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Salt stress is one of the devastating factors that hampers growth and productivity of soybean. Use of Pseudomonas pseudoalcaligenes to improve salt tolerance in soybean has not been thoroughly explored yet. Therefore, we observed the response of hydroponically grown soybean plants, inoculated with halotolerant P. pseudoalcaligenes (SRM-16) and Bacillus subtilis (SRM-3) under salt stress. In vitro testing of 44 bacterial isolates revealed that four isolates showed high salt tolerance. Among them, B. subtilis and P. pseudoalcaligenes showed ACC deaminase activity, siderophore and indole acetic acid (IAA) production and were selected for the current study. We determined that 106 cells/mL of B. subtilis and P. pseudoalcaligenes was sufficient to induce tolerance in soybean against salinity stress (100 mM NaCl) in hydroponics by enhancing plant biomass, relative water content and osmolytes. Upon exposure of salinity stress, P. pseudoalcaligenes inoculated soybean plants showed tolerance by the increased activities of defense related system such as ion transport, antioxidant enzymes, proline and MDA content in shoots and roots. The Na+ concentration in the soybean plants was increased in the salt stress; while, bacterial priming significantly reduced the Na+ concentration in the salt stressed soybean plants. However, the antagonistic results were observed for K+ concentration. Additionally, soybean primed with P. pseudoalcaligenes and exposed to 100 mM NaCl showed a new protein band of 28 kDa suggesting that P. pseudoalcaligenes effectively reduced salt stress. Our results showed that salinity tolerance was more pronounced in P. pseudoalcaligenes as compared to B. subtilis. However, a detailed study at molecular level to interpret the mechanism by which P. pseudoalcaligenes alleviates salt stress in soybean plants need to be explored.

Susceptibility of plants to abiotic stresses, including extreme temperatures, salinity and drought, poses an increasing threat to crop productivity worldwide. Here the drought-induced response of maize was modulated by applications of methyl jasmonate (MeJA) and salicylic acid (SA) to seeds prior to sowing and to leaves prior to stress treatment. Pot experiments were conducted to ascertain the effects of exogenous applications of these hormones on maize growth, physiology and biochemistry under drought stress and well-watered (control) conditions. Maize plants were subjected to single as well as combined pre-treatments of MeJA and SA. Drought stress severely affected maize morphology and reduced relative water content, above and below-ground biomass, rates of photosynthesis, and protein content. The prolonged water deficit also led to increased relative membrane permeability and oxidative stress induced by the production of malondialdehyde (from lipid peroxidation), lipoxygenase activity (LOX) and the production of H2O2. The single applications of MeJA and SA were not found to be effective in maize for drought tolerance while the combined pre-treatments with exogenous MeJA+SA mitigated the adverse effects of drought-induced oxidative stress, as reflected in lower levels of lipid peroxidation, LOX activity and H2O2. The same pre-treatment also maintained adequate water status of the plants under drought stress by increasing osmolytes including proline, total carbohydrate content and total soluble sugars. Furthermore, exogenous applications of MeJA+SA approximately doubled the activities of the antioxidant enzymes catalase, peroxidase and superoxide dismutase. Pre-treatment with MeJA alone gave the highest increase in drought-induced production of endogenous abscisic acid (ABA). Pre-treatment with MeJA+SA partially prevented drought-induced oxidative stress by modulating levels of osmolytes and endogenous ABA, as well as the activities of antioxidant enzymes. Taken together, the results show that seed and foliar pre-treatments with exogenous MeJA and/or SA can have positive effects on the responses of maize seedlings to drought.

Key messageA detailed study of the response of wheat plants, inoculated with drought-tolerant PGPR is studied which would be beneficial to achieve genetic improvement of wheat for drought tolerance.Drought stress, a major challenge under current climatic conditions, adversely affects wheat productivity. In the current study, we observed the response of wheat plants, inoculated with drought-tolerant plant growth-promoting rhizobacteria (PGPR) Bacillus megaterium (MU2) and Bacillus licheniformis (MU8) under induced drought stress. In vitro study of 90 rhizobacteria exhibited 38 isolates showed one or more plant growth-promoting properties, such as solubilization of phosphorus, potassium, and exopolysaccharide production. Four strains revealing the best activities were tested for their drought-tolerance ability by growing them on varying water potentials (− 0.05 to − 0.73 MPa). Among them, two bacterial strains Bacillus megaterium and Bacillus licheniformis showed the best drought-tolerance potential, ACC deaminase activities, IAA production, and antagonistic activities against plant pathogens. Additionally, these strains when exposed to drought stress (− 0.73 MPa) revealed the induction of three new polypeptides (18 kDa, 35 kDa, 30 kDa) in Bacillus megaterium. We determined that 106 cells/mL of Bacillus megaterium and Bacillus licheniformis were enough to induce drought tolerance in wheat under drought stress. These drought-tolerant strains increased the germination index (11–46%), promptness index (16–50%), seedling vigor index (11–151%), fresh weight (35–192%), and dry weight (58–226%) of wheat under irrigated and drought stress. Moreover, these strains efficiently colonized the wheat roots and increased plant biomass, relative water content, photosynthetic pigments, and osmolytes. Upon exposure to drought stress, Bacillus megaterium inoculated wheat plants exhibited improved tolerance by enhancing 59% relative water content, 260, 174 and 70% chlorophyll a, b and carotenoid, 136% protein content, 117% proline content and 57% decline in MDA content. Further, activities of defense-related antioxidant enzymes were also upregulated. Our results revealed that drought tolerance was more evident in Bacillus megaterium as compared to Bacillus licheniformis. These strains could be effective bioenhancer and biofertilizer for wheat cultivation in arid and semi-arid regions. However, a detailed study at the molecular level to deduce the mechanism by which these strains alleviate drought stress in wheat plants needs to be explored.

Fusarium verticillioides is an important fungal pathogen of maize, causing stalk rot and severely affecting crop production. The aim of this study was to characterize the protective effects of formulations based on Jacaranda mimosifolia leaf extracts against F. verticillioides in maize . We compared different seed treatments comprising J. mimosifolia extracts, chemical fungicide (mefenoxam) and salicylic acid to modulate the defense system of maize host plants. Both aqueous and methanolic leaf extracts of J. mimosifolia (1.2% w/v) resulted in 96–97% inhibition of mycelial growth of F. verticillioides . While a full-dose (1.2%) extract of J. mimosifolia provided significant protective effects on maize plants compared to the inoculated control, a half-dose (0.6% w/v) application of J. mimosifolia in combination with half-strength mefenoxam was the most effective treatment in reducing stalk rot disease in pot and field experiments. The same seed treatment significantly upregulated the expression of genes in the leaves encoding chitinase, glucanase, lipid transfer protein, and pathogenesis-related proteins PR-1, PR-5 and PR-10, 72 h after inoculation. This treatment also induced the activities of peroxidase, polyphenol oxidase, protease, acid invertase, chitinase and phenylalanine ammonia lyase. We conclude that seed pre-treatment with J. mimosifolia extract with half-strength chemical mefenoxam is a promising approach for the management of stalk rot in maize.

Drought stress imposes a serious challenge to cultivate wheat, restricting its growth. Drought reduces the capability of plant to uptake essential nutrients. This causes stunted growth, development and yield. Traditional ways to increase wheat growth under drought stress have shortcomings. Using plant-growth-promoting rhizobacteria (PGPR) has proved feasible and eco-friendly way to enhance wheat growth even under the drought stress. Combining PGPR in consortiums further boosts up their effects. In this study, we have checked the efficacy of drought-tolerant Bacillus halotolerans , Pseudomonas sihuiensis and Bacillus atrophaeus in combination. These strains were allowed to grow on PEG 6000 with concentrations (-0.15, -0.49, -0.73 and − 1.2) Mega Pascal (MPa) alone and in combination. Furthermore, Fourier transmission infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used. Their biochemical traits such as solubilization of K, P and Zn and the synthesis of siderophore, indole acetic acid (IAA), protease, amylase, hydrogen cyanide (HCN) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase were done. In addition to this, we investigated the optimum folic acid concentration i.e 150 ppm for wheat against drought stress. We conducted a pot experiment to check the growth-enhancing and drought-mitigating effects of consortium and folic acid alone and in combination. As a result, we found a significantly increased wheat biomass, relative water content (RWC), chlorophyll content, antioxidants including glutathione reductase and total soluble sugars and protein content under all treatments. However, the combined treatment of bacterial consortium and folic acid showed maximum potential to boost wheat growth and survival even under drought. We also investigated the minerals uptake by wheat after the treatments and found maximum nutrient uptake under the co-effect of folic acid and bacterial consortium We believe this is the first study that has investigated the optimal dose of folic acid for wheat. Our research is also novel in that we seek to investigate the effects of folic acid along with a bacterial consortium comprising Bacillus halotolerans , Pseudomonas sihuiensis and Bacillus atrophaeus on wheat grown under the drought stress. Highlights Bacillus halotolerans , Pseudomonas sihuiensis and Bacillus atrophaeus are drought tolerant strains. Their consortium significantly improves wheat growth under drought stress. 150 ppm of folic acid is the optimum concentration for wheat growth. Synergistic application of bacterial consortium and folic acid has shown promising wheat growth abilities.

Jacaranda mimosifolia trees are grown in frost-free regions globally. The aim of this study was to evaluate the methanol crude extract and various fractions of increasing polarity of J. mimosifolia leaves for bioactive metabolites, as well as antimicrobial, antioxidant and anticancer activities. The anti-inflammatory potential of the various fractions of J. mimosifolia leaf extract was studied via the lipoxygenase (LOX) inhibitory assay. Methanol crude extract (ME), derived fractions extracted with chloroform (CF) and ethyl acetate (EAF), and residual aqueous extract (AE) of dried J. mimosifolia leaves were assayed for polyphenolic compounds, their antioxidant, antimicrobial and lipoxygenase (LOX) inhibitory activities, and anticancer properties. Polyphenolic compounds were determined via HPLC while phytochemicals (total phenolics, flavonoids, tannins and ortho-diphenol contents), antioxidant activities (DPPH, hydrogen peroxideperoxide, hydroxyl and superoxide radical anions) and LOX were measured via spectrophotometry. Methanol extracts and various fractions were evaluated for antibacterial activities against Bacillus subtilis, Klebsiella pneumonia, Pseudomonas aeruginosa and Staphylococcus aureus. Antifungal potential of the fractions was tested against three species: Aspergillus flavus, Aspergillus fumigatus and Fusarium oxysporum. The highest values for total phenolic content (TPC), total flavonoid content (TFC), flavonols, tannins and ortho-diphenols were in the ME, followed by CF > EAF > AE. ME also had the highest antioxidant activity with EC50 values 48±1.3, 45±2.4, 42±1.3 and 46±1.3 μg/mL based on the DPPH, hydrogen peroxide, hydroxyl radical and superoxide radical assays, respectively. TPC and TFC showed a significant, strong and positive correlation with the values for each of these antioxidant activities. ME exhibited anti-inflammatory potential based on its LOX inhibitory activity (IC50 = 1.3 μg/mL). ME also had the maximum antibacterial and antifungal potential, followed by EAF > CF > AE. Furthermore, ME showed the strongest cytotoxic effect (EC50 = 10.7 and 17.3 μg/mL) against human hormone-dependent prostate carcinoma (LnCaP) and human lung carcinoma (LU-1) cell lines, respectively. Bioactive compounds present in leaf methanol extracts of J. mimosifolia were identified using gas chromatography-mass spectrometry (GC-MS). Fifteen compounds were identified including phenolic and alcoholic compounds, as well as fatty acids. Our results suggest that J. mimosifolia leaves are a good source of natural products with antioxidant, anti-inflammatory and anti-cancer properties for potential therapeutic, nutraceutical and functional food applications.

Two experiments (pot and field experiments) were conducted in two consecutive years to evaluate the protective effects of botanical-chemical formulations on physiological, biochemical performance and grain yield of wheat inoculated with Bipolaris sorokiniana. We compared different formulations comprising Calotropis procera, Jacaranda mimosifolia, Thevetia peruviana extracts, chemical fungicide (mefenoxam) and salicylic acid to modulate the defense system of wheat host plants. Among the selected plant species J. mimosifolia aqueous and methanolic leaf extracts (1.2% w/v) resulted in 96 to 97% inhibition against B. sorokiniana. Both in pot and field experiments, among all the formulations of selected plant extracts the combined formulation of JAF2 (J. mimosifolia 0.6%)+MFF2 (mefenoxam 0.1%) lowered the dose of chemical fungicide required to reduce the leaf spot blotch disease. The same formulation induced resistance in wheat apparently through the accumulation of peroxidase, polyphenol oxidase, protease, acid invertase, chitinase and phenylalanine ammonia lyase. This formulation also stimulated the defense-related gene expression of PR-proteins. The same treatment gave even more increase (48%, 12% and 22%) in no. of grains/spike, grains weight and grain yield, than the MFF1 (mefenoxam 0.2%). We conclude that foliar application of J. mimosifolia leaf extract with very low dose of chemical fungicide (J. mimosifolia 0.6%+mefenoxam 0.1%) is a promising approach for the management of leaf blight and spot blotch in wheat.

The efficiency of Cd-tolerant plant growth-promoting bacteria (PGPB), zinc oxide nanoparticles (ZnO NPs), and titanium dioxide nanoparticles (TiO2) in maize growing in Cd-rich conditions was tested in the current study. The best Cd-tolerant strain, Bacillus pumilus, exhibited plant growth stimulation in vivo and in vitro experiments. We determined the toxic concentrations (30 (ppm)) of both NPs for plant growth. B. pumilus, ZnO NPs (20 (ppm)), and TiO2 NPs (10 (ppm)) had a synergistic effect on plant growth promotion in Cd-contaminated soil (120 (ppm)) in a pot experiment. Both alone and in combination, these therapies reduced Cd toxicity, resulting in improved stress metabolism and defense responses. The combined treatments showed increased relative water content, photosynthetic pigments, proline, total sugars, and proteins and significantly reduced lipid peroxidation. Moreover, this combination increased the levels of minerals and antioxidants and reduced Cd bioaccumulation in shoots and roots by 40–60%. Our in silico pipeline presented a novel picture of the participation of ZnO–TiO2 protein interaction in both B. pumilus and maize. These findings provide fresh insights on the use of B. pumilus, ZnO, and TiO2 NPs, both separately and in combination, as a viable and environmentally benign strategy for reducing Cd stress in maize.

Drought stress hampers the growth and productivity of wheat crop worldwide. Thus far, different strategies have been proposed to improve drought tolerance in wheat but the combined application of plant growth-promoting rhizobacteria formulated bio-fertilizer (BF) and salicylic acid (SA) has not been thoroughly explored yet. Therefore, a pot experiment was conducted to observe the effect of SA, BF, and their combination on wheat plants under optimal and drought stress conditions. Seeds priming was done with BF (10 7 CFU mL −1 ). After 2 weeks of germination, SA (one mM) was applied as a foliar spray. Drought stress was applied by withholding water supply at three-leaf stage (30 d old plants) for the next 15 d until soil moisture dropped to 10%. Foliar application of SA increased the bacterial population of BF significantly compared to the sole application of BF under irrigated as well as drought stress conditions. Co-application of BF and foliar spray of SA induced drought tolerance in wheat plants by enhancing plant biomass, photosynthetic pigments, relative water content and osmolytes, and activities of the defense-related system. Plants treated with SA and BF together under drought stress had significantly increased leaf water status, Chl a, Chl b, and carotenoids synthesis by 238%, 125%, 167%, and 122%, respectively. Moreover, the co-application of SA and BF showed maximum SOD, POD, APX, and CAT activities by 165%, 85%, 156%, and 169% in the leaves while 153%, 86%, 116% and 200% in roots under drought stress. Similarly, the combined treatment exhibited a pronounced decrease in MDA content by 54% while increased production of proteins and proline by 145% and 149%, respectively. Our results showed that the co-application of SA and BF induced better drought tolerance as compared with the sole application of SA or BF. The results obtained herein suggest that combined application of BF and SA can be applied to the wheat crop to greatly improve drought tolerance in field conditions.

Drought is an important abiotic stress that limits the plant growth and productivity. Present investigation was aimed that plant growth-promoting rhizobacteria (PGPR) isolated from moisture-stressed area impart drought tolerance in plants and tryptophan may improve their efficiency. Pseudomonas sp. (1), Bacillus cereus and Bacillus pumilus (B. pumilus) were isolated from maize rhizosphere grown in irrigated fields, semi-arid region and arid region, respectively. Proteus sp. and Pseudomonas sp. (2) were isolated from rice rhizosphere grown in irrigated fields and raised bed. B. pumilus produced 5× more abscisic acid (ABA) in culture media than Pseudomonas sp. (1) by the addition of l-tryptophan. These inoculants also modulated the phytohormone content of maize leaves in a pot experiment. Higher ABA was produced by the application of B. pumilus and Pseudomonas sp. (2), while indole 3-acetic acid and gibberellic acid were found higher in Pseudomonas sp. (1) and Proteus sp. treated plants. Addition of l-tryptophan increased the concentration of all phytohormones in soil and leaves of maize. Maximum increase in relative water content, osmotic potential, protein content and photosynthetic pigments was recorded in B. pumilus treated maize plants. Under irrigated condition, response of Pseudomonas sp. co-inoculated with B. pumilus from arid field superseded while under drought stress the effect of later predominated. Bacillus pumilus can be used in the formulation of biofertilizer to alleviate drought stress in arid and semi-arid regions.