Abstract: To study the cross interaction of microorganisms in plant growth promotion and the effect of auxin in this interaction, Pseudomonas putida and Glomus intraradices were co-inoculated on wheat. For this purpose, a mutant that produced less amount of auxin was derived from the bacterial strain by chemical mutagenesis with ethyl methane sulfonate. Next both the wild-type strain and the mutant strain were labeled with gusA for a better detection on the roots. Finally, the bacteria were inoculated on wheat as single inoculants or combined with arbuscular mycorrhizal fungi. Controls included non-bacteria/non-arbuscular mycorrhizal fungi and arbuscular mycorrhizal fungi alone. Plants co-inoculated with the wild-type bacterial strain and Glomus intraradices had the highest stem and their fresh and dry shoot weight was more than other treatments. Also, it was observed that the wild-type strain significantly improved the mycorrhizal colonization which implies the beneficial effect of auxin on mycorrhizal colonization. Furthermore, Glomus intraradices increased the population density of the wild-type strain in the endorhizosphere. In the microscopic studies of plant roots, bacterial colonies were observed as blues lines on the surface and inside the roots as well as on the seed surfaces.