An Evaluation of Auxin Hormones and ACC deaminase Production Ability by Iranian Soils Rhizobial Strains and the Effects of Superior Strains Application on Plant Growth Characteristics

It,s nowadays Proved that one can, from among many strains of rhyzobium species, find those which, in addition to high efficiency in N2 fixation, can positively affect such processes as plant growth (e.g. through production of plant growth hormones). Such strains can be useful not only to their special host, but also to other plants as well as to strategic products as grains. Soil biotechnology,one of the functions of which is to follow the production potential of biofertilizers to improve the quality of agricultural products. Proper soil fertility level and prevention of life sources contamination is highly dependent on the use of rhizobia as a good substitute for chemical fertilizers. Several researches have been performed concerning Iranian rhizobia since a decade ago in N2 fixation efficiency. So the ongoing researches were planned with the aim of evaluation of plant growth hormone as one of the abilities of PGPR group of rhizobia native to Iranian soils and evaluation of application of better inoculation on legume(alfalfa) and non legumes (wheat and corn) plants and for gaining former goal, two laboratory and green-house stages have been performed as follows: Three hundred and forteen isolates were initially selected from different rhizobial genera microscopic and biochemical tests being done on each. Fresh inoculants of each strain were prepared from stock culture, adjusted to 5* 108 cfu. mL-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 strain inoculants on growth index and alfalfa, wheat and corn yield were evaluated. The results indicated that indigenous rhizobia carry the potential of Indole auxins production (IAA and its homologues).Two hundred and ninety seven isolates (97%) from all of the isolates (314) could grow on LB-TRP medium. Among 297 isolates with the capacity of being grown on LB-TRP, 220 isolates (74.1%) could produce this hormone. The most IAA+ abundance (>90%) were seen in Sinorhizobium and the least observed in Mesorhizobium ciceri. Depending on ANOVA results, significant difference (P<0.001) has been observed in rhizobial groups and also within strains of each rhizobial group with respect to IAA production capability. The strongest rhizobial groups were Rlp, Rlv and Sm. On the other hand Rlt and Bj groups didn’t show any IAA production. Results from the application of superstrains (IAA+++) inoculants in alfalfa plant showed that IAA+++ strain had a significant increase in biological yield and N content, however, inoculation of IAA+++ rhizobial superstrain in wheat and corn didn’t show any significant increase in any of the growth features in comparison with control (treatment without fertilizer, negative control). Even a significant decrease was observed (p<0.001) in biological yield and wheat spike, dry matter; and plant height, in the case of corn.