Localisation des déterminants de la suppression de quelques souches de pseudomonas isolées de la rhizosphère de la pomme de terre

Abstract

A total of 65 isolates of fluorescent Pseudomonas spp. have been isolated from various rhizospheric soils which were cultivated or received a potato culture, which constitute two different habitats. Pseudomonas aeruginosa, P. fluorescens, P. putida and P. chlororaphis present the species types that were found with a predominance of P. fluorescens. This result confirms once again the ubiquity and adaptability of this bacterial group particularly in the rhizosphere. The trophic profiles of the isolates showed a considerable diversity within their carbon metabolism, which resulted in a divergence between the trophic profiles and the identification results. It seems that the biotopes significantly affect the distribution of isolates and probably select this isolates according to their trophic profiles. Among these isolates, producers of secondary metabolites (such as bacteriocins, siderophores, hydrogen cyanide, phosphatases, salicylic acid, indole acetic acid, phenazines ........), some showed an antagonistic capacity in vitro against many bacterial agents and phytopathogenic fungy. The antagonistic function, the promotion of plant growth, the rhizosphere competence and antibiotic resistance have been reported. These characters were found in the rhizosphere isolates. However this rhizospheric competence is better expressed in a natural soil than in the sterile soil. Field testing conducted in a natural soil with different isolates showed that these isolates protect the plants affected with pathogens to varying degrees especially against vascular fusariosis, by reducing the incidence and symptoms of the disease and stimulating plant growth. This is correlated with the metabolic and the rhizospheric competences of the isolates.