Effects Of Co-inoculation PGPR And Rhizobium On Growth Of Alfalfa Under Saline-alkali

The growth of plants and soil fertility were seriously influenced by saline-alkali stress.The symbiotic fixation of rhizobium with plant could provide the source of nitrogen,alleviate the saline-alkali stress,which can play an important role in biological improvement.However,under various soil conditions,single rhizobium still have some problems such as the less of environment suitability,low efficiency of nodulation competition and the effect of promoting growth is not ideal.In the present study,we used cfp(cyan fluorescent protein)marked alfalfa rhizobium,co-inoculated PGPR(plant growth-promoting rhizobacteria)and rhizobium combinations were selected by antagonistic reaction,the characteristics of growth-promoting of selected strain combinations were evaluated,and investigate the effect of alfalfa using selected PGPR and rhizobium strain combinations under saline-alkali stress.The study laid the foundation of the development of new bio-fertilizer.The main results were as follows: 1.Construction of cfp fluorescent marked rhizobiumUsing the tri-parental mating method,the marked S.meliloti A10-1 with cfp gene,denoted as A10-1cfp has been successfully obtained.A10-1cfp in pure culture and symbiotic conditions could all stably express cyan fluorescent protein.2.Screen of co-inoculated PGPR and rhizobium strain combinationsThe combination of six PGPR and cfp marked rhizobium A10-1cfp were selected by antagonistic reaction.Then five co-inoculated PGPR and rhizobium strain combinations were selected based on alfalfa seed germination tests under saline-alkali stress and the analysis of saline-alkali tolerance.The five strain combinations were A10-1cfp+nong-4,A10-1cfp+J-6,A10-1cfp+MN-5,A10-1cfp+MY-5,and A10-1cfp+CE-1.3.Characteristics of growth-promoting of the co-inoculated PGPR and rhizobiumCompared with single strain,the ability of the co-inoculated PGPR and rhizobium strain combinations were enhanced on ACC deaminase,IAA,inorganic phosphorus solubilization and nitrogen fixation.The ACC deaminase of co-inoculated strain combinations A10-1cfp+J-6,A10-1cfp+nong-4 were significantly increased compared with single strain(P < 0.05).When the L-Trp concentration was 500 μg/mL,the IAA contents of A10-1cfp+nong-4,A10-1cfp+J-6,A10-1cfp+MN-5,A10-1cfp+MY-5 and A10-1cfp+CE-1 were significantly increased than the single strain(P < 0.05).The PGPR and rhizobium strain combinations A10-1cfp+nong-4 and A10-1cfp+CE-1 showed higher phosphorus solubilizatin abilities compare with single strain(P < 0.05).In terms of nitrogen fixation,except A10-1cfp+MN-5,the other strain combinations showed higher nitrogen fixation compared with single strain(P < 0.05).4.Effect of growth-promoting by co-inoculated PGPR and rhizobium strain combinationsCompared with the non inoculated strains(Control),single strain and co-inoculated PGPR and rhizobium strain combinations could promote alfalfa growth in different extent.The significantly increased effect of plant growth promotion were found in co-inoculated PGPR and rhizobium strain combinations A10-1cfp+nong-4,A10-1cfp+J-6,A10-1cfp+MN-5,A10-1cfp+MY-5 and A10-1cfp+CE-1(five PGPR and rhizobium strain combinations)(P < 0.05).The dry weight shoot were increased by 73.12%,64.52%,40.86%,30.11% and 49.46% respectively,and the dry weight of root were increased by 97.06%,85.29%,79.41%,52.94% and 70.59% respectively.In terms of alfalfa nodule and rhizobium nodule occupancy rate,compared with single strain,the nodule number and nodule fresh weight per plant of alfalfa inoculated with PGPR and rhizobium strain combinations were significantly increased;the analysis of the cfp marked rhizobium nodule occupancy rate showed that,compared with A10-1cfp alone,five PGPR and rhizobium strain combinations were increased by 12.1%,8.5%,5.1%,3.5% and 5.3%.In terms of the quality of nutrition,compared with control,co-inoculated PGPR and rhizobium strain combinations A10-1cfp+农-4 increased crude protein and phosphorus content of alfalfa,the protein content is 18.38%,and the content of phosphorus increased the most.In terms of the chlorophyll content of alfalfa,PGPR and rhizobium strain combinations A10-1cfp+nong-4,A10-1cfp+J-6,A10-1cfp+MY-5 were significantly increased than inoculation alone group(P < 0.05).