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To the authors' knowledge, most studies on biofilm formation have focused on bacteria and yeasts. So far, biofilm formation by fungal plant pathogen has not been reported. In this study, the biofilm-forming capacity of Fusarium oxysporum f. sp. cucumerinum was evaluated. For biofilm quantification, a colorimetric 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2 H-tetrazolium-hydroxide ( XTT) reduction assay was used to observe metabolic activity. Fluorescence and confocal scanning laser microscopy revealed that the biofilms have a highly heterogeneous architecture composed of robust hyphae and extracellular polysaccharide materials. Additionally, the influence of physical factors on F. oxysporum biofilm formation and the susceptibility of biofilms to environmental stress was investigated. Biofilms were less susceptible to heat, cold, UV light and three fungicides than were their planktonic counterparts. Our findings may provide a novel perspective on the pathogenic mechanism associated with biofilms of F. oxysporum f. sp. cucumerinum. [ABSTRACT FROM AUTHOR]