chlorophyll can aid us in predicting damage for grain quality and microbial diversity.

The rice root-knot nematode, Meloidogyne graminicola, is the major bottleneck in aerobic and direct-seeded rice cultivation. Host plant resistance is an environmentally-friendly and cost-effective approach to mitigate damage caused by M. graminicola. Considering the limited availability of genetic resources in Asian rice (Oryza sativa) cultivars, exploration of novel sources of resistance to M. graminicola is necessary. In the present study, we screened 192 diverse wild rice accessions from nine species (Oryza longistaminata, O. barthii, O. glaberrima, O. meridionalis, O. nivara, O. punctata, O. officinalis, O. glumaepatula and O. rufipogon) to identify sources of resistance to M. graminicola. Based on gall number and multiplication factor, two immune and 25 resistant accessions were identified. 'Pusa Basmati 1121' and 'W-27-1' displayed the highest number of galls per root system and multiplication factor, whereas 'NW-1' and 'NW-17' had the lowest. Further examination of nematode development suggested that M. graminicola penetrated less often into highly resistant varieties, and, if they penetrated, the juveniles failed to develop into females. Multi-variate analysis was used to investigate the diversity among the wild rice accession for M. graminicola resistance. Analyses showed that the 192 wild accessions of rice could be divided into six clusters based upon their resistance levels. Thirty-four wild accessions exhibited high resistance to M. graminicola, while most accessions showed susceptibility. Analysis of 49 resistant accessions in soil assay correlated very strongly with the identical accessions in 'PF-127' assay using the same parameters, indicating the high reproducibility of 'PF-127'based assay. The resistant accessions identified in the current study would be a useful resource for studying genetics and the mechanism of resistance to M. graminicola.

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.

Toxicity due to excess iron can result in oxidative stress, impacting photosynthetic processes, particularly those related to the electron transport chain and CO2 assimilation. The present study investigated how oxidative damage caused by excess iron affects the hydraulic and diffusive traits and the photobiochemistry of two contrasting rice cultivars regarding their iron sensitivity. Two rice cultivars, IRGA 424 (tolerant to excess iron) and IRGA 417 (sensitive to excess iron), in V6 growth stage were submitted to four concentrations of Fe2+ (0.019 control, 2, 4, and 7 mM) in nutrient solution for 8 days. Excess Fe associated with oxidative damage in the roots decreased the leaf water potential and the root xylem sap flow in both cultivars. The tolerant cultivar IRGA 424 exhibited increased photosynthetic efficiency with a longer exposure but did not change carboxylation efficiency and stomatal conductance up to 2 mM of Fe. The sensitive cultivar experienced greater oxidative damage, which may have contributed to decreased quantum yields, specific efficiencies, and energy fluxes of PSII, thereby increasing photoinhibitory processes. Photoprotective mechanisms and antioxidant enzymes were more efficient in the tolerant cultivar IRGA 424 than in the sensitive cultivar with increased Fe concentrations. The sensitivity of rice to excess iron was associated with the inability to prevent oxidative damage in the roots, with constraints in root xylem sap flow, and with limitations in stomatal function and photobiochemical processes. This knowledge could support the development of iron-tolerant rice cultivars, contributing to increased productivity in soils with excess Fe.

The P-MFC technology, which acts as an energy source, is one of the promising methods to reduce environmental pollution. In the present study, the P-MFC was constructed using Oryza sativa (Paddy plant), and various electrode materials like carbon, copper, and titanium oxide were used as cathode and aluminum as anode. The experiment was carried out for 34 days. The plant growth was periodically observed and measured, significantly increasing to produce electricity. The highest growth rate was recorded as 52 +/- 1.20 cm whereas the power output varies between P-MFCs. The maximum output voltage was obtained as 1320 +/- 230 mV in the copper- based P-MFC. The voltage disparity in PMFCs stipulates using different electrode materials in P-MFC systems resulting in assorted competence of electricity production. The analysis of the plant roots after the experiment revealed increased concentration of amino acid and carbohydrate. According to the correlation analysis, the plant growth was indistinguishable from agricultural field plants, which indicates that P-MFC installation does not cause any crop damage. Available Microbial load on electrode material and rhizospheric soil resembles bacterial population-induced power generation. This study demonstrated that P-MFCs with paddy plants and copper electrode are a favorable and assured application for future potential electricity production.

Main conclusionRhizobacteria and silicon fertilization synergism suppress leaf and panicle Blast, and mitigates biotic stress in rice plants.AbstractAssociation of bioagents and silicon is synergistic for mitigating leaf and panicle blast and low phosphorus (P) levels in upland rice, under greenhouse conditions. This study aimed to evaluate the potential of the bioagents and silicon interaction on blast disease severity suppression in upland rice plants, under field low P conditions. The experiment was conducted during two growing seasons (E1 and E2), in randomized block design with four replications, and consisted of five treatments, combining a mix of three rhizobacteria, BRM 32114 and BRM62523 (Serratia marcescens), and BRM32110 (Bacillus toyonensis), and three application methods (seed treatment, drenching, spraying). Calcium and magnesium silicate (2 t/ha) was applied over a low soil P, 30 days before sowing. Leaf blast (LBS) and panicle blast (PBS), area under the disease progress curve (AUDPC), activity of enzymes related to oxidative stress, pathogenesis-related (PR), biochemical indicators such as hydrogen peroxide, chlorophyll a and b, carotenoids, and grain yield (GY), were assessed. Bioagents and silicon suppressed LBS by 77.93 and PBS by 62.37%, reduced AUDPC by 77.3 (LBS) and 60.6% (PBS). The yield in E1 was 25% higher than in E2. The treatments statistically differ only in E2, the yield with bioagents and silicon (2435.72 kg ha-1) was 71.95% higher compared to the absolute control. All enzymatic activities related to oxidative stress and PR proteins were modulated by bioagents and silicon association. The association of rhizobacteria and silicon exhibited a synergistic effect, and represents a bioprotective combination to reduce the effects of different stresses and indirectly reduces the use of chemical inputs.

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.

Antioxidant complex enzymes have a significant role in cellular homeostasis control in plants, and they inhibit the toxic action of reactive oxygen species when they are in excess. There are many antioxidant enzymes executing this role; among these, superoxide dismutase, catalase, and ascorbate peroxidase are reported as the most studied in this process, as they prevent free radicals from becoming more reactive and toxic to cells. Thus, this research was conducted to evaluate antioxidant enzyme expression in response to hydric stress at the reproductive stage in upland rice genotypes. Three genotypes from the upland rice breeding program on agreement between UFLA, EPAMIG, and EMBRAPA, CMG2093, CMG2172, and BRSMG Relampago, were used as controls. Genotypes were grown under field conditions with supplementary irrigation during the whole crop cycle, and hydric stress was induced in the reproductive phase before panicle emission. Seedlings were used in enzyme analyses from the emergence test and IVE on substrate (soil+sand at a 2:1 rate) at 70% and 10% field capacity. Significant differences were observed among genotypes for vigor tests. In biochemical tests, the CMG2093 genotype had lower damage on hydric deficit, with the best performance under hydric restriction conditions, being considered tolerant for this stress type.

Hydropriming rice seeds effectively improve the germination percentage, shortens the germination period, and promotes seedling growth. The impact of seed hydropriming is to speed up growth under dry soil conditions, thereby avoiding drought damage. This study analyzes the effect of hydropriming on morpho-physiological changes in the water uptake of rice seeds using Kasalath and Nipponbare under water-deficit conditions. Upon exposure to osmotic stress, both varieties showed delays in the time to reach germination. In addition, all germination phases exhibited reductions in the activity of alpha-amylase and total soluble sugar by osmotic stress; however, in all germination phases of the hydroprimed seeds, the activity and contents of those were significantly increased, resulting in increased size of the coleoptile, plumule, and radicle. In hydroprimed seeds, Kasalath was superior to Nipponbare in the ratio of the water-deficit-to-well-watered conditions for all traits related to germination, which may have been attributable to hydropriming having a greater effect on Kasalath. Interestingly, Primed Kasalath had a lower level of alpha-amylase, despite the having a higher content of total soluble sugars than primed Nipponbare.