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Enhancement of alfalfa yield and quality by plant growth-promoting rhizobacteria under saline-alkali conditions.

BACKGROUND
Bacteria with 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity could decrease the ethylene level, confer resistance of plant, and stimulate plant growth under biotic and abiotic stress conditions.


RESULTS
Plant growth-promoting rhizobacteria (PGPR) strains Enterobacter aerogenes (LJL-5) and Pseudomonas aeruginosa (LJL-13) were obtained from the rhizosphere of alfalfa grown under saline-alkali conditions. The ACC deaminase activity of E. aerogenes (LJL-5) and Ps. aeruginosa (LJL-13) was approximately 2-5 µmol mg-1  h-1 . indole acetic acid synthesis was increased with the increasing concentration of l-tryptophan. Siderophore production and phosphate solubilization in Ps. aeruginosa (LJL-13) were higher than those in E. aerogenes (LJL-5). Compared to the non-inoculated seedlings (1.31 ng mL-1  h-1 ), inoculated alfalfa seedlings with E. aerogenes (LJL-5) (0.90 ng mL-1  h-1 ) and Ps. aeruginosa (LJL-13) (0.78 ng mL-1  h-1 ) emitted lower levels of ethylene. Under saline-alkali conditions in the greenhouse, inoculation with E. aerogenes (LJL-5) and Ps. aeruginosa (LJL-13) increased the biomass, soil and plant analyzer development (SPAD), and P content of alfalfa plants, and also induced the activity of antioxidant enzymes (superoxide dismutase, peroxidase and catalase), promoted the accumulation of antioxidant substances and removed various harmful substances. Under saline-alkali conditions in the field (2012, 2013, and 2014), inoculation of alfalfa with E. aerogenes (LJL-5) and Ps. aeruginosa (LJL-13) significantly increased the shoot height, fresh and dry weights, yield and crude protein content of alfalfa plants, but decreased the fiber content.


CONCLUSION
Two PGPR strains were isolated from the rhizosphere of alfalfa in saline-alkali conditions. Both strains could promote alfalfa growth in saline-alkali soil, and could be used as biofertilizer to promote plant growth under stress and reduce environmental pollution caused by fertilizers simultaneously. © 2018 Society of Chemical Industry.