عنوان مقاله [English]
نویسنده [English]چکیده [English]
Azotobacter is a gram negative, aerobe, chemo-organotroph with the, polymorphism including rod, cocci and ovoid forms. This bacterium belongs to gama-proteobacteria class, Pseudomonaceae family with 7 species. It cannot produce spores but forms cyst. Azotobacters’species lives in different regions from tropicals to poplars in pH 3-9. However, it can be fined mainly in alkaline and natural soils. Azotobacter is able to fix non-symbiotically molecular nitrogen. It can synthesize aminoacids, plant growth hormones, vitamins, and exo-polysaccharides. The population of Azotobacter in soils is lower than 104 cells per gram of soil. The number of Azotobacter in some soils of Iran is about 1.5×103. Azotobacter affect the plant growth by nitrogen fixation, producing plant growth promoting hormones, solubilizing inorganic phosphates, increasing nutrients uptake, increasing resistance to stress conditions and biocontrol of plant pathogen agents. Some species of Azotobacter are able to remediate some contaminants. There are many reports about significant effects of Azotobacter inoculation on different plants e.g. cereals, vegetables and fruit trees. There are some constraints on the extension of traditional production of Azotobacter inoculants such as low organic matter in many soils, uncertainty in reproducibility and effectiveness and lack of competitiveness with chemical fertilizers for yield increasing. However, long life of Azotobacter in soils and inoculum packages and ability to use for many ranges of plants are the most important of its comparative advantages. Accumulation of plant growth stimulating characteristics in certain strain and creating the ability of symbiotic relation with plants e.g. cereals by molecular studies is recommended for future investigations.
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