| Leek is a perennial Liliaceae Allium plant, possessing specified value in medicineand edible make it an economic crops. Due to extensive use of chemical fertilizer whileplanting process, the quality and taste of leek has been deteriorated, and so does theenvironment. This research used directional separation and enrichment method,14plantgrowth promoting rhizobacteria（PGPR） were isolated from the rhizosphere soil of leekwhich were grown in Shuangjing Town, Harbin Hulan District, Heilongjiang Province.Tested strains were identified via physiological and biochemical analysis,16S rDNAsequence analysis and colony morphology analysis. And the specific effects on the leekgrowth and the series related promotion traits have been measured. However, results ofabove tests laid a foundation for using rhizosphere bacteria as fertilizers, so that reducethe use of chemical fertilizers. In addition, there were two isolates not only can promotethe growth of leek but also can degradate phoxim, this carried on the exploration ofdeveloping biological bacterium reagent with the effect of degradating pesticides. Mainresults were as follows:1.14strains were isolated from rhizosphere soil of leek and they were screenedout by the medium contained ACC as the sole nitrogen source. Afterphysiological and biochemical analysis and16S rDNA analysis, the strainswere identified, respectively belong to Pseudomonas sp., Klebsiella sp.,Sphingobacterium sp., Acinetobacter sp., Herbaspirillum sp., Enterobacter sp.,Alcaligenes sp., Xanthomonas sp..2. Isolated strains possess the capacity to produce ACC deaminase, synthetizeindole acetic acid （IAA）, siderophore and phosphate solubilization. The ACCdeaminase activity of these PGPR ranges from high to low as j-6,1-7,1-5, c-4,j-1,3-2,2-3, nong-4, c-5, c-7,4-4,1-3, j-4and nong-3. Different concentrationof L-Trp didn’t influence the amount of IAA synthesized by2-3and3-2.1-7,4-4, nong-4and1-3synthesised more IAA when the the concentration of L-Trpup to500μg·mL-1. As the concentration of L-trp increased, the IAA producedby j-6,1-7,4-4, c-7and nong-4increased.1-3produced less IAA after theconcentration of L-Trp decreased to200μg·mL-1while the IAA production rapid increased in the condition contained L-Trp500μg·mL-1. However, j-6and1-7has the strongest ability of synthesising IAA in all concentrations ofL-Trp, respectively0.402,2.584,4.070,6.470,7.027mg（mL OD600）-1and0.707,1.439,2.215,3.439and5.712mg（mL OD600）-1. As to the ability of thesynthesis of siderophore of these rhizospheric microorganism, they can besequenced from stronger to weaker, e.i.1-3,1-5, nong-3, c-4, nong-4, j-1, j-4,4-4,1-7, c-7,2-3,3-2, j-6and c-5. In addition, their phosphate solubilizationwere also determianted, and1-3showed the strongest ability, following by4-4,1-7, j-6, c-5, c-7, j-4,1-5,2-3, j-1, nong-4, c-4,3-2, nong-3.3. All of the14PGPR possessed the ability of degradating phoxim pesticide.When the concentration of pesticides in medium were50mg·L-1, Nong-4showed the higher ability of phoxim degradation, and Nong-3performed therelative lower ability. After cultivated in culture for seven days, the finaldegradation rate of phoxim by Nong-3and Nong-4are73.653%and87.697%.The final degradation rate of phoxim after seven days in soil by Nong-3andNong-4are77.192%and84.303%. As a whole, Nong-4showed higher abilityof phoxim degradation than Nong-3.4. Dry weight, fresh weight and plant physiological indexes of the leek weremeasured, and the best promoter of these14strains under laboratory conditionwas evaluated, they were c-1and2-3. Tested bacteria all shows the ability ofpromoting leek growth under greenhouse condition, and2-3works best,followed by j-6. Compared with controls, the fresh weight and dry weight ofplants which were treated with2-3has repectively increased230.55%and179.64%. And compared plants treated with j-6and control, fresh weight anddry weight of the former has respectively increased181.19%and170.36%. |
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