Isolement des souches de Pseudomonas spp fluorescents rhizosphériques à partir de sol agricole et évaluation de leur rôle dans la croissance végétale et le biocontrôle des phytopathogènes

Abstract

19 strains of fluorescent Pseudomonas sp. were isolated from the rhizosphere and rhizosphere roots of durum wheat and barley from different biotopes, these strains were screened in vitro for their plant growth-promoting activity and biocontrol against Fusarium oxysporum. From an in vitro bioassay of Lactuca sativa, 8 strains were selected as plant growth promoting rhizobacteria (PGPR). According to macroscopic, microscopic and physicochemical tests, the strains were affiliated with P.aeruginosa, P.fluorescens and P.putida species. These strains were tested for their ability to produce enzymes of agricultural interest, strains OD11, FR14, FR24, FR13 were all producing proteases, amylases, lipases. All isolates were studied for their antagonistic effect against Fusarium oxysporum by the dual plate assay. FR14 and FR15 showed significant inhibition of mycelial growth with a percentage inhibition of 52.72% and 41.81% respectively. Two antifungal metabolites (phenazines, pyrrolnitrins) were extracted from cultures of strains FR14 and FR15 by the use of thin layer chromatography (TLC). The Rf values obtained ranged from 0.6 to 0.62 for PHZ and lack of PLN. The phenazic extracts were re-tested for their antifungal activities against F.ox and Aspergillus niger, the results showed a greater inhibitory activity of the two pathogens of the extract of the FR14 strain with an I% of 23.63%. F.ox and 11.66% for A.niger. These observed results allow strains FR14 and FR15 to be potential biocontrol agents for a future application.