biofertilizers containing plant growth promoting rhizobacteria: strengths and weaknesses

to date there is not progress commercially production and large scale application of pgpr in agriculture. one reason for limited commercial use of pgpr is variability, inconsistency and irreproduciblility of results between laboratory, greenhouse, and field trials. these problems with pgpr arises from variation in crops and cultivars, the physical, chemical and biological composition of  soils, the content of soil organic matter, competition of indigenous microorganisms, soil moisture content, climate, or perhaps an incomplete understanding of the other mechanisms of pgpr that can affect on plants growth. therefore, it is difficult to evaluate recommendable numbers of microorganisms in pgpr inocula and the appropriate time, place and application methods. on the other hand, low cost of chemical fertilizers in iran has precluded any serious consideration to the extension of pgpr application in iran. the documented reports of pgpr application in iran indicated that more trials are conducted in invitro, greenhouse and out of farm. being decentralized research, low content of soil organic matter, the problems with industrial commercialization, being non-targeted chemical fertilizer subsidies, indecisiveness and uncertainty to ensure effectiveness of pgpr in all times and places, lack of inappropriate communication between the research sector, production and extension and the absence of proper mechanisms for supervision and quality control of commercial inoculants are some of the most important challenges with pgpr application in iran. in other hand there are strengths, because there are many students that interested in studying trends in soil biology and there are many training center for this students in iran. however, because of national archives including fifth development plan and 20-year outlook there is a clear vision about development of biofertilizers in iran.