Encapsulation Of Relieve Salt Stress And Growth-promoting SRPG-396 Strain And Its Interaction Property With Cotton

In view of the serious salinization of Xinjiang and the microbial inoculums, either seed coating or seed soaking application on cotton will be directly exposed to the soil environment, causing short survival time, poor stability. In this study, the phosphorus solubilization properity of SRPG-396 strains and the growth-promoting properity for cotton seedlings on phosphorus absorption and distribution were studied. Secondly, the NaAlg-B-S SRPG-396 microcapsules formulation were developed, which can improve cell survival and persistence effectively. Lastly, the colonization, survival period of encapsulated SRPG-396 strains in cotton rhizosphere, and the mechanisms of alleviating salt stress and growth-promoting on cotton was described through pot experiment under simulating different soil salinization condition. The main results are as follows:The study was performed to investigate the efficiency of rhizobacteria SRPG-396 on solubilization of insoluble phosphate and growth-promoting effect on cotton under the salinization. The results showed that the effective phosphorus content was negatively correlated with the pH of the fermentation liquid and could reach to 56.75 mg/L with the addition of soluble Ca3(PO4)2. Pot experiment showed that the SRPG-396 agents can significantly improve the cotton seedling fresh weight, dry weight and root dry weight by 17.84%, 33.66% and 13.79% under salt stress, respectively. In addition, the SRPG-396 agents can improve the total P content by 20%, 11.51% in cotton stems and leaves, root under the condition of salt stress, respectively.The SRPG-396 strain can be successfully encapsulated in spherical SRPG-396 NaAlg-B-S microcapsules prepared by extrusion. The FTIR and XRD findings in this study showed that absence of chemical reactions and good mixing performance were detected with alginate, starch, and bentonite. The survival rates of SRPG-396 were 81.07% and 89.67% in free and encapsulated bacteria, respectively, after storage 50 day at 4°C. Also, the production of indole-3-acetic acid and gibberellins were not degraded after microencapsulation, maintained at 40 ng/mL and 0.18 ng/mL during storage, sufficient to meeting the needed for plant growth. The NaAlg-B-S microcapsule can significantly improve the storage stability of SRPG-396 strains.The mechanism of alleviating salt stress and growth-promoting on cotton were described through pot experiment under simulating different soil salinization condition. After sowing for 21 days, inoculation of encapsulated SRPG-396 strains can improve the biomass of cotton seedlings. Inoculated encapsulated SRPG-396 treatment significantly increased the plant height by 20.62%, germination rate 56.69%, fresh weight 36.56% and dry weight 20.30% under 0.5% salt stress, respectively. Inoculated encapsulated SRPG-396 treatment significantly increased the soluble sugar, soluble protein, chlorophyll a, b and carotenoids contents by 275.87%, 19.47%, 40.53%, 26.16% and 7.87% under 0.5% salt stress, respectively. Besides, an approximately 42.30%, 12.54% and 5.75% decreased in the proline, MDA content and POD activity with encapsulated SRPG-396 inoculated under 0.5% salt stress, respectively.The colonization, survival rates of the encapsulated SRPG-396 and free bacteria in cotton rhizosphere were determined under simulating soil salinization condition. The colonization number on the rhizosphere vermiculite and root by encapsulated SRPG-396 treatment was less than that free SRPG-396 treatment from 7 to 21 days, significantly higher than that after 35 days, and sustained for up to 63 days. Although, the population size of viable bacteria on rhizosphere vermiculite in plant treatment was less than that non-plant treatment, the total number of viable bacteria on rhizosphere in plant treatment was higher than that non-plant treatment. Inoculation of encapsulated SRPG-396 strains can improve the potassium(8.25%, 10.80%), calcium(19.69%, 13.30%), magnesium(23.96%, 4.56%) accumulation in the stem leaf and root under the condition of 2% salt stress, while reduced the sodium absorption. The ratio of Na+/Ca2+ and Na+/K+ will increase by the salt, but the toxic effects can be alleviated by application of encapsulated SRPG-396 strains.In conclusion, encapsulated SRPG-396 strain could effectively colonizated on the cotton root and relieved salt stress under saline conditions. The microcapsules bioinoculants are potential alternatives for sustainable agriculture due to their low cost of production.