The productions of indole acetic acid (IAA) by the isolates were
determined following the method of Bric et al. (1991). A 48 h old
test bacterial culture grown on NGA-plate was inoculated into
nutrient broth supplied with 3 mM tryptophan and incubated at
28 C for 48 h. Bacterial cells were centrifuged at 3000 rpm for
30 min. 2 mL of the supernatant were mixed with 100 lL of
ortho-phosphoric acid and 4 mL of Solawaski’s reagent (50 mL
35% perchloric acid; 1 mL 0.5 M FeCl3) and incubated for 30 min.
Development of a pink color indicates IAA production. The pink
color was quantified using a spectrophotometer (Beckmann
DU640, USA) at 535 nm. The concentrations of IAA produced by
isolates were determined using a standard curve prepared from
pure IAA.
2.6. Ad planta