Isolation, Biochemical Characterization and Biocontrol Potential of Soil Rhizospheric Bacteria of Vitis Vinifera L. On the Center of Tunisia

The soil is the main reservoir of bacteria. Their role could be beneficial or not and soil bacteria fulfill both roles and are ubiquitous. The primary purpose of this study was to assess the relationship between physicochemical soils properties (pH, electrical conductivity (EC), water content (WC), organic matter (OM), Dry matter (DM), Nitrogen (N)) and distribution of bacteria population, isolated in three different media: Nutrient Agar (NA), King B (KB) and International Streptomyces Project-2 (ISP2), in Tunisian vineyards. Thirty-one vineyards fields located at Sidi Bouzid region and cultivated with different 12 varieties of Vitis vinifera L. were studied. We tested the plant-growth-promoting (PGP) traits of 12 bacterial isolates like the production of indole acetic acid (AIA), phosphate solubilization (PS), atmospheric nitrogen fixation (ANF), pectinase production (PP), amylolytic activity (AA), proteolytic activity (PA) and catalase (Cat). The antifungal activity against phytopathogenic fungi Botrytis cinerea was assessed under laboratory conditions by the dual confrontation method. Soil bacteria analysis from vineyards showed remarkable diversity with a total number of 537 isolates. The colony-forming units (CFU) was ranged from 6.24 103 CFU/g soil for the Super Seedless variety to 5.66 104 CFU/g soil for the Sultanine variety (NA medium) and from 4.24 103 CFU/g soil for the Super Seedless variety to 2.83 104 CFU/g soil for Sultanine variety (KB medium), and varied from 4.09 103 CFU/g soil for Super Seedless variety to 2.42 104 CFU/g soil for Victoria variety (ISP2 medium). The PCA for spore-forming bacteria accounted for 69.59% of the total variability. A positive correlation was noted between the bacteria population, and both OM and WC. The exposed PGP tests enabled the retention of 11 isolates. Three bacterial isolates (k2Rh30, k2Rh9 and H3Rh4) possessed the highest antifungal potency against B. cinerea with an inhibition rate above 54.76%. It is concluded that the tested isolates have the potential for grapevine grey mold management to substitute synthetic fungicides. Nevertheless, further studies are mandatory to confirm their effectiveness.