Phosphate solubilizing bacteria belong to the PGPR [17]. PGPR exert their beneficial effect on plant growth by different
mechanisms of action, having a direct effect like the production of phytohormones and cytokinins or by improving plant
nutrition, or by indirect mechanisms which improve plant health, like biological control of pathogens or the induction of
systemic resistance in plants which can be compared to the improvement of the immune system in animals. Some PGPR can
stimulate the symbiosis between plants and AM fungi.