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

AUTOR(ES)

Benhamou, Nicole

FONTE

American Society for Microbiology

RESUMO

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.

Documentos Relacionados

• Antagonistic Effect of Nonpathogenic Fusarium oxysporum Fo47 and Pseudobactin 358 upon Pathogenic Fusarium oxysporum f. sp. dianthi
• Effect of pseudobactin 358 production by Pseudomonas putida WCS358 on suppression of fusarium wilt of carnations by nonpathogenic Fusarium oxysporum Fo47.
• Overexpression of an endogenous thionin enhances resistance of Arabidopsis against Fusarium oxysporum.
• Resistance of common bean to Fusarium oxysporum f. sp. phaseoli.
• Multiple AGAMOUS homologs from cucumber and petunia differ in their ability to induce reproductive organ fate.