Isolement de bactéries extrêmophiles d’intérêt agricole productrices de molécules antifongiques

Abstract

Salinity is one of the major factors responsible for the deterioration of soils, making them unsuitable for agriculture. The application of halotolerant and halophilic plant growth- promoting bacteria PGPR: Plant Growth Promoting Rhizobacteria) with biological control activities as crop inoculants offers a biological alternative to the use of , particularly when they are subjected to saline stress. To this end, 70 bacterial strains were from saline soils (sebkha) in arid and semi-arid zones of eastern Algeria. Three isolates were selected based on their production of bioactive molecules that promote plant growth. 100% of isolates have the capacity to fix nitrogen and produce ammonia (NH3). 53.33 % have the ability to solubilise inorganic phosphate, and 33.33% produce (HCN) and 6.67% produce IAA. Two of these isolates belong to the genus Serratia and the third is a halophilic Halomonas bacterium. These bacteria were identified based on the 16S rDNA sequence. Antagonism tests against phytopathogenic fungi were carried out. The antifungal molecules by these bacteria were identified using high- liquid chromatography. These bacteria are capable of inhibiting mycelial growth against fungi, with rates reaching 80.67% against Botrytis cinerea, 76.22% against Aspergillus niger and 66.67% against Fusarium culmorum for Serratia sp. The Halomonas sp. strain inhibited mycelial growth by producing volatile substances in 71.29% of niger, 75.49% of Aspergillus flavus and 72.22% of Penicillium glabrum. HPLC identification of the antifungal molecules by these three bacteria revealed that they , making these strains the first Rhizobacteria capable of phenolic compounds. Finally, pot tests were carried out to determine the effectiveness of these strains inpromoting wheat growth under salt stress (125 mM, 150 mM and 200 mM). The results showed that a consortium of two isolates (Serratia sp.-SB6 et Halomonas sp.-SB39) gave the best results at 125 mM with a significant increase in plant height of 30% on sterile soil and 46% on non-sterile soil. However, at higher concentrations, the halophilic sp bacteria gave the best results. In all cases, a significant improvement in the growth of wheat seedlings inoculated with the bacteria was observed compared to the non-inoculated .