Study On Plant Growth-promoting Activity Of Cotton Rhizosphere Bacteria

In this study, the plant growth promoting traits of29strains which had an efficient affinity staining on cotton lectin were measured, and their practical effect on the growth of cotton were also detected. By comparing the two data, we want to devise a evaluation system by which we can get strains that can fixing nitrogen, dissolving phosphorus efficiently, and these strains may also have the ability to inhibit pathogenic microorganisms.The plant growth promoting traits of PGPR has a significant impact on the growth of plants. So it is necessary to identificate the plant growth promoting (PGP) traits of strains, such as production of IAA and siderophores, phosphorus solubilization, ACC deaminase as well as inhibition to fungi pathogens. The results showed that all the29strains could secrete IAA and had exhibited the ability to solubilize phosphate. The secretion of IAA arranging from0.15to26.87mg/L, and the activity of solubilizing phosphate of the29strains arranging from8.41to27.67μg/mL. Three isolates produced more than20mg/L IAA, those are P1103(Pseudomonas sp.), P211(Xanthomonas sp.) and P2107(Pseudomonas sp.).9nitrogen-fixing strains and8phosphate solubilizing strains secreted IAA arranging from1to4mg/L, other strains secret IAA below1mg/L. Strains N3101(Azotobacter sp.) showed the lowest amount of solubilized phosphate, which was8.406mg/mL. The amount of solubilized phosphate to the other28strains were all higher than10μg/mL. All the isolates produced siderophores by using CAS reaction except nitrogen-fixing bacteria N1111(Azotobacter sp.), with P2107(Pseudomonas sp.) has the highest production of siderophores, up to the level of5+.46.67%of the strains achieved a high level production of siderophores. P211(Xanthomonas sp.) and P2107(Pseudomonas sp.) had the ability to secreted ACC deaminase, the specific activity of the two phosphate solubilizing strains were0.068U/mg and1.016U/mg. N1105(Derxia sp.), P1108(Pseudomonas sp.) and P2107(Pseudomonas sp.) showed the ability to inhibit cotton fusarium wilt(Fusarium.Oxysporum), with inhibition efficiency of35.51%,42.24%and32.14%.Pot experiment was used to determine the promoting effect of29strains on the growth in cotton. The results shows that3nitrogen-fixing strains and4phosphate solubilizing strains promoted the shoot length while4nitrogen-fixing strains and5phosphate solubilizing strains increased cotton dry weight. Comparing to the total fertilization contorl, P1108(Pseudomonas sp.) increased the shoot dry weight, root dry weight, root length and root activity of cotton, the dry weight increased27.70%. The phosphate solubilizing strains P2117(Acinetobacter sp.) increased shoot dry weight, root dry weight, root length and root activity of cotton, comparing to the two fertilization contorl, the dry weight increased38.17%. The nitrogen-fixing strains N1105(Derxia sp.) and N1111(Azotobacter sp.) promoted the dry weight of cotton, the dry weight increased45.03%and36.21%. Other stains had no obvious promotion effect on cotton.The all promotions mentioned above reached significant difference at p<0.05level.