Amelioration of Salt Stress on Annual Ryegrass by ACC Deaminase-Containing Plant Growth-Promoting Rhizobacteria

Four strains of plant growth-promoting rhizobacteria (PGPR) were isolated from the rhizosphere of salty plants, based on the ability to utilize the compound 1-aminocyclopropane-1-carboxylic acid (ACC) as a sole nitrogen source. These four bacterial isolates, especially Pseudomonas sp. S1, alleviated greatly salt stress and promoted significantly the seedling growth of annual ryegrass under either 5 or 10 g/kg NaCl stress in gnotobiotic growth pouch assay. Compared with control (no NaCl), more plant promotion was observed under 10 g/kg NaCl stress. The greatly significant positive correlations between ACC deaminase activity of four bacterial isolates and plant growth parameters (root length and shoot length) were observed. Results of soil pot trial also revealed that inoculation with Pseudomonas sp. S1 significantly increased the root dry weight and shoot dry weight of annual ryegrass under 5 g/kg NaCl stress over 50 days. The results may imply that inoculation with ACC deaminase-containing PGPR may serve as an environmentally-friendly and economical alternative to the amelioration of increasingly saline soils.