OVERVIEW OF PGPR (PLANT GROWTH PROMOTING RHIZOBACTERIA)
Keywords:
PGPR, Nitrogen fixation, Phytohormone, Phytopathogen, RhizosphereAbstract
Nowaday, microorganisms play the important role in agricultural system, especially the group of bacteria called plant growth promoting rhizobacteria (PGPR). PGPR are widely studied because of their potential for plant production under three characteristics. Firstly, PGPR act as biofertilizers provide nitrogen via nitrogen fixation reaction, which can subsequently be used by the plants. Secondly, phytostimulators can directly promote the growth of plant, usually by the production of hormones. Finally, as biocontrol agents are able to protect plant from phyto-pathogenic organisms. PGPR can be separated into 2 types based upon their localization; extracellular PGPR (ePGPR), existing in the rhizosphere and intracellular PGPR (iPGPR), which exist inside root cells. For the binding of bacteria to the plant, organic chemical such as N-acetyl-homoserine lactone are secreted by a wide variety of bacteria as a signaling. They can induce and enhance genes which involve in adhesion. This system is called quorum sensing. Thereafter bacteria are attached to the plant root, this mechanism is somewhat similar to biofilm production in the environment. Then the interaction between two partners is started. On the other hand, the defense mechanism from plant to PGPR are to produce ethylene, jasmonic acid (JA) and salicylic acid (SA) via the plant systemic acquired of resistance (SAR). The application of PGPRs in agricultural system as inoculants are being very attractive as it would substantially reduce the use of chemical fertilizers and pesticides. A growing number of PGPR are being marketed in the developed countries such as EU and USA.
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