Ability of Nonpathogenic Fusarium oxysporum Strain Fo47 To Induce Resistance against Pythium ultimum Infection in Cucumber

Abstract

The influence exerted by nonpathogenic Fusarium oxysporum strain Fo47 in triggering cucumber protection against infection by Pythium ultimum was investigated ultrastructurally. Macroscopic and microscopic observations of the pathogen colony in dual cultures revealed that reduction of Pythium growth was associated with marked disorders, including generalized disorganization of the host cytoplasm, retraction of the plasmalemma, and complete loss of the protoplasm. Cytochemical labeling of cellulose with an exoglucanase-gold complex showed that the cellulose component of the host cell walls was structurally preserved at a time when the host cytoplasm had undergone complete disorganization. A similar antagonistic process was observed at the root cell surface. Most striking and interesting was the finding that mycoparasitism, as evidenced by the frequent occurrence of Fo47 hyphae within nearly empty cells of the pathogen, occurred not only at the root surface but also within the invaded root tissues. The specific labeling pattern obtained with the exoglucanase-gold complex confirmed that Fo47 successfully penetrated cells of the pathogen, both in the rhizosphere and inside the root tissues. Pythium cells that could evade the first defensive line in the rhizosphere could penetrate the root epidermis, but their growth was restricted to the outermost tissues. Positive correlations between Fo47 treatment and induced resistance to infection by P. ultimum in cucumber were confirmed by (i) the reduction of pathogen viability; (ii) the elaboration of newly formed barriers, a phenomenon which was not seen in Fo47-free plants, where the pathogen proliferated in all root tissues within a few days; and (iii) the occlusion of intercellular spaces with a dense material likely enriched in phenolics. Taken together, our observations provide the first convincing evidence that Fo47 exerts a direct inhibitory effect on P. ultimum through a combination of antibiosis and mycoparasitism, in addition to being a strong inducer of plant defense reactions.

Pythium oligandrum: an example of opportunistic success

“…An approach combining P. oligandrum with two other well-documented biocontrol agents (T. harzianum and Fusarium oxysporum, strain Fo47; Benhamou et al, 2002;Harman, 2006), reveals that P. oligandrum successfully colonizes the rhizosphere and is able to penetrate the root system (Le . Additionally, the observations indicate that P. oligandrum, alone or in combination with the two other antagonists, is similarly effective at reducing grey mould incidence in tomato plants infected by B. cinerea and that this increased protection apparently correlates with an overexpression of protein PR-3 (chitinases).…”

Priming by Rhizobacterium Protects Tomato Plants from Biotrophic and Necrotrophic Pathogen Infections through Multiple Defense Mechanisms

“…Virulent pathogens induce rapid cellular defense responses such as AOS accumulation, callose and phenolic compound deposition, and augmented transcriptions of defense-related responses in plants primed by PGPR (Benhamou et al, 2002;Faize et al, 2004;Jeun et al, 2004;Pare et al, 2005;Park et al, 2002;Verhagen et al, 2010;Whipps, 2001;Yedidia et al, 2003). Besides arresting pathogen proliferation in planta, AOS are involved in cell wall fortification (Olivain et al, 2003) and protein cross-linking, and acts as signaling molecules mediating systemic resistance.…”

Fusarium oxysporum (F221-B) as biocontrol agent against plant pathogenic fungi in vitro and in hydroponics

“…antibiosis and competition. Unlike F221-B in our study, most of the non-pathogenic F. oxysporum strains which have been so far reported as promising BCA against fungal pathogens were isolated only from rhizosphere soils and roots of plants grown in suppressive soils (Benhamou et al 2002;Fravel et al 2003;Abeysinghe 2006;Rodriguez et al 2006;Patil et al 2011) but not from hydroponics. However, these results of the antagonistic activity and mechanisms of F221-B were still in line with those findings.…”

“…direct inhibitory effect on Pythium ultimum through a combination of antibiosis and mycoparasitism (Benhamou et al 2002) and the non-pathogenic S6 had a marked antagonistic capacity against the pathogen sclerotinia sclerotiorum with the responsible metabolite cyclosporine A (Rodriguez et al 2006). …”