Abstract:
Various Azotobacter cultures were isolated from the rhizosphere of maize. Ten fast growing cultures were selected (numbered as Zi, Zi, Zie), and evaluated for their potential to produce auxins (lAA-equivalents) in vitro both in the absence and presence of auxin precursor, L-tryptophan (L-TRP). Azotobacter cultures varied in their auxin producing ability and Z' was the most efficient auxin (3.1 fig lAA-equivalents mL') producer in the absence of L-TRP. Supplementation of the medium with L-TRP @ Iff1 and lfr'M stimulated auxin production by almost 2-fold over the unamended control. Various environmental factors strongly affected I.-TRP-dependent auxin biosynthesis in soil, and optimal productions were found at 6.0 mg L-TRP g'' soil, 6.0 mg glucose g~'
soil, pH7.0, 40 °C temperature, shaking @ of 150 rpm, no nitrogen and 48 hours of incubation. Application of antibiotics (streptomycin or erythromycin) had inhibitory effects on auxin biosynthesis in soil.
