PRODUCTION OF INDOLE ACETIC ACID BY FLUORESCENT PSEUDOMONAS IN THE PRESENCE OF L-TRYPTOPHAN AND RICE ROOT EXUDATES

A total of 30 fluorescent Pseudomonas isolates (15 P fluorescens and 15 P aeruginosa) were obtained from different plant rhizospheres and were characterized on the basis of biochemical tests and plant growth-promoting activities. Pseudomonas fluorescens AK1 and Pseudomonas aeruginosa AK2 showed the best plant growth-promoting activity. These isolates were tested for their ability to produce indole acetic acid in pure culture in the absence and presence of L-tryptophan at 50, 100, 200 and 500 mu g/ml. For both strains, indole production increased with increases in tryptophan concentration (05, 1.2, 4.3 and 9.3 mu g/ml; and 0.2, 0.7, 3.8, and 8.3 mu g/ml, respectively). R aeruginosa AK2 was less effective in production of indole acetic acid than R fluorescens AK1. Inoculation of rice seeds with P fluorescens AK1 and P. aeruginosa AK2 showed a good level (2.30 pmol/ml and 2.1 pmol/ml) of indole acetic acid compared to uninoculated seeds (1.6 pmol/ml).