According to Kloepper and Schroth (1981), PGPR mediated plant growth promotion occurs by the alteration of the whole microbial community in rhizosphere niche through the production of various substances (Table 2) (Kloepper and Schroth, 1981). Generally, PGPR promote plant growth directly by either facilitating resource acquisition (nitrogen,
phosphorus and essential minerals) or modulating plant hormone levels, or indirectly by decreasing the inhibitory effects of various pathogens on plant growth and development in
the forms of biocontrol agents