Screening And Identification Of Rhizosphere Growth-promoting Bacteria And Their Growth-promoting Effect On Continuous Cropping Soybean

In order to obtain plant growth-promoting rhizobacteria(PGPR)with resistance to continuous cropping obstacles,soybean rhizosphere soil was collected from lindian County test base in Daqing City,Heilongjiang Province.After isolation and purification,the growth-promoting strains were screened out through seed germination and seedling stage test.Morphological,physiological and biochemical indexes,16S r DNA molecular biological identification of the preliminary screened strains were carried out,and the capacity of nitrogen fixation,phosphorus solubility,IAA secretion and ACC deaminase activity of the strains were measured.Furthermore,PGPR strains with excellent growth promoting characteristics were screened out and constituted as growth promoting agent.The growth promoting effect of PGPR strains on continuous cropping soybean was studied through pot experiment and field experiment.The main results and conclusions are as follows:Firstly,rhizosphere bacteria were isolated from continuous cropping soybean rhizosphere soil and inoculated in functional medium(phosphorus soluble and nitrogen fixing)for screening,112 strains of nitrogen-fixing bacteria and 52 strains of phosphorus soluble bacteria were obtained.The functional growth-promoting strains were screened by seed germination and seedling growth promoting test,and 22 strains with growth-promoting effect were obtained,among which C27,XC22,C22-1 and XC75 had good growth-promoting effect on germination and seedling growth of soybean.Secondly,the PGPR strains screened by the test were identified as Pseudomonas,Enterobacter,Agrobacterium,Citrobacter,Serratia,and Klebsiella.After comparison,10 different strains were determined.Thirdly,the growth promoting characteristics of 10 PGPR strains were studied.Nine of the 10PGPR strains had phosphorus solubilizing capacity,and the effective phosphorus increasing capacity ranged from 0.19 mg·L^-1to 17.49 mg·L^-1.XC22 strain had the strongest Effective phosphorus solubility.Ten strains had the ability to fix nitrogen,among which C22-1 and XC98strains had the strongest ability to fix nitrogen.All the 10 strains could secrete IAA,and the yield ranged from 17.72?g·m L^-1to 88.21?g·m L^-1.C27 and XC98 had the strongest ability to produce IAA,with 75.65?g·m L^-1and 88.21?g·m L^-1,respectively.All the 10 strains had ACC deaminase activity,which ranged from 0.33 U·mg^-1to 0.67 U·mg^-1.XC75 had the highest ACC deaminase activity.Fourthly,five excellent growth-promoting strains without antagonism were selected to form the agent for soybean resistance(tolerance)to continuous cropping.The results showed that the agent had good growth-promoting effect on the morphology,chlorophyll content and SOD activity of soybean seedlings.Meanwhile,the agent could enhance the nodule formation ability of soybean during harvest period,and had a good yield increase effect.