Halotolerant rhizobacteria Pseudomonas pseudoalcaligenes and Bacillus subtilis mediate systemic tolerance in hydroponically grown soybean (Glycine max L.) against salinity stress

Abstract

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 10 6 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.

Identification of New Biocontrol Agent against Charcoal Rot Disease Caused by Macrophomina phaseolina in Soybean (Glycine max L.)

“…We found that the RWC content of B. clausii treated plants was higher in stressed and non-stressed conditions which indicates that this strain was able to limit the advancement of a fungal pathogen in the plant body. Moreover, it also helped the plants to retain the water content necessary for proper functioning as indicated by previous studies regarding RWC of plants subjected to various types of stresses [24,57].…”

“…Proline is an amino acid that plays a beneficial role in plants against biotic and abiotic stresses. It is an efficient osmolyte and besides this, it also plays other significant roles in stressed plants, i.e., it acts as an antioxidant molecule, signaling molecule, and a metal chelator [24,60]. The results for the proline contents of charcoal rot stressed plants were more pronounced in the case of B. clausii treated plants as compared to that of P. putida.…”

“…Seeds were decontaminated by being continuously shaken in 70% ethanol for 1 min and then in 4% NaOCl solution for 3 min followed by subsequent washing with sterile water at each step [24]. Seed bacterization at the rate of 10 6 CFU/mL was performed following the method of Zia et al [22].…”

“…DNA of potent biocontrol agents (CW1 and CW2) was extracted by standard cetyl trimethylammonium bromide (CTAB) technique of Sambrook and Russell [25]. Amplification of the 16S rRNA gene was done by using the reported primers and conditions as described by Yasmin et al [24]. After that, amplified products were sequenced by using the commercial service of Macrogen Korea.…”

Halo-tolerant plant growth promoting rhizobacteria for improving productivity and remediation of saline soils

“…In a study it was shown that HT-PGPR Bacillus subtilis reduced the absorption of Na + by Arabidopsis thaliana roots through down-regulation of high-affinity K + transporter (HKT1) in salt-affected conditions [41] . Yasmin et al [45] revealed that inoculation of salt-stressed soybean plants with Pseudomonas pseudoalcaligenes triggered synthesis of key defense enzymes that reduced the Na + concentration in roots and shoots simultaneously balancing the cellular condition by increasing intracellular K + levels. Similarly, Pseudomonas koreensis strain AK-1 reduced Na + and elevated K + levels in Glycine max L. Merrill [46] .…”