This investigation was carried out to evaluate Indole acetic acid (IAA) production by isolated bacteria from drought and salinity affected soils. Four hundred bacteria were isolated from soils with different levels of electrical conductivity (EC) and sodium adsorption ratio (SAR). Then the ability of these bacteria to produce IAA and the effects of different amounts of tryptophan and drought-salinity tensions on IAA production were analyzed. Results indicated that the effects of drought and

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... nity tensions on variability of IAA production were statistically significant. One of the bacterial species isolated from saline-sodic soils, Arthrobacter siccitolerans, was IAA producer and data comparison indicated that under drought stress conditions it produced IAA 84.3% higher than isolate RS11. While isolated RS11 produced highest rate of IAA (10.42 µg.ml -1 ) under normal conditions. Also, A.siccitolerans continued to produce IAA until the EC was 40 dS.m -1 and OP (Osmosis pressure) was -20 bar. The amount of IAA production per unit of applied tryptophan in this bacterium was 0.1 and in others it was lesser. According to experiments, the relative preference of this bacterium was verified and proposed for field experiments in drought, salinity and salinity-sodicity affected soils. Keywords . drought, electrical conductivity, IAA, sodium adsorption ratio 186/186 ‫سلیماوی‬ ‫ي‬ ‫همکاران‬ . ‫ي‬ ‫شًری‬ ‫ي‬ ‫خشکی‬ ‫های‬ ‫تىش‬ IAA Soleiman et al. The drought and salinity and IAA