| The approach of solving the food crisis lies in raising the yield of rice. Application of chemical fertilizers and pesticides has been considered as the main way to increase the yield of rice and control diseases. However, the chemical fertilizers and pesticides break the ecological balance and harm the environment. Biological fertilizers characterized by high efficiency, low cost, innocuity and economization of energy, may make up for the limitations and disadvantages of chemical fertilizers. The critical problem of developing and utilizating microbial fertilizers is to screen bacterial strains with high efficient nitrogen fixation, phosphate-solubilizing or pathogen resistance.A series of plant growth-promoting rhizobacteria (PGPR) strains with nitrogen fixation, phosphate-solubilizing or pathogen resistance were isolated from the rhizosphere of rice in fields of Huazhong Agricultural University. The test of gas chromatogram to mensurate enzyme activity of nitrogen fixation the value of strain NW1 and NW2 were the highest, which reached up to 1.004μmol C2H4·mL-1·h-1 and 0.906μmol C2H4·mL-1·h-1 respectively. Molybdenum-antimony ultraviolet colorimetry tests showed that the soluble phosphorus in minimum media with only phosphorite powder inoculated by PI1 was 106.8μg·mL-1, which was around 67.5 times with control (1.582μg·mL-1). Besides, the soluble phosphorus concentration of PA10 and PH2 were 3.885μg·mL-1 and 2.459μg·mL-1 respectively. In vitro antagonistic assay showed that strain PH2 and strain W8 effectively suppressed the growth of the two main rice pathogens (Rhizoctonia solani and Magnaporthe grisea).Based on phenotypic, physiological, biochemical and phylogenetic studies, the six PGPR were classified as members of Azotobacter chrococcum, Agrobacterium sp., Pantoea agglomerans, Burkholderia vietnamiensis and Chromobacterium. haemolyticum. Currently, this is the first report on these novel functions of C. haemolyticum, which suggests that strain W8 is a novel PGPR strain.The results of water culture experiments showed that the six PGPR except NW1 had growth-promoting effects. Unfortunately, the dates between water culture essay and the above or pot experiments were not consistent. The nitrogen-fixing pot experiment results demonstrated that NW1 and NW2 strains promoted rice biomass and nitrogen content of rice. The promoting effect of strain NW2 reached a significant level:compared with the non- inoculated control, fresh weight, plant height and the root length of rice increased by 32.7%,15.1% and 74.8%, and the total nitrogen also increased around 40%. Phosphate-solubilizing pot experiments showed that PI1 and PA10 strains effectively improved the rice biomass and the absorption of phosphorus of rice.Inoculating strain PI1, fresh weight, plant height and root length of rice were higher than control one, increasing by 1.64,1.20 and 1.57 times. Even though strain PH2 did not have the ability of promotion, it effectively suppressed the growth of the two main rice pathogens. The results of pot experiments indicated that the strain W8 induced the plant growth significantly by increasing fresh weight, plant height, root length and nutrient element (N and P) contents of rice. In addition, the results of pot experiment indicated that soaking seeds and foliar spraying of strain W8 on rice significantly decreased blast and sheath blight development by 47% and 52%, respectively, as compared to the control.This study obtained six efficient PGPR with nitrogen fixation, phosphate-solubilizing or pathogen resistance. Especially, with outstanding performances, NW2, PI1 and W8 can be used as potential inoculants of rice. It will be significant for further studies on the rhizosphere of rice and applications of PGPR as biofertilizers and biopesticides. |
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