Isolation Of Fluorescent Pseudomonas Spp. Strains From Rhizosphere Agricultural Soils And Assessment Of Their Role In Plant Growth And Phytopathogen Biocontrol
Résumé: Plant Growth Promoting Rhizobacteria , PGPR are the rhizosphere bacteria that can enhance plant growth. The exploitation of the PGPR in sustainable agriculture as biopesticides / biofertilizers has became a real alternative for agrochemicals used as environment friendly agriculture. In the rhizosphere, Pseudomonas spp. are an important and abundant group affecting plant growth. From diverse agro-ecosystems of Algeria. In this study, 19 fluorescent strains of Pseudomonas spp were isolated from the rhizosphere roots and soils of durum wheat and barley from different biotopes, these strains were screened in vitro for their plant growth promoting activity and the biocontrol of phytopathogenic fungi. From an in vitro bioassay of Lactuca sativa, 8 strains were selected as PGPR. According to phenotypic identification, 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 of which OD11, FR14, FR24, FR13 have been producing proteases, amylases, lipases. The 8 isolates were studied for their antagonistic power against Fusarium oxysporum. 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 thin layer chromatography. The Rf values obtained ranged from 0.6 to 0.62 for PHZ and absence of PLN. The phenazic extracts were re-tested for their antifungal activities against Fusarium.oxysporum and Aspergillus.niger, the results showed an important inhibition of pathogens by the extract of the strain FR14 with a percentage of inhibition of 11.66% to 23, 63%. These results allow FR14 and FR15 strains to be potential biocontrol agents for a future application. Understanding on the diversity of a most important genus of PGPR in the rhizosphere and mechanism of action should facilitate their application as a reliable component in the management of sustainable agricultural system.
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