Confocal laser scanning micrographs of the colonization of GFP-tagged N43 on the roots of cucumber seedlings 2 weeks after inoculation. (A) The control, which was not inoculated with GFP-tagged N43. (B) The positive control, which was soaked in 108 cells of GFP-tagged N43 per ml prior to observation. (C)–(F) The roots from the soils inoculated with 105, 106, 107 and 108 cells of GFP-tagged N43 per g soil, respectively.