Currently there is much interest in soil bacteria of the genus Azospirillum, which lives in association with important crops such as cereals. These bacteria is now used as a biofertilizer for its potential to fix dinitrogen and to produce plant growth hormones. To determine the occurrence and activity of this bacteria in some soils of IRAN, 52 root and rhizospheric soil samples of maize, wheat and some grasses were collected from four provinces(Tehran, Semnan, Fars and Qhazvin). Isolation of bacteria was carried out by selective media. Genus and species identification was performed based on microscopic examinations, acetylene reduction assay and biochemical tests. Twenty three strains were isolated and identified as Azospirillum and 10 strains that showed better growth and nitrogenase activity were selected for inoculation.In a greenhouse experiment,corn (single cross hybrid 704) and wheat (falat variety) seeds were germinated in sterile conditions and in time of planting,seedlings were inoculated with three foreign and 10 selected native strains of Azospirillum.Results obtained in this study showed that inoculation with Azospirillum mostly increased the height, shoot and root dry matter and root to shoot dry matter ratio of wheat and maize plants compared with control (uninoculated).Inoculation with Azospirillum, also enhanced the root branching and generally improved the root system. Most of the native strains had batter effects on different growth indices of inoculated plants (height, root and shoot dry matter) than foreign strains.
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