Research On Enhanced Alfalfa Tolerance To Saline-alkali Stress By Pgpr Co-inoculation

The growth and development of plants were seriously influenced by saline-alkali stress. The interaction of plant growth promoting rhizobacteria(PGPR) containing ACC deaminase with plant is a viable strategy, because PGPR could alleviate the saline-alkali stress, and stimulate plant growth. However, many biological functions can’t be completed by one kind of microbe, they must rely on a variety of microorganisms with different biological functions to work together. In this study, co-inoculated PGPR combinations were selected by antagonistic reaction, the characteristics of growth-promoting of selected strain combinations were evaluated, and investigate the effect of growth of alfalfa using selected strain combinations under saline-alkali stress. The study laid the foundation of the development of bio-fertilizer. The main results were as follows: 1. Screening of co-inoculated strain combinationsEight co-inoculated strain combinations were selected by antagonistic reaction. Then 6 co-inoculated strain combinations were selected based on alfalfa seed germination tests under saline-alkali stress and the conditions of strain culture. The 6 co-inoculated strain combinations were LJL-11+LJL-5, LJL-11+C-7, LJL-11+MJM-11, C-7+MJM-11, LJL-5+MJM-11, and LJL-12+LJL-5. 2. Characteristics of growth-promoting of the co-inoculated strain combinationsCompared with single strain, the ability of the co-inoculated strain combinations were enhanced on ACC deaminase, IAA, inorganic phosphorus solubilization and nitrogen fixation. The ACC deaminase of co-inoculated strain combinations LJL-11+MJM-11, LJL-11+C-7 and C-7+MJM-11 were significantly increased compared with single strain(P < 0.05). When the L-Trp concentration was 500 μg/m L, the IAA contents of LJL-5+MJM-11, LJL-11+MJM-11, LJL-12+LJL-5 and LJL-11+LJL-5 were significantly increased than the single strain(P < 0.05). Except C-7+MJM-11, the phosphorus solubilizatin abilities of remaining strain combinations were significant higher than the single strain(P < 0.05). The co-inoculated strain combinations LJL-11+LJL-5, LJL-11+C-7, LJL-11+MJM-11, C-7+MJM-11 and LJL-5+MJM-11 showed higher nitrogen fixation compared with single strain(P < 0.05). 3. Effect of growth-promoting by by co-inoculated strain combinationsCompared with no PGPR control, single strain and co-inoculated strain combinations could promote alfalfa growth in different extent. The significantly increased effect of plant growth promotion were found in co-inoculated strain combinations LJL-11+LJL-5, LJL-11+C-7, LJL-11-MJM-11, C-7+MJM-11, LJL-5+MJM-11 and LJL-12+LJL-5(P < 0.05). The dry weight of shoot were increased by 36.42%, 36.42%, 58.94%, 43.05%, 52.98% and 43.05%, respectively, and the dry weight of root were increased by 52.08%, 56.25%, 45.83%, 64.58%, 45.83% and 68.75%, respectively. In terms of the quality of nutrition, compared with the inoculation alone, co-inoculated strain combination C-7+MJM-11 increased crude protein and phosphorus content of alfalfa, the protein content is 19.54%, and the content of phosphorus increased the most. 4. The evaluation of alfalfa resistance related indicatorsCompared with inoculation alone, the leaf chlorophyll contents of alfalfa inoculated with co-inoculated strain combinations alfalfa were significantly increased(P < 0.05). The soluble protein of alfalfa inoculated with LJL-11+LJL-5, LJL-11+C-7, LJL-11-MJM-11, C-7+MJM-11, LJL-5+MJM-11 and LJL-12+LJL-5 were significantly increased than inoculation alone group(P < 0.05). The malondialdehyde content of alfalfa inoculated with strain combination were significantly reduced compared with single inoculation and no-inoculated control(P < 0.05).