Abstract: ObjectiveThe infection and colonization of nitrogen-fixing bacteria DX120E in sugarcane seedlings and the effects on the growth and physiology in different sugarcane varieties were studied to provide reference for further ana-lysis of the interaction mechanism between nitrogen-fixing bacteria and sugarcane.MethodSugarcane varieties ROC22, GT21 and B8 were used as test materials. After DX120E was labeled with gfp gene,sugarcane was inoculated by root-soaking method,and infection and colonization of DX120E in sugarcane were observed. The plant height,chlorophyll content and fresh weight of sugarcane were investigated at 60,90 and 120 d after inoculation,and the key enzyme activi-ties of nitrogen metabolism were measured.ResultStably expressed DX120E-gfp zygote strains was obtained. On day 7 after inoculation,nifH gene expression was detected in the roots and leaves of three sugarcane varieties,and the fragment size was approximately 360 bp. The results of fluorescence microscopy showed that on day 7 after inoculation,nitrogen-fixing bacteria was colonized in the root hair zone,the neonatal lateral roots,the root fracture wounds and the cross-sec- tions of the leaves of sugarcane. Pot experiment showed that compared with the control of inoculation with no nitrogen-fixing bacteria,the sugarcane inoculated with nitrogen-fixing bacteria DX120E could effectively promote the growth of the three varieties. And 120 d after inoculation,the plant heights of ROC22,B8 and GT21 respectively increased by 23%,20% and 14%;the fresh weight of aboveground increased by 25%,31% and 11% respectively;the fresh weight of under-ground part increased by 40%,34% and 30% respectively. The activity of glutamine synthetase and nitrate reductase in leaves of the three sugarcane varieties was also higher than that of the control.ConclusionBy using the root-soaking method to inoculate sugarcane,the nitrogen-fixing bacteria strain DX120E can colonize the roots and transfer to the leaves of sugarcane. Using this method to treat sugarcane has obvious promoting effects on sugarcane,but there are some differences between different varieties.