Isolation And Identification Of Endophytic Nitrogen-fixing Bacteria And Different Levels Of N On Nitrogen Fixation In Sugarcane

In order to investigate the biological nitrogen fixation (BNF) resources of sugarcane, to isolate and screen endophytic nitrogen fixing bacteria strains from sugarcane, and to study the effects of different nitrogen levels on BNF of sugarcane, sugarcane vatieties Q124, Co281 and B8 from Guangxi Sugarcane Research Institute were employed as the plant materials in the present study. Twenty one strains of endophytic bacteria with capacity of reducing acetylene (C₂H₂) were isolated from them. Several strains of endophytic bacteria were identified on the base of physiological characteristics, the 16S rRNA gene and the nif H gene cloning. Nitrogenase activity and polysaccharide(PS) in sugarcane treated with different levels of N were determined. The results showed as frollows:1. The bacterium strain L2 belonged to Klebsiella and the 16S rRNA gene sequence in full length was 1449 bp, the nif H gene sequence was 724 bp. The bacterium strain L3 belong to Enterobacteriaceae bacterium and the 16S rRNA gene sequence in full length was 1448 bp, the nif H gene sequence was 365 bp. The bacterium strain L4 belong to Klebsiella and the 16S rRNA gene sequence in length was 904 bp.2. The PS content in different treatments reached its highest level at the booming stage of sugarcane. It showed the highest PS content from July to September in B8, and from August to September in ROC22. The PS content in zero N level treatment was increased as compared to that in the 1/2 N treatment in B8. However, the PS content in zero N plants showed lower than that in the 1/2 N plants without virus-free treatment but with nitrogen fixing bacterium inoculation in ROC22.3. Sugarcane plants showed higher nitrogenase activity in the 1/2 N level than that in the zero N level. The plants without virus-free treatment and / or not nitrogen fixing bacterium inoculation showed lower nitrogenasa activity in the zero N level than that in the 1/2 N level in both the varieties of B8 and ROC22.4. There was considerable effect on the biological nitrogen fixation in the virus-free treatment via heating. The effect of nitrogenase activity was stronger in the virus-free treatment as compared to the control with nitrogen fixing bacteria inoculated and without virus-free treatment.5. There was high nitogenase activity in variety of ROC22.