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).