**11. Compatibility between** *Rhizobium* **and PGPR**

Under natural soil conditions microorganisms are effective to colonize the plant roots for function. Compatibility between the PGPR and other microorganism to

*Characterization of* Rhizobium *and Plant Growth Promoting Rhizobacteria from French Bean… DOI: http://dx.doi.org/10.5772/intechopen.100592*

colonize the root system without inhibiting each other is a prerequisite for getting beneficial result using multiple microbes in a crop field. The use of mixed cultures of beneficial microorganisms as soil inoculants is based on the principles of natural ecosystems which are sustained by their constituents such as the quality and quantity of their inhabitants and specific ecological parameters [99]. In the rhizosphere, PGPR and nodule promoting rhizobacteria induce phytoalexins production by the plant, creating antibiosis in the rhizosphere for pathogenic forms, siderophores production to chelate insoluble cations and associative action with the plant [100, 101]. *Rhizobium* as a gram -ve bacteria, is able to establish symbiosis with leguminous plants such as *Cicer* as well as many other rhizobacterial strains, and develops positive interactions with legumes by inhabiting root nodules. Within these nodules, bacteria reduce atmospheric nitrogen to ammonia which acts as a sufficient useable nitrogen source [102]. Studies on legume rhizosphere bacteria have shown that besides indigenous rhizobia interacting and competing for nodulation with an inoculant strain by antagonistic or synergistic interactions, other diazotrophs such as *Azotobacter* and *Azospirillum* as well as rhizosphere fungi and bacteria especially species of *Pseudomonas* and *Bacillus* do interact with *Rhizobium* affecting nodulation and nitrogen fixation [58].

## **12. Impact of PGPR on French bean**

The effect of Plant growth promoting rhizobacteria on plant growth is a well-documented fact. PGPR plays an important role in agricultural systems, especially as biofertilizer. A positive influence of inoculation with various PGPR isolates on shoots and roots length; dry biomass production; and shoot: root ratio was studied by Yadav [69]. The higher shoot length, root length, root volume and dry biomass production due to inoculation with various PGPR isolates could be attributed to their plant growth promoting traits such as IAA, GA, P-Solubilization, Zn-Solubilization, ammonia production, HCN production and nitrogen fixation. IAA and GA are the plant growth hormones in which IAA controls processes *viz*; differentiation, division and enlargement of cells which controls plant growth whereas GA plays pivotal role in growth and development of plants. In most of the observed studies, the growth controller especially IAA, influences most of the root system like primary root growth, side root and piliferous layer formation [103] helps in plant growth promotion. The significant increase in growth of shoot and root due to inoculation of isolates indicates that the bacterial isolates have ability to provide better nutrient flux to the plant host which resulted in the increase of the plant biomass and N accumulation. Beneficial responses of PGPR due to beneficial interaction with rhizobia on legumes have been reported by various workers [75]. An increase in shoot: root ratio of French bean due to inoculation with the PGPRs isolates indicated that carbohydrate might be translocated to shoot but increase in root: shoot ratio in plant due to inoculation with isolates indicated more accumulation of carbohydrates in root rather than its portioning. High root: shoot ratio of plant indicated that plant may be survived in water or salinity stress conditions. The high root: shoot ratio due to inoculation of PGPR was also reported by [69]. Kloepper [42] reported that various PGPR isolates can alter the root architecture and promote plant development through the synthesis of different phytohormones such as IAA, GA and cytokinin. Stefan et al. [104] studied the effects of inoculation with PGPR on photosynthesis, antioxidant status and yield of runner bean and reported that PGPR strains used for seed inoculation induced significant increase in photosynthetic rate at 20 DAI. Increased photosynthetic activity is a consequence of a higher N incorporation which contributed to the formation of chlorophyll [105].

Inoculation of PGPR strains increased the nutritive value of grains by increasing the soluble protein content up to 16.24 per cent and total reducing carbohydrates concentration up to 49.28 per cent.
