植物根面における病原性および非病原性<I>Fusarium oxysporum</I>の増殖比較

Abstract

In the present study, a green fluorescence protein (GFP) gene was introduced as a monitoring reporter into mycelial protoplasts of different formae speciales of Fusarium oxysporum (lycopersici, melonis and fragariae) to analyze infection behavior of pathogenic and nonpathogenic fungi on roots of host and nonhost plants. Successful integration of the GFP gene into chromosome was confirmed by polymerase chain reaction and Southern hybridization analysis. GFP-marked fungi emitted bright green fluorescence under UV irradiation. Transformed microconidia of F. oxysporum were inoculated by dropping conidial suspension onto roots of tomato and melon cotyledonal seedlings. Fungal development on roots was observed with a fluorescence microscope at the post-inoculation stage (1 to 3 days after inoculation). As a result, the microconidia of all formae speciales germinated and attached to root surface and elongated hyphae to reticulate root surface, irrespective of host and nonhost plants. After this reticular elongation of hyphae, the pathogenic fungi on host plant roots invaded to cause necrosis at the inoculation site of roots. Thus, the present results demonstrated that both pathogenic (F. oxysporum f. sp. lycopersici on tomato) and nonpathogenic fungi (F. oxysporum f. sp. fragariae on tomato and melon, and F. oxysporum f. sp. melonis on tomato) could indistinctively elongate hyphae and colonize host and nonhost plant roots at the early stage of inoculation, and only the pathogenic fungi invade host roots to cause the symptoms after mycelial colonization.