Isolation,Screening And Application Of Plant Growth Promoting Rhizobacteria

Soil compaction and decrease of soil fertility frequently occur due to long-term use of chemical fertilizers.Plant growth promoting rhizobacteria(PGPR)are capable of promoting the growth of plants and enhancing yield of crops,and play important roles for sustainable and environmentally friendly crop production.Explotation and application of PGPR can reduce the deterioration and contamination of soil resulted from excessive usage of chemical fertilizers,as well as the cost of agriculture production.In the present study,PGPR strains were isolated from the rhizosphere soil of selected crops(peanut,pepper,corn and tomato)in Nanyang city,and their abilities to dissolve phosphorus were tested.The PGPR strains capable of dissoving phosphorus were further tested on their potentials to fix nitrogen,and to dissolve potassium,as well as their productivity of indole acetic acid(IAA).The physiological and biochemical characteristics of the strains were further analysed.The strains were identified on the based of their 16S rDNA sequences.In addition,seed germination tests,potted planting and field experiments were carried out to determine growth-promoting and yield-enhancing effects of the strains on wheat and corn.The main research results are summarized as follows.1.A total of 21 bacterial strains were preliminarily screened by using inorganic phosphorus solid plate method.Quantitative screening of phosphorous soluble strains were conducted by molybd-antimony anti-colorimetric method.Salkowski colorimetric method was used for quantitative determination of IAA produced by the strains.As a result,three strains with strong ability to dissolve phosphorus were obtained:HS1-1(available phosphorous 31.03 mg/L),HS2-2(available phosphorous 30.26 mg/L)and HS2-1(available phosphorous 27.85 mg/L).Two strains(LX-2 and LX-4)with a high level of IAA productivity were obtained.The concentrations of the produced IAA were 89.55 mg/L for LX-2 and 107.32 mg/L for LX-4,respectively.2.Based on the analyses of physiological and biochemical characteristics and 16S rDNA homology sequences,the 6 bacterial strains were separately identified as Enterobacteriaceae bacterium(LX-2,LX-4),Bacillus thuringiensis(No.8)and Burkholderia spp.(HS1-1,HS2-1,HS2-2).3.The effect of the experimental PGPR strains on seed germination and seedling growth of corn,red bean,peanut and rapeseed were tested.The germination rates of corn,red bean and peanut seeds in the HS2-1 treatment group were higher than that of their respective control groups in different degrees,showing growth promotion effect on the crop seeds.The seedling height of the strain LX-2 treatment group was significantly higher than the control group on both corn and peanut.The strain HS1-1 treatment group showed significant growth promoting effects on both rape and red bean.In order to further confirm the growth promotion effect of the six experimental strains on grain crops,pot experiments were conducted on 3 maize varieties(Zhongyu 9,Chuangyu 198 and Bonong 418).Strain LX-4 showed significant growth promoting effects on Zhongyu 9 and Chuangyu 198 based on the parameter of plant height,with an enhanced rate of 12.2%and 12.3%,respectively,compared to their respective controls.As revealed by plant fresh and dry weights,strain HS1-1 showed significant growth promoting effects on the three maize varieties tested.4.In terms of yield per 666.7 m~2,strain HS1-1 significantly increased the yield on three wheat varieties(Zhengmai 113,Deyan 8 and Zhoumai 18),as well as on the two maize varieties(Bonong 418 and Chuangyu 198).Strains HS2-2 and LX-4 were found to have significantly high efficacies in promoting plant growth and enhancing yield compared to other strains.5.In order to determine the growth promotion effects of PGPR strains on wheat and maize plants in field conditions,seeds of wheat and maize were treated by the experimental strains and sown,and the growth and productive parameters(wheat tiller number,wheat thousand kernel weight,corn hundred kernel weight,yield per 666.7 m~2)were investigated.To know the variations of stree-resistance-related enzymes and leaf temperature on the varieties treated by the experimental strains,the activities of superoxide dismutase(SOD),polyphenol oxidase(POD),catalase(CAT)and flag leaf midday temperatures were separately measured.The field occurrence of maize brown spot disease was investigated.All of the four strains(HS2-2,No.8,LX-2 and HS1-1)enhanced the enzyme activities to different degrees on the two tested crops.The flag leaf midday temperatures of strains LX-4 and HS1-1 treatment groups were lower than that of their respective controls.The control efficacy of strain HS2-1 against maize brown spot disease was 12.19%-51.44%,compared with the control,followed by strain HS1-1,revealing that a few experimental strains might have the potential to enhance resistance of grain crops against diseases.