Evaluation of Inoculation of Selected Strains of Native Azotobacter chroococcum on Wheat Growth

Azotobacter is a bacterium belongs to gamma-proteobacteria class and Pseudomodaceae family with 7 species. It cannot produce spores but forms cyst. Azotobacter is able to fix molecular nitrogen non-symbiotically. It can synthesize plant growth hormones. Azotobactercan stimulate the growth of plants through different mechanisms which include nitrogen fixation, production of phytohormones such as auxins, ability of solubilizing phosphorous from the soil. In this research the soil samples from fields under cultivation of wheat in Azerbaijan-e Sharghi, Azarbayjan-e Gharbi, Kordestan, Gloestan, Fars and Khorasan provinces of Iran were collected and evaluated for isolation of Azotobacter chroococcum. The capability of auxine (Indole Acetic Acid) and hydrogen cyanide (HCN) production of selected strains was assessed. The ability of these strains for solublizing insoluble phosphates based on the ratio of corona halo to colony diameter on Sperber medium was investigated as well. The greenhouse experiment was conducted to examine the effects of inoculation of native Azotobacter in a complete factorial randomized block design on wheat growth. From 362 soil samples, 217 strains of Azotobacter isolated. One hundred two strains were selected for further investigations. The selected strains synthesized auxine (IAA) between 0-4 μgr.ml-1.24h-1. The selected strains did not show HCN production. Based on the ratio between corona halo to colony diameter in these strains the ability of solublizing insoluble phosphates was zero up to 1.3. Based on the above measurements, 37 strains were selected for greenhouse investigations. The greenhouse results showed that inoculation increased significantly the shoot dry weight and nitrogen uptake of wheat but inoculation had no noticible effects on phosphorous and potasum uptake. Based on the greenhouse results, 11 strains were selected for further investigation and field experiments.