Plant phenotyping
After surface sterilization, seeds of Arabidopsis and Broccoli were pre-germinated on sterile wet filter paper in plastic petri dishes and placed at 4 °C in the dark for 4 and 2 days, respectively. After emergence of the radicle, seeds were sown on half-strength Murashige and Skoog (MS) medium containing 2.5% (w/v) sucrose and plant agar 1,2%. The plates were then transferred to a climate chamber at 21 °C /21 °C day/night; 180 µmol light m-2s-1, 16h light/8h dark cycle and 70% relative humidity. The root tips of the seedlings were inoculated with 2 µL of washed bacterial cell suspension (OD600 = 1.0) 7 days post planting for A. thaliana and A. annua and after 3 days for B. oleracea ; the plants were grown in the same growth chamber until harvest. To assess the temporal changes in plant growth of the different plant species-rhizobacteria combinations, the shoot fresh biomass was determined every two days until 11 days post inoculation (dpi) for Arabidopsis and Broccoli and until 14 dpi for Artemisia. For each plant species, four independent biological replicates were considered with 10 seedlings of Arabidopsis, 8 of Artemisia and 5 of Broccoli per biological replicate. Prior to root dry mass measurements, roots were carefully detached from the MS-agar and washed with sterile distilled water to remove agar. Thereafter, root dry biomass was determined (Ostonen et al. 2007).