Assessment of antagonistic activity of fluorescent pseudomonads isolated from potato rhizospher towards Ralstonia solanacearum under greenhouse conditions

This study was conducted to evaluate of the antagonistic activity of fluorescent pseudomonads against Ralstonia solanacearum in greenhous. A total of 80 strains of fluorescent pseudomonads were isolated from the soil around the healthy potato roots and tubers collected from 10 farms on King, s B medium (KB). The bacterial R. solanacearum strains were isolated on nutreient agar (NA) medium containing triphenyltetrazolium chloride (TTC). Antagonistic activity of pseudomonads strains was evaluated in a completed randomized design with three replicates in vitro. The bacterial strains EH87 and EH203 with 3.78 and 3. 65 cm growth inhibition zone were the most effective and EH27 and EH40 strain with 1. 85 and 1.54 cm had the least effect. The phenotypic feature of the antagonistic representative’s strains and their hypersensitive reaction on tobacco leaf showed that they were belonged to Pseudomonas putida and P. fluorescens (bv. I, II & IV). Based on the result of laboratory experiment nine representative strains were selected for further studies in a randomized design under greenhouse condition. After three months, growth factors of the plants and disease severity were measured and recorded. Results showed that EH70, EH49 bacterial strains had a high biocontrol effect in compare to contaminated control. They reduced the potato wilt disease caused by R. solanacearum 84% and 75% respectively. Total DNA from antagonistic representaives strains were used as a template to amplify 16SrRNA encoding gene using universal primers in PCR. Results showed that the strain EH53 had 98 percent sequence similarity to Pseudomonas fluoresens.