Colonization of tomato root by a non‐pathogenic strain of Fusarium oxysporum

Abstract

SUMMARYA strain of non-pathogenic Fusarium oxysporum Schlecht. emend, Snyd. & Hans, has been selected for its capacity to reduce the incidence of Fusarium wilt of tomato. Among the possible modes of action of this strain, competition with the pathogen for the colonization of the root surface and tissues has been proposed, in order to study the pattern of root colonization, young Lycopersicon esculentum Miller (tomato) plants grown in a nutrient solution were inoculated by a suspension of F. oxysporum microconidia and processed at time-intervals for microscopic observations. The fungal strain was transformed with the Gus reporter gene to facilitate the observations. Within 24 h of inoculation the root surface was colonized by a dense network of hyphae, with the exception of the apex, which was colonized only after 48 h. A few hyphae were observed penetrating into the epidermis, leading to the internal colonization of the root cortex. This colonization was always discontinuous, since defence reactions of the plant limited the extension of the fungus. The barrier formed by thickenings and coilings of the cell walls and hypertrophied cells was most frequently observed in the external cortex and, sometimes, deeper in the internal cortex, close to the vessels which were never colonized. Typical defence reactions such as wall appositions, intercellular plugging and intracellular osmiophilic deposits, were frequently observed. This is the first report, based on microscopic observations, of the capacity of a non-pathogenic strain of F. oxysporum to colonize roots of tomato.

Effects on growth and comparison of root tissue colonization patterns of Eucalyptus viminalis by pathogenic and nonpathogenic strains of Fusarium oxysporum

“…The fact that F. oxysporum strain Fo47 colonized the same root tissues as strain Foeu1 in E. viminalis shows that both nonpathogen and pathogen occupy the same ecological niche, and suggests that competition for infection sites might be one of the modes of action involved in bioprotection by strain Fo47, as also evoked by Olivain & Alabouvette (1997. Furthermore, Paulitz et al (1987) have proposed that, in general, nonpathogenic Fusarium isolates are efficient biocontrol agents because they are highly competitive saprophytes and successfully colonize the cortical tissue of roots.…”

“…Furthermore, Paulitz et al (1987) have proposed that, in general, nonpathogenic Fusarium isolates are efficient biocontrol agents because they are highly competitive saprophytes and successfully colonize the cortical tissue of roots. However, competition for infection sites alone does not necessarily fully explain all the biocontrol activity of nonpathogenic strains of F. oxysporum (Olivain & Alabouvette, 1997). The presence of the pathogen F. oxysporum f. sp.…”

“…Nonpathogenic or less virulent Fusarium species have been reported to suppress the development of several forms of F. oxysporum in different crops (Alabouvette et al, 1987 ;Cugudda & Garibaldi, 1987 ;von Mattusch, 1990). The mechanisms by which nonpathogenic strains of F. oxysporum suppress diseases are not well understood (Olivain & Alabouvette, 1997) and those cited include nutritional, saprophytic and\or parasitic competition (Alabouvette et al, 1979 ;Schneider, 1984 ;Lemanceau, 1989), as well as the possible existence of induced resistance (Olivain et al, 1995 ;Duijff et al, 1997 ;Duijff et al, 1998).…”

“…Knowledge of the patterns of root colonization by pathogenic and nonpathogenic isolates of F. oxysporum could contribute to an understanding of the mechanisms of disease suppression (Olivain & Alabouvette, 1997 and might help to improve the success of biological control.…”

Process of tomato root colonization by a pathogenic strain of Fusarium oxysporum f. sp. lycopersici in comparison with a non‐pathogenic strain

“…However, most of the strains are termed non-pathogenic because they are unable to induce disease on a given plant species. Nevertheless, they are parasitic because they colonize the root tissues of the plant to some extent (Nagao et al, 1990 ;Mandeel & Baker, 1991 ;Postma & Luttikholt, 1996 ;Olivain & Alabouvette, 1997). The *Author for correspondence (fax j33 3 80 69 32 26 ; e-mail alabouvette!dijon.inra.fr).…”