Mycoparasitisme et symbiose endomycorhizienne: Influence des microorganismes de la mycosphere sur un champignon endomycorhizien

Abstract

Des zones d'interactions entre le champignon endomycorhizien (MA), Glomus intraradices et quelques microorganismes telluriques tels que Rhizoctonia solani, Pythium ultimum, Fusarium oxysporum, Trichoderma harzianum et Pseudomonas fluorescens ont ete etudies au microscope photonique grace a l'utilisation d'un systeme in vitro en Petri compartimente. Ces observations ont mis en evidence des phenomenes de parasitisme du champignon MA par F. oxysporum et T. harzianum. Par ailleurs, il a ete demontre par microscopie electronique a transmission que le champignon MA developpait un moyen de defense physique contre l'attaque de F. oxysporum. Enfin, les mecanismes infectieux impliques lors de l'invasion du Glomus par T. harzianum ont pu etre reconstitues de la facon suivante: (i) reconnaissance et penetration localisee de la paroi chez G. intraradices a l'aide d'enzymes hydrolytiques; (ii) proliferation marquee du champignon parasite a l'interieur de son hote; et (iii) sortie du champignon parasite des hyphes de G. intraradices.

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Areas of interaction between the endomycorrhizal fungus (AM), Glomus intraradices and some soil-borne microorganisms such as Rhizoctonia solani, Pythium ultimum, Fusarium oxysporum, Trichoderma harzianum and Pseudomonas fluorescens were studied using a light microscope using a system in vitro in a compartmented Petri. These observations highlighted phenomena of parasitism of the AM fungus by F. oxysporum and T. harzianum. Furthermore, it was demonstrated by transmission electron microscopy that the MA fungus developed a means of physical defense against the attack of F. oxysporum. Finally, the infectious mechanisms involved during the invasion of Glomus by T. harzianum could be reconstituted as follows: (i) recognition and localized penetration of the wall in G. intraradices using hydrolytic enzymes; (ii) marked proliferation of the parasitic fungus inside its host; and (iii) exit of the parasitic fungus from the hyphae of G. intraradices.