Efficacy of talc bio-based formulation of Bacillus amyloliquefaciens and Rhizobium gallicum for Phaseolus vulgaris L. seeds coating

The aim of this study is to evaluate the effectiveness of Bacillus amyloliquefaciens / Rhizobium gallicum - talc formulations to control fungal diseases and to promote plant growth in the common bean ( Phaseolus vulgaris L.). Bacillus amyloliquefaciens strain PVB17 and R. gallicum strain Ma1.12 inhibited Fusarium oxysporum , Alternaria alternata and Macrophomina phaseolina growth by up to 70% and 50%, respectively. Both bacterial strains are able to produce siderophores, indole-3-acetic acids (IAA), and exopolysaccharides. Interestingly, R. gallicum strain Ma1.12 IAA production reached 910 µg. mL ^− 1 , a value to be reported for the first time and has never been reported in various bacterial species. Talc was sampled from the region of Grombalia and powder was prepared. Gum Arabic was used as an adhesive in the bacterial formulation. The shelf life assessment- during two months of incubation- showed that B. amyloliquefaciens and R. gallicum strains are able to survive at more than 10 ⁸ cfu. g ^− 1 of talc formulation. Whether used separately or combined, coating common bean seeds with Ma1.12 and PVB17 strains and growing them in a peat/sand mixture resulted in a significant increase in shoot and root dry weights up to 200% and 400%, respectively. Interestingly, the biocontrol assay of a pathogenic F. oxysporum with the talc bacterial formulations is associated with a decrease in fungal incidence in plant growth. A Field trial conducted in the region of Boucharray showed that seed coating with the formulations of R. gallicum strain Ma1.12 and B. amyloliquefaciens strain PVB17 significantly increased plant growth, nodule number, and pod weight. Combined seeds-coating using both bacterial strains gave the highest increases in shoot dry weight (by 108%), nodules number (by 861%), and pods weight (by 209%) in comparison to the controls. Seeds coating with the bacterial formulation are associated with decreased disease symptoms.