Salt stress reduces the yield and quality of rice. It is of great significance to screen out salt-tolerant varieties for the development and utilization of saline land. The study was carried out on 114 rice varieties; first, seven varieties were selected and treated with different salt concentrations (0, 50, 85, 120, 155, 190, 225 mM), and seven traits, including germination energy, germination capacity, shoot length, root length, root number, plant fresh weight, and seedling vigor index, were measured. The salt concentration at which the sodium chloride injury index was 50% of the control was considered the optimal salt concentration. Second, 114 rice germplasms were carried out under an optimal salt concentration (120 mM). Then, principal component analysis, fuzzy function analysis, stepwise regression analysis, correlation analysis, and systematic cluster analysis were carried out on each parameter. There was a significant correlation between each parameter and the D-value, and the correlation coefficient between the seedling vigor index and D-value was the highest. D-value = − 0.272 + 1.335 × STI − SVI + 0.549 × STI − RN − 0.617 × STI-RL + 0.073 × STI − GE, R² = 0.986. Using this equation, the sodium chloride tolerance of rice in the germination experiment could be quickly identified. This study showed that the seedling vigor index was a reliable parameter to identify the salinity tolerance of rice varieties. Five groups were obtained by classification at a Euclidean distance of 5. There were 8 highly salt-tolerant cultivars, 23 salt-tolerant cultivars, 42 cultivars with moderate salt tolerance, 33 salt-sensitive cultivars, and 8 highly salt-sensitive cultivars. In this study, we found that Riguang was the most salt-tolerant rice variety, and Xiangxuejing15 was the most salt-sensitive variety.

Methyl jasmonate (MeJA) is a potent player that fine-tunes growth and developmental activities under salinity stress. In this study, we investigated the influence of MeJA on two rice cultivars (NJ9108 and XD22) subjected to different salinity stresses. Following stress treatment, reduction in the water use efficiency, relative water contents, and membrane stability index in both cultivars were observed, whereas MeJA treatment partially alleviated the negative effects. MeJA treatment significantly increased the maximum photochemical efficiency (Fv/Fm) and electron transfer to photosystem II (Fv/Fo). Under salinity stress, MeJA treatment significantly triggered the H₂O₂ and APX accumulation, while POD and SOD remained unchanged in both cultivars. Salt stress increased Na⁺ concentration in the roots and leaves but decreased K⁺ concentration and the K⁺/Na⁺ ratio in both cultivars. However, MeJA-treated plants had the maximum K⁺ accumulation in both leaves and roots under saline conditions. The differential expression pattern of OsHKT and OsHAK genes implied that ion homeostasis is crucial to growth under salt stress. These findings suggest that the application of MeJA can be an alternative source of reducing salinity without compromising growth and yield.

The high-affinity potassium transporter (HKT) genes are key ions transporters, regulating the plant response to salt stress via sodium (Na⁺) and potassium (K⁺) homeostasis. The main goal of this research was to find and understand the HKT genes in rice and their potential biological activities in response to brassinosteroids (BRs), jasmonic acid (JA), seawater, and NaCl stress. The in silico analyses of seven OsHKT genes involved their evolutionary tree, gene structures, conserved motifs, and chemical properties, highlighting the key aspects of OsHKT genes. The Gene Ontology (GO) analysis of HKT genes revealed their roles in growth and stress responses. Promoter analysis showed that the majority of the HKT genes participate in abiotic stress responses. Tissue-specific expression analysis showed higher transcriptional activity of OsHKT genes in roots and leaves. Under NaCl, BR, and JA application, OsHKT1 was expressed differentially in roots and shoots. Similarly, the induced expression pattern of OsHKT1 was recorded in the seawater resistant (SWR) cultivar. Additionally, the Na⁺ to K⁺ ratio under different concentrations of NaCl stress has been evaluated. Our data highlighted the important role of the OsHKT gene family in regulating the JA and BR mediated rice salinity tolerance and could be useful for rice future breeding programs.

Previous researchers have focused on the role of 24-epibrassnolide (EBR) in alleviating stresses in plants, whereas the effect of EBR on rice grain yield formation from the perspective of the whole growth stage remains less concerned. To further confirm the optimal application concentration and application periods of EBR in rice (Oryza sativa L.) under salt stress, a seed germination experiment, a seedling experiment, and a pot experiment were designed and conducted. Results showed that EBR treatment significantly enhanced germination indicators and seedling morphological traits, and the effects varied among different EBR concentrations, which were 0.5 > 1.0 > 0.1 > 0.05 mg L⁻¹. Under 0.5% salt treatments, 0.5 mg L⁻¹ EBR spraying significantly enhanced the seedling height, root length, above-/under-ground fresh weight, and above-/under-ground dry weight by 9.2%, 15.9%, 48.0%, 19.5%, 29.3%, and 12.5%, respectively. The spraying of EBR at different periods enhanced rice yield by 6.7% to 94.4% under salt stress. The relatively higher panicle number (increased by 42.9%) and spikelet number per panicle (increased by 96.1%) were the main reason resulting in higher grain yield under the S+T5 (EBR sprayed at both transplanting and heading stage) treatment. Compared to those under S treatment, catalase (CAT) activity was significantly enhanced by 25.0%, while malondialdehyde (MDA) content was dramatically decreased by 37.3% under the S+T5 treatment. The S+T5 treatment significantly enhanced the K⁺ content in rice root and leaf and decreased the Na⁺ content in rice root (by 30.4%), thereby leading to higher K⁺/Na⁺ under salt stress. The current study concluded that 0.5 mg L⁻¹ was the optimal concentration of EBR in alleviating the adverse effect of salinity. Spraying (transplanting + heading) of EBR twice displayed the best alleviating effect under salt stress, which was realized through enhanced antioxidant enzyme, higher K⁺ maintenance in leaves, and lowered absorption of Na⁺ in rice root.

This study aimed to assess global trends in research on salt stress in rice and provide new directions for future studies. The subjects in this study are a plain text file with full records and cited references (Web of Science core collection as the database, “rice” and “salt” as the retrieved title with the date range from 1 January 2000 to 31 December 2021). The bibliometric method was used in this study, and the results were visualized using Scimago Graphica, VOSviewer, and CiteSpace. The results showed that China, India, and Japan contributed most of the literature in this field, and the institutes with the largest academic output were the Chinese Academy of Science, the International Rice Research Institute, and Nanjing Agriculture University. This study argues that research on salt stress in rice has been conducted in three main areas: phenotypes, response mechanisms, and remediation strategies. Inoculation of rhizosphere bacteria, ion homeostasis, soil remediation, and gene editing will be popular topics in rice salt stress research in the future. This study aimed to provide a potential theoretical direction for research on salt stress in rice as well as a reference for feasible studies on the exploitation of saline–alkali lands.