Microbial Derived Compounds Are a Promising Approach to Mitigating Salinity Stress in Agricultural Crops

Biofilm forming, exopolysaccharide producing and halotolerant, bacterial consortium mitigates salinity stress in Triticum aestivum

Biofilm and EPS characterization of a rhizobacterial isolate BC-II-20 was done using biophysical techniques. SEM revealed surface morphology of EPS powder to be irregular porous web-like structure. FTIR spectra showed peaks of the polymeric carbohydrate functional groups with probable role in imparting biological properties to EPS. XRD analysis showed signal at 220 (2θ) and confirms its amorphous or semi-crystalline nature. EPS derived from bacterial consortium gradually increased under 200 mM, 400 mM, 600 mM and 800 mM NaCl and SEM-EDAX analysis of EPS showed increase in Na & Cl peaks under the above salt concentrations, depicting EPS-NaCl binding. Triticum aestivum plants under 200 mM NaCl stress with different combinations of treatments showed that bacterial consortium provides tolerance. Under 200 mM salt stress the shoot length was 7.74 cm and total chlorophyll was 4.16 mg g-1Fw of the uninoculated plants whereas inoculated ones were 9.94 cm and 5.62 mg g-1Fw respectively. Under salinity stress, membrane stability index was increased from 47 % to 61 % and electrolyte leakage was decreased to 48 % from 64 %, after inoculation with bacterial consortium. Therefore, consortium comprising of these halotolerant and biofilm forming, EPS producing bioinoculants provides salt tolerance and can be exploited as a sustainable alternative for stress tolerance.

Exopolysaccharides from endophytic Glutamicibacter halophytocota KLBMP 5180 functions as bio-stimulants to improve tomato plants growth and salt stress tolerance

Microbial exopolysaccharides (EPSs) can promote plants growth and protect them against various abiotic stresses, but the role of actinobacteria-produced EPSs in plant growth promoting is still less known. Here, we aim to explore the effect of EPSs from an endophyte Glutamicibacter halophytocota KLBMP 5180 on tomato seeds germination and seedlings growth under salt stress. Our study revealed that 2.0 g/L EPSs resulted in increased seed germination rate by 23.5 % and 11.0 %, respectively, under 0 and 200 mM NaCl stress conditions. Further pot experiment demonstrated that EPSs significantly promoted seedlings growth under salt stress, with increased height, root length and fibrous roots number. Plant physiological traits revealed that EPSs increased chlorophyll content, enhanced the activity of antioxidant enzymes, soluble sugar, and K+ concentration in seedlings; malondialdehyde and Na+ contents were reduced. Additionally, auxin, abscisic acid, jasmonic acid, and salicylic acid were accumulated significantly in seedlings after EPSs treatment. Furthermore, we identified 1233 differentially expressed genes, and they were significantly enriched in phytohormone signal transmission, phenylpropanoid biosynthesis, and protein processing in endogenous reticulum pathways, etc. Our results suggest that KLBMP 5180-produced EPSs effectively ameliorated NaCl stress in tomato plants by triggering complex regulation mechanism, and showed application potentiality in agriculture.

Lactobacillus helveticus EL2006H cell-free supernatant enhances growth variables in Zea mays (maize), Glycine max L. Merill (soybean) and Solanum tuberosum (potato) exposed to NaCl stress

Plant growth promoting microorganisms and their derived compounds, such as cell-free supernatant (CFS), enhance plant growth under stressed and non stressed conditions. Such technology is sustainable and environmentally friendly, which is desirable amidst the climate change threat. The current study evaluated the effect of CFS obtained from Lactobacillus helveticus EL2006H on its ability to enhance mean percentage germination and mean radicle length of corn and soybean, as well as growth parameters of potato, using treatment formulations that consisted of 0.2 and 1.0% [v/v] L. helveticus EL2006H CFS concentrations and 100 mM NaCl and 150 mM NaCl levels. Results show that treatment with 100 mM NaCl lowered percentage germination of corn by 52.63%, at 72 h, and soybean by 50%, at 48 h. Treatment with 100 NaCl +0.2% EL2006H enhanced percentage germination of soybean by 44.37%, at 48 h, in comparison to that of the 100 mM NaCl control. One hundred mM NaCl lowered radicle length of corn and soybean by 38.58 and 36.43%, respectively. Treatment with 100 Mm NaCl +1.0% EL2006H significantly increased radicle length of corn by 23.04%. Treatment with 100 mM NaCl +0.2% EL2006H significantly increased photosynthetic rate, leaf greenness and fresh weight of potato. Increasing NaCl concentration to 150 NaCl lowered the effectiveness of the 0.2% EL2006H CFS on the same growth variables of potato. In general, the lower CFS concentration of 0.2% was more efficient at enhancing germination in soybean while the higher concentration of 1.0% was more efficient at enhancing radicle length of corn. There was an observed variation in the effectiveness of L. helveticus EL2006H CFS across the different CFS concentrations, NaCl levels and crop species studied. In conclusion, based on findings of this study, CFS obtained from L. helveticus can be used as a bio stimulant to enhance growth of corn, soybean and potato. However, further studies need to be conducted, for validation, especially under field conditions, for commercial application.

Flavonoids and Devosia sp SL43 cell-free supernatant increase early plant growth under salt stress and optimal growth conditions

Salt stress is a major threat to modern agriculture, significantly affecting plant growth and yield, and causing substantial economic losses. At this crucial time of increasing climate change conditions, soil salinity will continue to develop and become an even more serious challenge to crop agriculture. Hence, there is a pressing need for sustainable techniques in agricultural production that could meet the dual challenges of crop productivity and environmental instability. The use of biostimulants in agricultural production has greatly influenced plant health and global food production. In particular, the application of bioactive materials produced by beneficial microbes is becoming a common practice in agriculture and provides numerous benefits to plant growth and resistance to stressful conditions. In this research two biostimulants; a type of plant secondary metabolite (flavonoids) and a microbe-based material (CFS: Cell-Free Supernatant) containing active compounds secreted by a novel bacterial strain isolated from Amphecarpaea bracteata root nodules (Devosia sp - SL43), have been utilized to improve the growth and stress resistance of two major oil seed crops; canola and soybean, under optimal and salt stress conditions. Our findings suggested significant improvements in crop growth of canola and soybean following the application of both biostimulants. Under optimal growth conditions, soybean growth was significantly affected by foliar spray of flavonoids with increases in shoot fresh and dry weight, and leaf area, by 91, 99.5, and 73%, respectively. However, soybean growth was unaffected by flavonoids under salt stress. In contrast, CFS with a meaningful capacity to mitigate the negative effects of salinity stress improved soybean shoot fresh biomass, dry biomass, and leaf area by 128, 163 and 194%, respectively, under salt stress conditions. Canola was less responsive to both biostimulants, except for canola root variables which were substantially improved by flavonoid spray. Since this was the first assessment of these materials as foliar sprays, we strongly encourage further experimentation to confirm the findings reported here and to determine the full range of applicability of each of these potential technologies.

Cell-Free Supernatant Obtained From a Salt Tolerant Bacillus amyloliquefaciens Strain Enhances Germination and Radicle Length Under NaCl Stressed and Optimal Conditions

Seed germination and early plant growth are key stages in plant development that are, susceptible to salinity stress. Plant growth promoting microorganisms (PGPMs) produce substances, in their growth media, that could enhance plant growth under more optimal conditions, and or mitigate abiotic stresses, such as salinity. This study was carried out to elucidate the ability of a NaCl tolerant Bacillus amyloliquefaciens strain's cell-free supernatant to enhance germination and radicle length of corn and soybean, under optimal and NaCl stressed growth conditions. Three NaCl levels (0, 50, and 75 mM) and four cell-free supernatant concentrations (1.0, 0.2, 0.13, and 0.1% v/v) were used to formulate treatments that were used in the study. There were observed variations in the effect of treatments on mean radicle length and mean percentage germination of corn and soybean. Overall, the study showed that Bacillus amyloliquefaciens (BA) EB2003 cell-free supernatant could enhance mean percentage germination and or mean radicle length of corn and soybean. At optimal conditions (0 mM NaCl), 0.2% BA, 0.13% BA, and 0.1% BA concentrations resulted in 36.4, 39.70, and 39.91%, increase in mean radicle length of soybean, respectively. No significant observations were observed in mean radicle length of corn, and mean percentage germination of both corn and soybean. At 50 mM NaCl, 1.0% BA resulted in 48.65% increase in mean percentage germination of soybean, at 24 h. There was no observed effect of the cell-free supernatant on mean radicle length and mean percentage germination, at 72 and 48 h, in soybean. In corn however, at 50 mM NaCl, treatment with 0.2% BA and 0.13% BA enhanced mean radicle length by 23.73 and 37.5%, respectively. The resulting radicle lengths (43.675 and 49.7125 cm) were not significantly different from that of the 0 mM control. There was no observed significant effect of the cell-free supernatant on mean germination percentage of corn, at 50 mM NaCl. At 75 mM NaCl, none of the treatments enhanced mean radicle length or mean percentage germination to levels significantly higher than the 75 mM NaCl. Treatment with 1.0% BA, however, enhanced mean percentage germination to a level not significantly different from that of the 0 mM control, at 72 h. Likewise, in corn, none of the treatments enhanced radicle length to lengths significantly higher than the 75 mM control, although treatment with 1.0% BA, 0.13% BA, and 0.1% BA elongated radicles to lengths not significantly different from the 0 mM NaCl control. Treatment with 0.2% BA, 0.13% BA, and 0.1% BA resulted in mean percentage germination significantly higher than the 75 mM NaCl by 25.3% (in all 3), not significantly different from that of the 0 mM NaCl. In conclusion, concentration of cell-free supernatant and NaCl level influence the effect of Bacillus amyloliquefaciens strain EB2003A cell-free supernatant on mean percentage germination and mean radicle length of corn and soybean.