Field-based trials and genotype evaluation until yielding stage are two important steps in improving the salt tolerance of crop genotypes and identifying what parameters can be strong candidates for the better understanding of salt tolerance mechanisms in different genotypes. In this study, the salt tolerance of 18 bread wheat genotypes was evaluated under natural saline field conditions and at three saline irrigation levels (5.25, 8.35, and 11.12 dS m⁻¹) extracted from wells. Multidimensional evaluation for salt tolerance of these genotypes was done using a set of agronomic and physio-biochemical attributes. Based on yield index under three salinity levels, the genotypes were classified into four groups ranging from salt-tolerant to salt-sensitive genotypes. The salt-tolerant genotypes exhibited values of total chlorophyll, gas exchange (net photosynthetic rate, transpiration rate, and stomatal conductance), water relation (relative water content and membrane stability index), nonenzymatic osmolytes (soluble sugar, free proline, and ascorbic acid), antioxidant enzyme activities (superoxide dismutase, catalase, and peroxidase), K⁺ content, and K⁺/Na⁺ ratio that were greater than those of salt-sensitive genotypes. Additionally, the salt-tolerant genotypes consistently exhibited good control of Na⁺ and Cl⁻ levels and maintained lower contents of malondialdehyde and electrolyte leakage under high salinity level, compared with the salt-sensitive genotypes. Several physio-biochemical parameters showed highly positive associations with grain yield and its components, whereas negative association was observed in other parameters. Accordingly, these physio-biochemical parameters can be used as individual or complementary screening criteria for evaluating salt tolerance and improvement of bread wheat genotypes under natural saline field conditions.

Salinity is a major abiotic stress that poses great obstacles to wheat production, especially in arid regions. The application of exogenous substances can enhance plant salt tolerance and increase its productivity under salinity stress. This work aimed to assess the mechanisms of selenium (Se) at different concentrations (2, 4 and 8 μM SeCl₂) to mitigate hazardous impacts of salt toxicity at physiological, biochemical and agronomic levels in bread wheat. The results displayed that Se foliar application increased chlorophyll content, net photosynthetic rate, transpiration rate, stomatal conductance, relative water content, membrane stability index, excised leaf water retention, proline, total soluble sugars, Ca content, K content, antioxidant enzyme activities and non-enzymatic antioxidant compounds compared to untreated plants. On the other hand, Se application decreased the content of Na, hydrogen peroxide and superoxide contents. Accordingly, our findings recommend exogenous Se application (in particular 8 μM) to alleviate the deleterious effects induced by salinity stress and improve wheat yield attributes through enhancing antioxidant defense systems and photosynthetic capacity.

The influence of 24-epibrassinolide (EBR₂₄), applied to leaves at a concentration of 5 μM, on plant physio-biochemistry and its reflection on crop water productivity (CWP) and other agronomic traits of six maize hybrids was field-evaluated under semi-arid conditions. Two levels of irrigation water deficiency (IWD) (moderate and severe droughts; 6000 and 3000 m³ water ha⁻¹, respectively) were applied versus a control (well-watering; 9000 m³ water ha⁻¹). IWD reduced the relative water content, membrane stability index, photosynthetic efficiency, stomatal conductance, and rates of transpiration and net photosynthesis. Conversely, antioxidant enzyme activities and osmolyte contents were significantly increased as a result of the increased malondialdehyde content and electrolyte leakage compared to the control. These negative influences of IWD led to a reduction in CWP and grain yield-related traits. However, EBR₂₄ detoxified the IWD stress effects and enhanced all the above-mentioned parameters. The evaluated hybrids varied in drought tolerance; Giza-168 was the best under moderate drought, while Fine-276 was the best under severe drought. Under IWD, certain physiological traits exhibited a highly positive association with yield and yield-contributing traits or CWP. Thus, exogenously using EBR₂₄ for these hybrids could be an effective approach to improve plant and water productivity under reduced available water in semi-arid environments.

Salinity is widespread environmental stress that poses great obstacles to rapeseed development and growth. Polyamines are key plant growth regulators that play a pivotal role in regulating salt tolerance. Rapeseed (Brassica napus L.) seedlings were treated by spermine (Spm) and spermidine (Spd) versus untreated control under salt stress conditions. It was detected that the Spd-treated plants had significantly elevated chlorophyll and proline content and maintained higher photosystem II (PSII) activity than those treated with Spm as well as untreated control under salt-stressed conditions. Similarly, Spd alleviated the devastating effects of NaCl stress on CO₂ assimilation and significantly elevated Rubisco activity (ribulose 1,5-bisphosphate carboxylase/oxygenase). The application of Spd also enhanced the activities of different antioxidant enzymes under NaCl stress. It modulated their respective transcription levels, including ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), and dehydroascorbate reductase (DHAR). In addition, exogenously sprayed Spd enhanced the polyamine pathway as observed by upregulated transcription of polyamine oxidase (PAO) and diamine oxidase (DAO). The Spd application enhanced expressions of Calvin cycle enzyme related genes such as Rubisco small subunit, Rubisco large subunit, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), 3-phosphoglyceric acid kinase (PGK), triose-3-phosphate isomerase (TPI), fructose-1,6-bisphosphate aldolase (FBA), sedoheptulose-1,7-bisphosphatase (SBPase), and fructose-1,6-bisphosphate phosphatase (FBPase). Consequently, this study demonstrates that exogenous application of Spd has a valuable role in regulating antioxidant enzyme activity, polyamine pathway, and Calvin cycle enzyme-related genes to alleviate salt stress damage in the plants.