Alleviating Salinity Stress Research Articles

Bacterial endophyte mediated plant tolerance to salinity: growth responses and mechanisms of action.

Salinity stress is one of the key constraints for sustainable crop production. It has gained immense importance in the backdrop of climate change induced imbalanced terrestrial water budgets. The traditional agronomic approaches and breeding salt-tolerant genotypes have often proved insufficient to alleviate salinity stress. Newer approaches like the use of bacterial endophytes associated with agricultural crops have occupied center place recently, owing to their advantageous role in improving crop growth, health and yield. Research evidences have revealed that bacterial endophytes can promote plant growth by accelerating availability of mineral nutrients, helping in production of phytohormones, siderophores, and enzymes, and also by activating systemic resistance against insect pest and pathogens in plants. These research developments have opened an innovative boulevard in agriculture for capitalizing bacterial endophytes, single species or consortium, to enhance plant salt tolerance capabilities, and ultimately lead to translational refinement of crop-production business under salty environments. This article reviews the latest research progress on the identification and functional characterization of salt tolerant endophytic bacteria and illustrates various mechanisms triggered by them for plant growth promotion under saline environment.

Seed priming alleviated salinity stress during germination and emergence of wheat (Triticum aestivum L.)

Seed priming is known to often alleviate salinity stress during seed emergence and subsequent crop growth. This study compares the effects of salinity stress on the germination and emergence of wheat (Triticum aestivum L.) seeds untreated (control) and primed with ascorbic acid (Asc), potassium silicate (K2SiO3), proline (Pro), spermidine (Spd) and Lake Urmia saline water (LUsw). Saline water from Lake Urmia (Iran) was diluted to produce salinities with electrical conductivities (EC) of 2, 4, 6, 8, 10, 12, 14, 20 dS m−1, while distilled water (EC ≈ 0 dS m−1) was used for the control. Two independent sets of experiments were conducted. The first experiments were used to select the most effective concentration of each priming agent based on the final germination percentage (GP) and germination rate (GR). The second set of experiments aimed to analyze the measured data in terms of salinity response functions in order to quantitatively determine the most effective priming agent(s). The first experiments showed that the most effective concentrations of Spd (0.5 mM), Pro (25 mM), K2SiO3 (1.5 mM) and LUsw (100 mg L−1) mitigated the negative impacts of salinity on GR by 32, 18, 17 and 22 %, respectively. The second experiment showed that the Maas and Hoffman (1977) and van Genuchten and Hoffman (1984) salinity response functions provided effective descriptions of seedling and early growth response to salinity stress. Mean values of the salinity threshold (EC*) and the salinity at which a given trait was reduced by 50 percent (EC50) in these functions were 3.4 and 10.8 dS m−1 for the control, respectively. By comparison, the EC* values for the K2SiO3, Pro, Spd and LUsw primed seeds were 5.3, 4.5, 4.7, and 4.2 dS m−1, respectively, and the EC50 values were 12.4, 11.4, 11.9, and 9.4 dS m−1, respectively. The beneficial effects of K2SiO3 on seedling growth were more evident than those of the other priming agents. K2SiO3 had the highest effect on EC* and EC50 of the vitality index (VI), showing increases of 151 and 34 %, respectively. The highest increases of EC* and EC50 for seedling dry weight (72 and 24 %, respectively) were obtained with Spd and K2SiO3. The findings provide much insight on relieving the negative effects of salinity through cost-effective seed priming operations so as to improve the production of wheat under saline conditions.

Salinity Stress Alleviation by Foliar Bio-Stimulant, Proline and Potassium Nutrition Promotes Growth and Yield Quality of Garlic Plant

Soil salinity is one of the major yield-limiting factors for crop production in many agricultural regions all over the world. Besides following efficient management practices at the field scale to reduce accumulation of salts in the effective root-zone, the effective use of treatments to alleviate the effects of salinity stress and improve crop salt tolerance is a promising solution to ensure crop production in such adverse conditions. A field experiment was carried out to investigate the effect of foliar spray with plant-based biostimulant (i.e. with and/or without 3% yeast extract), three levels of proline (0, 25, and 50 mM), and combined with potassium fertilizers, as potassium sulfate, 48% K2O (0, 50, and 100 kg/fed.) on growth promotion, chemical composition of garlic leaves, bulb quality parameters as well as yield and its components of garlic plant grown under moderate saline soil. Results revealed that the interaction between foliar spray with yeast extract at 3% and proline at 50 mM combined with proper K level at 100 kg/fed., was the best interaction treatment for increasing vegetative growth parameters, i.e. plant height, number of leaves per plant, and mineral contents (N, P, K, S, Ca and Mg in leaves), and proline content of garlic leaves after 135 days from planting time, total yield/fed., and garlic yield quality parameters at harvesting time. In conclusion, the detrimental effects of salinity stress can be alleviated by stress tolerance-inducing compounds, such as yeast extract and proline with proper application rate of K fertilization during the growing season of garlic crop.

Potassium induced metabolic changes with or without NaCl salinity in maize plants growing in aridlands

This study aimed to determine whether the application of different potassium salts (KCl, K2SO4, KNO3, KH2PO4) can alleviate the NaCl induced salinity in maize plants. NaCl stress decreased maize morphological parameters versus the control. NaCl combined with different type of potassium supplements were not significantly increased the root and stem length versus treatments with NaCl. However, a decrease in chlorophyll 'a', 'b', and total chlorophyll concentrations have been noted in the NaCl stressed plants when compared to control. The chlorophyll content rose with age in the leaves of control and treated plants. When compared to NaCl stressed plants, the chlorophyll content was higher in the NaCl with different types of potassium. Proline content increase in Maize plants under treatment with NaCl when compared to the control. To provide stress protection, several types of potassium are added along with NaCl to further reduce the proline concentration. Compared to the control, the phenol content of Maize plants treated with NaCl marginally increased. The phenol concentration was further raised by the addition of various potassium types along with NaCl, providing additional stress protection. The present study; therefore, suggests that exogenous potassium salts confers tolerance to salt stress to maize plants and have a significant role in partial alleviation of salinity stress especially in arid and semi-arid regions. Keywords: salinity, potassium salt, alleviation, biochemical, pigments

Silicon Mediated Alleviation of Salinity Stress Regulated by Silicon Transporter Genes (Lsi1 and Lsi2) in Indica Rice

Silicon accumulation is known to improve tolerance of plants under both biotic and abiotic stress. Salinity stress is an inevitable crisis causing wide spread damage to rice leading to food insecurity. The influence of Si (1mM) on two rice cultivars cv. Ghanteswari (high accumulator) and cv.Badami (low accumulator) which differs in Si uptake potential under saline (10ds/m EC) and non- saline conditions were studied in nutrient culture. The Si transporter genes were isolated and characterized to determine their function in salinity tolerance. Under stress, there was an increase in Si accumulation, Na+/K+ ratio, electrolyte leakage, lipid peroxidation and antioxidant activities. On addition of silicon, the K+ uptake increased, membrane damage reduced and osmolytes balance improve under salinity. But, the level of resurgence was varied in both cultivars, due to their differential Si-accumulation. Molecular characterizations of Lsi1 protein revealed its involvement in the movement of ion and water and therefore prevent osmotic stress. The Lsi2 is responsible for removal of Na+, reducing salt toxicity. Silicon accumulation is responsible for maintenance of cell water status, osmotic balance and Na+ ion exclusion during high salinity. The variable relative expression of Lsi2 provides a possible explanation for differential genotypic uptake of silicon.

Nitrogen management enhanced plant growth, antioxidant ability, and grain yield of rice under salinity stress

AbstractSalinity is a major abiotic stress limiting crop growth and reducing grain yield. In recent years, little progress was made in salt‐tolerant cultivation techniques. Therefore, a controlled experiment was conducted to study the effects of nitrogen management (NM) on growth, antioxidant ability, and yield performance of salt‐tolerant rice (Oryza sativa L.) under salinity stress. Three salinity levels (0‰ as control; 0.75‰, 4.3 dS m−1; and 1.5‰, 7.7 dS m−1) and four levels of NM (tillering fertilizer/panicle initiation fertilizer = 7:3, 6:4, 5:5, and 4:6) were arranged in this study. Under salinity stress, plant height, tiller number, fresh weight, grain yield, panicle, spikelets per panicle, grain weight, and soluble sugar content in stem were significantly decreased. In contrast, antioxidant parameters of superoxide dismutase, peroxidase, and catalase were significantly increased. Grain filling percentage and sucrose content were slightly changed. Compared to the control, grain yield was reduced by 45.6%, 34.8%, 60.4%, and 46.7% at the ratio of 7:3, 6:4, 5:5, and 4:6 NM at 0.75‰ salinity level, and 73.5%, 59.7%, 74.8%, and 61.7% at 1.5‰ salinity level, respectively. The highest yield was generated by 6:4 NM at both the 0.75‰ and 1.5‰ salinity level, and the lowest by 4:6 and 5:5. However, NM could obviously alleviate the inhibition effects of salinity stress and improve antioxidant ability of rice. Among them, 6:4 NM performed the best alleviation effects, followed by 7:3 and 5:5 NM. This study suggests that the appropriate NM can effectively alleviate salinity stress and increase grain yield.

Treatment of Sweet Pepper with Stress Tolerance-Inducing Compounds Alleviates Salinity Stress Oxidative Damage by Mediating the Physio-Biochemical Activities and Antioxidant Systems

Salinity stress occurs due to the accumulation of high levels of salts in soil, which ultimately leads to the impairment of plant growth and crop loss. Stress tolerance-inducing compounds have a remarkable ability to improve growth and minimize the effects of salinity stress without negatively affecting the environment by controlling the physiological and molecular activities in plants. Two pot experiments were carried out in 2017 and 2018 to study the influence of salicylic acid (1 mM), yeast extract (6 g L−1), and proline (10 mM) on the physiological and biochemical parameters of sweet pepper plants under saline conditions (2000 and 4000 ppm). The results showed that salt stress led to decreasing the chlorophyll content, relative water content, and fruit yields, whereas electrolyte leakage, malondialdehyde (MDA), proline concentration, reactive oxygen species (ROS), and the activities of antioxidant enzymes increased in salt-stressed plants. The application of salicylic acid (1 mM), yeast extract (6 g L−1), and proline (10 mM) markedly improved the physiological characteristics and fruit yields of salt-stressed plants compared with untreated stressed plants. A significant reduction in electrolyte leakage, MDA, and ROS was also recorded for all treatments. In conclusion, our results reveal the important role of proline, SA, and yeast extracts in enhancing sweet pepper growth and tolerance to salinity stress via modulation of the physiological parameters and antioxidants machinery. Interestingly, proline proved to be the best treatment.

Treatment of Sweet Pepper with Stress Tolerance-Inducing Compounds Alleviates Salinity Stress Oxidative Damage by Mediating the Physio-Biochemical Activities and Antioxidant Systems

Salinity stress occurs due to the accumulation of high levels of salts in soil, which ultimately leads to the impairment of plant growth and crop loss. Stress tolerance-inducing compounds have a remarkable ability to improve growth and minimize the effects of salinity stress without negatively affecting the environment by controlling the physiological and molecular activities in plants. Two pot experiments were carried out in 2017 and 2018 to study the influence of salicylic acid (1 mM), yeast extract (6 g L−1), and proline (10 mM) on the physiological and biochemical parameters of sweet pepper plants under saline conditions (2000 and 4000 ppm). The results showed that salt stress led to decreasing the chlorophyll content, relative water content, and fruit yields, whereas electrolyte leakage, malondialdehyde (MDA), proline concentration, reactive oxygen species (ROS), and the activities of antioxidant enzymes increased in salt-stressed plants. The application of salicylic acid (1 mM), yeast extract (6 g L−1), and proline (10 mM) markedly improved the physiological characteristics and fruit yields of salt-stressed plants compared with untreated stressed plants. A significant reduction in electrolyte leakage, MDA, and ROS was also recorded for all treatments. In conclusion, our results reveal the important role of proline, SA, and yeast extracts in enhancing sweet pepper growth and tolerance to salinity stress via modulation of the physiological parameters and antioxidants machinery. Interestingly, proline proved to be the best treatment.

Alleviation of Salinity Stress in Maize Using Silicon Nutrition

Improving salinity tolerance through mineral nutrition in plants is emerging strategy for sustainable agriculture under limited resources. Silicon (Si) is considered as silver bullet to mitigate biotic and abiotic stresses. Present study was conducted to understand the new mechanisms of Si nutrition against salinity stress in two different maize (Zea mays L.) cultivars (‘Syngenta-8441’ and ‘Pearl’). Three different levels of NaCl (0.67, 8 and 13 dSm-1) were used with and without addition of silicic acid (2 mM). Distilled water was used for irrigation purposes and crop was harvested after 40 days of post germination. Results indicated that plant biomass reduced under saline condition while Si application increased growth parameters. Data regarding chemical analysis showed that Si nutrition reduced Na+ concentration and enhanced K+ levels in root, shoot, new and old leaves of ‘Sygenta 8441’ compared to ‘Pearl’ maize variety. Si application improved both chlorophyll a and b in both maize cultivars compared to NaCl-treated plants. The current findings indicate that Si nutrition can alleviate salinity stress in maize without decreasing growth attributes of crop and ‘Sygenta 8441’ is a salt resistant variety whereas ‘Pearl’ is a salt sensitive variety.
 
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 In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue.
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NaCl induced oxidative stress in legume crops of Indian Thar Desert: an insight in the cytoprotective role of HO1, NO and antioxidants.

The manuscript highlights the role of antioxidants in alleviation of salinity stress in two principal legume crops Cyamopsis tetragonoloba and Vigna radiata of Indian Thar Desert. The study evaluates correlation between the antioxidants of two cultivars in terms of morphological and physiological alterations. Hydroponically acclimatized seedlings of both the crops were subjected to NaCl stress at different concentrations ranges from 10 to 100mM. After 96h, the treated legumes were harvested to analyze the cellular homeostasis and salt tolerance mechanism via examining growth, stress parameters, osmoprotectants and enzymatic antioxidants. Differential response in the antioxidants activity was observed in crops. Equal contribution of antioxidants in mitigation of salinity stress was recorded in C. tetragonoloba while V. radiata shows greater tolerance by accumulating greater amount of proline which is approximately 2.72 folds higher than C. tetragonoloba. Moreover, the NR and HO1 activities in V. radiata were recorded to be 2.76 and 1.55 folds respectively which is 1.2 times higher in comparison to C. tetragonoloba. The detrimental effect of NaCl in terms of MDA content was also higher in V. radiata which concluded that V. radiata is more reactive towards salinity stress than C. tetragonoloba. The study is significant as this is the first report illustrating the sensitivity and tolerance level of NaCl in legumes of Thar Desert.

Ameliorative effects of inoculation with Serratia marcescens and grafting on growth of eggplant seedlings under salt stress

Grafting on a moderate salt-tolerant rootstock (Vista-306) and bacteria (Serratia marcescens) inoculation were tested whether grafting and bacteria can alleviate salinity stress in eggplant. Two salt-tolerant eggplant genotypes (‘Mardin Kızıltepe’, ‘Burdur Merkez’) and two salt-sensitive eggplant genotypes (‘Artvin Hopa’, ‘Kemer’) were used as scions. Grafted and non-grafted seedlings with 4–5 true leaves were transferred to pots filled with a mixture of peat: perlite (2:1) in a controlled greenhouse and were cultivated under temperatures of 23–25 °C with approximately 50–55% relative humidity. After 10 days from planting, 20 mL bacteria solution (cell density of 3 × 108 cells mL−1) per plant was applied to the root region of the seedlings as inoculum. 200 mM NaCl solution was applied to plants for 20 days after 5 days from inoculation of the bacteria. The study was arranged in a randomized block factorial design with three replicates. The grafted seedlings induced salt tolerance registering lower foliar concentrations of Na+ and Cl–, the lower lipid peroxidation and higher antioxidative enzyme activities. Inoculation of the bacteria significantly counteracted the salt-induced adverse effects on growth characteristics, leaf Cl−, Na+ contents, and antioxidative enzyme activities. In conclusion, grafting and inoculation with Serratia marcescens are effective in improving growth and some key physiological processes in eggplant under salt stress.

Involvement of nitrate reductase-dependent nitric oxide production in magnetopriming-induced salt tolerance in soybean.

In the present study, experiments were performed to investigate the role of nitric oxide (NO) in magnetopriming-induced seed germination and early growth characteristics of soybean (Glycine max) seedlings under salt stress. The NO donor (sodium nitroprusside, SNP), NO scavenger (2-[4-carboxyphenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, CPTIO), inhibitors of nitrate reductase (sodium tungstate, ST) or NO synthase (N-nitro-L-Arg-methyl ester, LNAME) and NADPH oxidase inhibitor (diphenylene iodonium, DPI) have been used to measure the role of NO in the alleviation of salinity stress by static magnetic field (SMF of 200 mT, 1h). Salt stress (50 mM NaCl) significantly reduced germination and early growth of seedlings emerged from non-primed seeds. Pre-treatment of seeds with SMF positively stimulated the germination and consequently promoted the seedling growth. ST, LNAME, CPTIO and DPI significantly decreased the growth of seedling, activities of α-amylase, protease and nitrate reductase (NR), hydrogen peroxide (H2 O2 ), superoxide (O2 •- ) and NO content in roots of seedlings emerged from non-primed and SMF-primed seeds. However, the extent of reduction was higher with ST in seedlings of SMF-primed seeds under both conditions, whereas SNP promoted all the studied parameters. Moreover, the generation of NO was also confirmed microscopically using a membrane permanent fluorochrome (4-5-diaminofluorescein diacetate [DAF-2 DA]). Further, analysis showed that SMF enhanced the NR activity and triggered the NO production and NR was maximally decreased by ST as compared to LNAME, CPTIO and DPI. Thus, in addition to ROS, NO might be one of the important signaling molecules in magnetopriming-induced salt tolerance in soybean and NR may be responsible for SMF-triggered NO generation in roots of soybean.

Ameliorative Effects of Jasmonic Acid and Humic Acid on Antioxidant Enzymes and Salt Tolerance of Forage Sorghum under Salinity Conditions

Salinity is one of the most important factors that reduce the growth and antioxidant defense of plants. A controlled pot experiment was conducted to investigate the ameliorative effects of jasmonic acid (JA) priming (0, 5, and 10 mM) and humic acid (HA) (0, 3, and 6 g HA kg−1 soil) amendment on antioxidant enzymes and salt tolerance of forage sorghum seedling (Sorghum bicolor L.) grown under three salinity conditions (0, 100, and 200 mM NaCl). Salinity stress reduced emergence seedling index (ESI), promptness index (PI), emergence stress tolerance index (ESTI), dry weight stress tolerance index (DWSTI), and the activities of the peroxidase (POD) and catalase (CAT) enzymes. The activity of superoxide dismutase (SOD) and malondialdehyde (MDA) content increased with salinity. Application of JA positively affected all parameters except CAT and MDA. Humic acid significantly increased all measured parameters except ESTI, DWSTI, and SOD activity. At the 200 mM NaCl level, JA and HA increased CAT, POD, SOD, ESI, DWSTI, ESTI, PI, and MDA as compared with the control. The application of HA at 6 g kg−1 soil decreased SOD and ESI relative to the control at high salinity. The application of 10 mM JA combined with HA at 6 g kg−1 soil was most effective in alleviating salinity stress. Therefore, the combined application of JA and HA on forage sorghum may improve salt tolerance and increase antioxidant enzymes that alleviate damages caused by salinity stress.Core Ideas Application of jasmonic acid and humic acid (HA) mitigated salinity stress. Jasmonic acid (JA) and HA increased the antioxidant enzymes. Applying a combination of JA and HA at high levels of salinity improved salt tolerance.

Alleviation of salinity stress by hydrogen peroxide and nitric oxide in tomato plants

Salinity is one of the major abiotic stress factors limiting plant growth and productivity, particularly in arid and semi-arid climates. Hydrogen Peroxide (H2O2) and Nitric Oxide (NO) are important signaling molecules in plant response to abiotic stress. In this research the effects of foliar sprays with H2O2 (10 mM) and NO (0.1 mM sodium nitroprusside, as a NO donor) on alleviation of Salinity stress (0, 25, 50 and 100 mM NaCl) were investigated in Tomato (Solanum lycopersicum L. cv. Falat). Photosynthetic attributes, plant-water relations, membrane stability index and growth parameters were decreased by NaCl treatments. Exogenous H2O2 and NO application enhanced salt stress tolerance in tomato plants by improving the photosynthetic efficiency and plant water status as measured by relative water content and membrane stability index. These results were positively reflected by the increase in plant growth under salinity stress conditions. The results of this study described that under the adverse conditions of salinity stress, H2O2 and NO could activate the photosynthetic system and improve the physiological attributes in plant growth.

Halotolerant Rhizobacterial Strains Mitigate the Adverse Effects of NaCl Stress in Soybean Seedlings.

Background Salinity is one of the major abiotic constraints that hinder health and quality of crops. Conversely, halotolerant plant growth-promoting rhizospheric (PGPR) bacteria are considered biologically safe for alleviating salinity stress. Results We isolated halotolerant PGPR strains from the rhizospheric soil of Artemisia princeps, Chenopodium ficifolium, Echinochloa crus-galli, and Oenothera biennis plants; overall, 126 strains were isolated. The plant growth-promoting traits of these isolates were studied by inoculating them with the soil used to grow soybean plants under normal and salt stress (NaCl; 200 mM) conditions. The isolates identified as positive for growth-promoting activities were subjected to molecular identification. Out of 126 isolates, five strains—Arthrobacter woluwensis (AK1), Microbacterium oxydans (AK2), Arthrobacter aurescens (AK3), Bacillus megaterium (AK4), and Bacillus aryabhattai (AK5)—were identified to be highly tolerant to salt stress and demonstrated several plant growth-promoting traits like increased production of indole-3-acetic acid (IAA), gibberellin (GA), and siderophores and increased phosphate solubilization. These strains were inoculated in the soil of soybean plants grown under salt stress (NaCl; 200 mM) and various physiological and morphological parameters of plants were studied. The results showed that the microbial inoculation elevated the antioxidant (SOD and GSH) level and K+ uptake and reduced the Na+ ion concentration. Moreover, inoculation of these microbes significantly lowered the ABA level and increased plant growth attributes and chlorophyll content in soybean plants under 200 mM NaCl stress. The salt-tolerant gene GmST1 was highly expressed with the highest expression of 42.85% in AK1-treated plants, whereas the lowest expression observed was 13.46% in AK5-treated plants. Similarly, expression of the IAA regulating gene GmLAX3 was highly depleted in salt-stressed plants by 38.92%, which was upregulated from 11.26% to 43.13% upon inoculation with the microorganism. Conclusion Our results showed that the salt stress-resistant microorganism used in these experiments could be a potential biofertilizer to mitigate the detrimental effects of salt stress in plants via regulation of phytohormones and gene expression.

Calcium availability regulates antioxidant system, physio-biochemical activities and alleviates salinity stress mediated oxidative damage in soybean seedlings

Salinity is considered as one of the devastating abiotic stress factors and global climate change has further worsened the situation. Present experiments were aimed to evaluate the role of calcium (Ca) availability on growth and salinity tolerance mechanisms in soybean. Seedlings were grown with (2 mM Ca) and without Ca supplementation and modulation in key physiological and biochemical parameters were studied. Salinity (100 mM NaCl) stress resulted in growth reduction in terms of height and biomass accumulation, which was more pronounced in Ca-deficient plants. Relative to control (Ca deficient) and NaCl stressed plants, Ca supplemented seedlings exhibited higher relative water content, pigment synthesis and the photosynthetic efficiency. Ca availability affected the synthesis of proline, glycine betaine and soluble sugars under normal and saline growth conditions. Optimal Ca supplementation up-regulated the activities of antioxidant enzymes assayed and the contents of non-enzymatic antioxidants (ascorbate, glutathione, and tocopherol) thereby reflecting in amelioration of NaCl induced oxidative damage. Moreover, increased accumulation of phenols due to Ca supplementation and the amelioration of NaCl mediated decline if nitrate reductase activity was observed. More importantly, Ca availability reduced the accumulation of Na under control and NaCl stressed conditions restricting the damging effects on metabolism. Availability of optimal Ca potentially regulates the salinity tolerance mechanisms in soybean by maintaining osmoregulation and antioxidant metabolism.

Mechanisms of Silicon-Mediated Amelioration of Salt Stress in Plants.

Silicon (Si), the second most predominant element in the earth crust consists of numerous benefits to plant. Beneficial effect of Si has been apparently visible under both abiotic and biotic stress conditions in plants. Supplementation of Si improved physiology and yield on several important agricultural and horticultural crops. Salinity is one of the major abiotic stresses that affect growth and yield. The presence of high concentration of salt in growing medium causes oxidative, osmotic, and ionic stresses to plants. In extreme conditions salinity affects soil, ground water, and limits agricultural production. Si ameliorates salt stress in several plants. The Si mediated stress mitigation involves various regulatory mechanisms such as photosynthesis, detoxification of harmful reactive oxygen species using antioxidant and non-antioxidants, and proper nutrient management. In the present review, Si mediated alleviation of salinity stress in plants through the regulation of photosynthesis, root developmental changes, redox homeostasis equilibrium, and regulation of nutrients have been dealt in detail.

Alleviation of Salinity Stress on Some Growth Parameters of Wheat by Exopolysaccharide-Producing Bacteria

After isolation of halophilic bacteria from saline soils, the effects of two superior isolates producing exopolysaccharide TP7 and TP5 was investigated on some wheat growth parameters such as shoot and root dry weight and concentration of K+, Ca2+, Na+ and K+/Na+, Ca2+/Na+ ratios under saline stress. Inoculation with bacteria (TP7, TP5 and both of strains) had a positive effect on shoot weight (74.71, 57.52 and 82.45%) at EC 8 dS m−1 and (45.26, 60.95 and 71.28%) at EC 16 dS m−1. Also, TP7 and TP5 isolates can increase plant resistance to salt and drought stresses by decreasing Na+ uptake and in 16 dS m−1 led to an increase in dry weight of root in comparison with control by 97.95, 128.29 and 193.53%, respectively. In higher-salinity treatments, all of treatments (TP5, TP7 and both of strains) had a significant effect on K+ concentration, especially in EC 16 dS m−1 by 29.58, 45.94 and 53.56% and 35.50, 52.37 and 58.65% in water stress and non-water stress, respectively. The determination of 16S rRNA gene sequences of isolates TP7 and TP5 showed that they are mostly close to Bacillus subtilis susp. inaquosorum (98.49% sequence similarity) and Marinobacter lipolyticus SM19 (T) (97.69% sequence similarity), respectively. Generally, results showed that these isolates can be used as a tool for reducing adverse effects of salinity and drought stresses in wheat plant.

Mitigation of salinity stress in plants using plant growth promoting bacteria

Salinity is one of the major constraints prevailing in environment that affects not only plant growth but also agriculture productivity and soil fertility. Salinity stress causes nutritional and hormonal imbalance, ion toxicity, oxidative and osmotic stress and increased susceptibility of plant to diseases. Increasing use of chemical based fertilizers creates demand for environmental friendly and ecological compatible alternative in agriculture. Plant growth promoting bacteria (PGPB) have tremendous ability to mitigate salinity stress and ameliorate plant growth, playing vital role in food security by increasing agriculture crop productivity. PGPB inoculation under salinity promotes plant growth by several traits including 1-aminocyclopropane 1 carboxylate (ACC) deaminase activity, synthesis of plant hormones (such as indole acetic acid (IAA), gibberellic acid (GA), abscisic acid (ABA), cytokinin) and exopolysaccharides. PGPB alleviates salinity stress in plants by providing nutrients, maintaining high potassium and sodium ratio, increasing accumulation of osmolytes, enhanced photosynthesis and activity of antioxidant enzymes. The present review highlights and discusses current knowledge on effect of salinity stress on plant growth, PGPB mechanisms resulting in mitigation of salinity stress and increasing plant growth. It assesses morphological, biochemical, physiological and molecular changes induced in plants suffering from salinity when supplemented with PGPB.

Impact of saline water irrigation plus potassium sulphate application on growth and yield potential of pepper plants

The aim of this research was to investigate the impact of different saline water irrigation levels plus potassium sulphate (K2SO4) application on growth and yield potential of pepper plants. The treatments consisted of three saline water irrigation levels (2.5, 4 and 6 dS m-1) and tab water as control. Each treatment was supplemented with different levels of K2SO4 at (zero, 2 and 4 gm K2SO4 per plant), except for the control. Plant observations were collected to evaluate plant length, fruit number per plant, fruit yield per plant, stem water potential, plant transpiration, photosynthetic rate and dry matter of shoots and roots. Results of this study indicated that K2SO4 application played a positive impact on alleviating salinity stress and improving plant growth parameters mainly under saline water irrigation levels of 2.5 and 4 dS m-1 plus 2 gm K2SO4 compared to saline water irrigation treatments which were not supplemented with K2SO4.