World Applied Sciences Journal 6 (11): 1576-1584, 2009 ISSN 1818-4952 © IDOSI Publications, 2009 Corresponding Author: H. Etesami, Department of Soil Science, Tehran University, Iran 1576 Evaluation of Plant Growth Hormones Production (IAA) Ability by Iranian Soils Rhizobial Strains and Effects of Superior Strains Application on Wheat Growth Indexes Hassan Etesami, Hossein Ali Alikhani and Abolfazl Ali Akbari 1 1 2 Department of Soil Science, Tehran University, Iran MSc. in Irrigation and Drainage, Firozabad Azad University Abstract: 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. Key words: Rhizobacteria PGPR Plant Growth Hormone (IAA) Wheat INTRODUCTION lastly, promotion of ethylene production subsequently Rhizobia the Production Ability of Pant Growth is the common natural auxin that shows all auxin doing Promoting Auxins: Rhizobial bacteria are the best actions and extensively affects pants physiology[4]. plant growth promoting among rhizobactia. The bacteria Triptophan (L-trp) is physiologically a precursor of auxin increase plant growth and yield by various methods. biosynthesis in higher plants and microorganism [5, 6]. Some PGPR strains, for example, able to enhance the The root exudates are the main resource of Trp in soil. growth and development of plants by interfering in the Kravchenko et al. (1994) measured and reported that trp concentration of known phytohormones [1, 2]. Among concentration in tested grain root exudates was about 8.3 plant hormones, auxins and ethylene play an important to 390 ng seedling a day [7]. Various reports show Trp- role in root system development and lastly, plants yield derived microbial auxins present in the rhizosphere area [3]. Among phytohormone, auxin is the first hormone play a very important role in growth and development of identified by Darwin in 1880. The hormone name has plant rooting system and crop yield [8, 9, 10].Including derived from the term auxein namely increasing. Auxins Sarwer and Frankenberger (1994) surveyed the effect of play an important role in Elongation of plant cells, tropism, Trp compared with Indole-3-acetic acid on the maize plant apical dominance, root formation and root elongation and growth in a greenhouse study. Obtained results showed evolution and ripening fruits. Indole -3-acetic acid (IAA)