The PSB population density was assessed by the pour plate method.
The rhizosphere soil was collected by uprooting the plants. Soil adhering to the roots was serially diluted (102 to 106) with 0.85% NaCl solution and aliquots from 0.1 mL of the sample from each of these dilutions were spread on a petri dish containing NBRIP medium.
Plates were incubated 3 d in an incubator at 30 °C.
Colonies with clear halos were counted at the end of the incubation period.