Control of damping-off caused by Rhizoctonia solani and Fusarium solani using olive mill waste water and some of its indigenous bacterial strains

Olive mill waste water (OMW) and some of its indigenous bacterial strains were tested in vitro and in vivo for their efficacy against damping-off caused by two soilborne fungi Rhizoctonia solani and Fusarium solani. OMW and polyphenols displayed a high level of antifungal activity against R. solani. However, F. solani was more resistant and only the highest dose (2%) prevented its mycelial growth. In pot experiments, the percentage of tomato plants showing symptoms of damping-off was significantly reduced with different doses of OMW (0.5%, 1% and 2%) as compared to the control (soil treated with water). Nine indigenous bacterial strains isolated from OMW exhibited an antagonistic effect against the two fungi. Based on the gene 16S rRNA sequence analysis, four isolates showed 99.2% similarity to known sequences of Bacillus subtilis, three isolates demonstrated low percentage similarities (94.3–96.5%) to the genera Bacillus, whereas two isolates were associated with Burkholderia caryophylli and Pseudomonas fluorescens (98.2–99.6% similarities). Among these bacteria, the strain B1 proved efficient against the two soilborne pathogens in vitro and in pot experiments.Our study in controlled conditions suggested that addition of OMW to soil exerts significant disease suppressiveness against R. solani and F. solani.