Screen For Plant Growth Promoting Bacteria And Investigations On Endophytic Nitrogen-fixers In Vegetables

Nitrogen-fixing microorganism reduction the nitrogen to ammonia, which play an positive role inthe process of nitrogen cycle in nature. It had a guiding significance to the efficient and sustainabledevelopment of agriculture, that screening the strain resources with nitrogen fixation and promoting.Based on the experiments in artificial climate box, greenhouse and field， our research screendiazotrophs which had growth-promoting effect on tomato and pakchoi and study the colonization andecological effect with the PCR-DGGE technology. The material were9plant root samples select from5kinds of vegetables, including tomato, cucumber, green peppers, beans and pakchoi, in order to detectand isolate the endophytic diazotrophs and analysis the biological characteristics and nifH genediversity of strains. Our research screen strains with nitrogen fixation, promoting, phosphatesolubilization and disease resistance characteristics. These strains provide excellent resources for theefficient production of agriculture and made a practical value. Specifically content as follows:Research of screening promoting bacteria and colonization in artificial climate box andgreenhouse: Based on the experiments of tomato inoculation in artificial climate box，our researchscreen the18strains with growth potential. After inoculation to plant rhizosphere,13strains can makeplant growth better than the control treatment and the effect of161-2-13treatment is the most obvious.Screening5strains and conducting the experiments of tomato inoculation in greenhouse. It found thatthe effect of4strains is obvious and the plant height, stem diameter and stem fresh weight increase at0.05significant level compared with control treatment. Preliminary inspection the4strains couldcolonize in rhizosphere soil and change the community structure at some extent, the SD1-1-1and7016treatment change greatly.Research of inoculation experiment of promoting bacteria and its ecological effect in field:Our research screening3strains which had a good effect on tomato and conducting the experiments ofpakchoi inoculation in field. It found that the effect of7087and161-2-13treatment is obvious; The soilphosphatase and invertase activity was significantly increased, but the activity of soil xylanasedecreased; Preliminary inspection the strains7209and161-2-13could colonize in rhizosphere soil andthe strains7087and7209could colonize in plant; The community structure of bacteria and diazotrophsin plant root and rhizosphere soil had changed. The community structure of bacteria in rhizosphere soilof7209and161-2-13treatment and in plant of7087and161-2-13treatment change greatly. Thecommunity structure of diazotrophs in rhizosphere soil of7087and7209treatment and in plant of7209and161-2-13treatment change greatly.Research of the isolation identification of endophytic diazotrophs and its biologicalcharacteristics in vegetables: Our research detect the endophytic diazotrophs from9plant rootsamples in5kinds of vegetables, found that the number of endophytic diazotrophs was diversified fromdifferent samplings in different locations. Our research isolated51strains and belonging to16genera,the Pseudomonas genus, Rhizobium genus, Arthrobacter genus, and Paenibacillus genus were dominantpopulations.42strains of endophytic diazotrophs detected the nitrogenase activity at some extent,9 strains were ACC deaminase-positive strains,7strains could dissolve inorganic phosphorus,10strainscould dissolve organic phosphorus, and5strains could dissolve two kinds of phosphorus,9strainscould antagonize the Sclerotinia sclerotiorum,10strains could antagonize the Gibberella zeae, and7strains could antagonize two kinds of fungal pathogens, but had more effect on Sclerotinia sclerotiorum.Research of nifH genetic diversity of endophytic diazotrophs in vegetables: In the51strains ofendophytic diazotrophs,22strains detect the nifH genes,21strains could detect the nitrogenase activity,and the nitrogenase activity of6strains were significantly higher than the Azotobacter chrooccum.According to the DGGE fingerprints of nifH gene from the9plant root samples and22strains, it foundthat the bacteria community composition was influenced by the sources and varieties of samples,6strains were the profiles of corresponding system, and3strains was the dominant profiles. Through theidentification results of advantage profiles, we found that the diazotrophs composition of tomato rootwas similar to the green peppers, beans and pakchoi root, but had a low similarity with cucumber rootsamples.