Evaluation of Plant Growth Hormones Production (IAA) Ability by Iranian Soils Rhizobial Strains and Effects of Superior Strains Application on Wheat Growth Indexes

Proving of rhizobia’s other abilities in spite of Nitrogen fixation ability and considering these bacteria as plant growth promoting rhizobacteria (PGPR), researching tasks in this field have increased. Now, it’s completely proved that we can find such strains among many more strains of each rhizobial group that can also do effective process in plant growth promoting as plant growth hormones production, in addition of their ability in N fixation. Such strains can be useful not only for their special host, but also for other plants. 2 At first, 100 isolates selected from different rhizobial genus and microscopic and biochemical tests were done on each of them. Fresh inoculants of each strain were prepared from stock media, adjusted to 2.4*10 cfu.ml 9 1 and isolates evaluated on their potential production of auxin hormone (IAA and its homologues) by Brick (1991) on LB solid medium which was improved with TRP. Application effect of IAA super strains inoculants on + wheat growth indexes were evaluated. The results were indicated that indigenous rhizobia have the potential of Indole auxins production (IAA). Depend on ANOVA results, significant difference (P<0.001) has been observed in rhizobial groups and also in the strains of each rhizobial group from the point of IAA production capability. Greenhouse test results on wheat showed that bacterial treatment and also the Ag and Trp. Treatments had significant effect on measured parameters. Comparison of means shows that there is a significant difference between the rhizobial treatment effects on the measured parameters too. Also the mean comparison of Ag and Trp. Treatments shows that usage of both Ag and TrpTreatments together cause a significant increase on measured parameters in comparison with using Ag and Trp Alone and also in comparison with the blank. So, the most important promotion mechanism b yrhizobial strains, is production of Indole phytohormones (IAA) which results the better root growth, so increase of water and micronutrient (N, P and K) uptake by the plant and increase of the plant growth.