Evaluation of the Endophyte Enterobacter cloacae SM10 Isolated from Spinach Roots for Biological Control against Fusarium Wilt of Spinach

Six hundred sixty-three isolates of microorganisms, including fungi and bacteria, were collected from surface-sterilized roots of spinach (Spinacia oleracea L.) growing in commercial greenhouses in Kyoto Prefecture. These isolates were screened for their ability to control Fusarium wilt of spinach caused by Fusarium oxysporum f. sp. spinaciae. In primary screening, spinach seeds were treated with the isolates, sown in pots containing sterilized soil, and then challenge-inoculated with the pathogen. Nine bacteria were effective in reducing disease incidence. Subsequently, spinach seeds were treated with the selected isolates, then sown in an infested field and grown from June to July 1998. Four bacteria reduced disease incidence. One of these four, designated as SM10, significantly suppressed the disease. Based on bacteriological properties, SM10 was identified as a strain of Enterobacter cloacae. SM10 was observed within xylem vessels of spinach roots using light and immunoelectron microscopy, indicating E. cloacae SM10 was an endophytic bacterium of spinach.