Cell interactions between a nonpathogenic Fusarium oxysporum strain and root tissues of Eucalyptus viminalis

Silvio Gianinazzi,Christine Arnould,Vivienne Gianinazzi-Pearson,Maria-Isabel Salerno

doi:10.1007/s10327-004-0110-2

Abstract

Nonpathogenic isolates of Fusarium oxysporum can be successful antagonists of pathogenic forms of the same fungal species that commonly attacks crop plants. The characteristics that distinguish nonpathogenic from pathogenic forms are not well understood. In this study, the mode of root colonization of Eucalyptus viminalis seedlings by a nonpathogenic F. oxysporum strain is described at the ultrastructural level. Root systems of E. viminalis plants were inoculated with nonpathogenic F. oxysporum strain Fo47 in an in vitro model system. Changes in the occurrence of nonesterified and methyl-esterified pectins in colonized E. viminalis roots were evaluated by in situ immunolabeling using two monoclonal antibodies, JIM 5 and JIM 7. Modes of penetration and root colonization patterns in E. viminalis seedlings by the nonpathogenic fungus were similar to those described for pathogenic forms of F. oxysporum. However, root interactions differed in that the nonpathogenic fungus did not induce host tissue damage. No papilla-like appositions were observed in host cells in response to invading hyphae, which did not disrupt the host plasma membrane in many cases, suggesting that a biotrophic relationship was established. Root colonization by the nonpathogenic strain did not induce alteration in JIM 7 labeling of methyl-esterified pectin in E. viminalis cell walls, whereas nonesterified pectin was detected to a significantly greater extent in cell walls of roots colonized by the fungus. Pectin components decreased slightly only at points of hyphal contact with host cells. Because nonpathogenic strains utilize pectin in pure culture, host control over enzyme activity or production by the fungi may at least partly explain their compatible interactions with host tissues.

Highlights

Pathogenic and nonpathogenic forms of Fusarium oxysporum Schlechtend.:Fr. species are found in agricultural soils throughout the world (Armstrong and Armstrong 1981)
This suggests that differences between pathogenic and nonpathogenic F. oxysporum strains may reside at the cellular level of root interactions
Hyphae of the nonpathogenic F. oxysporum strain Fo47 growing along the surface of E. viminalis roots were frequently enclosed by a film of electron-opaque material

Summary

Introduction

Pathogenic and nonpathogenic forms of Fusarium oxysporum Schlechtend.:Fr. species are found in agricultural soils throughout the world (Armstrong and Armstrong 1981). Nonpathogenic F. oxysporum Fo47 can infect the root tissues of several plants, including E. viminalis, without causing tissue disorganization (Mandel and Baker 1991; Olivain and Alabouvette 1997; Postma and Luttikholt 1996; Salerno et al 2000), and it can protect eucalypt seedlings against a pathogenic strain of F. oxysporum (Salerno et al 2000). Light microscopic observations of the penetration and colonization patterns of E. viminalis root tissues by both pathogenic and nonpathogenic F. oxysporum revealed that there were no major differences between the strains. Tissue rapidly became disorganized in E. viminalis roots colonized by pathogenic F. oxysporum, whereas root tissues did not show signs of damage with progression of the nonpathogenic strain even 30 days after inoculation (Salerno et al 2000)

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