SEM (scanning electronic microscopy),LSCM (laser scanning confocal microscope) and GFP (green fluorescent protein) techniques were used to study the endogeneity and colonization rules of Bacillus pumilus strain LYMC-3,which has high nematicidal activity.The shuttle vector pGFP78 carrying gfpmut3a gene,was transformed into B. pumilus strain LYMC-3 for fluorescence-tagging by nature transformation and expressed successfully.The plasmid stability was then determined.After inoculating the bacteria in root surface of masson pine,the colonization of LYMC-3 tagged with GFP was studied by combining antibiotics plate recovery and LSCM.GFP-tagged LYMC-3 with bright green fluorescence was observed under 481 nm wavelength and the genetic stability was 96.8% after 8 continuous dilution culture.On 4th day after inoculation in masson pine root,a large number of labeled strains were recovered,followed by a downward trend,and the number decreased faster in the root than in the stem.On 40th day after inoculation,the number of the labeled strain was 0.3×102 cfu/g in the root,and 0.8×102 cfu/g in the stem.These results demonstrated that the tagged strain could successfully colonize and transmit in masson pine,which provide a scientific basis for the exploitation and utilization of strain LYMC-3.