**2.6 Microbiological control of pathogens**

In modern agriculture, biological control of pathogens using microorganism is playing a major role in disease control of crops. Beneficial microorganisms are used as biopesticides and is known to be the most effective methods for safe cropmanagement practices [74].

The rhizosphere was discovered by Hiltner [75] to be the layer of soil dominated by the root, and is much richer in bacteria than the surrounding bulk soil. The plant rhizosphere is regulated by the synergistic relationship between the soil, plant root, and the microbes present and is controlled by the soil pH, texture, complexity and plant roots exudates mainly composed of sugars, amino acids and various nutrients [27]. The rhizosphere is a zone of soil that surrounds the plant root, is a niche colonized by numerous organisms and is considered as one of the most complex ecosystem on Earth [76].

There are some heterogeneous group of bacteria known as Plant growthpromoting rhizobacteria (PGPR), they are free-living soil bacteria mostly found in the rhizosphere, at the rhizoplane or in association with roots. They are used as biocontrol agent for the control of plant pests and disease by suppressing the activity and growth of phytopathogenic organisms, and also help to improve the extent or quality of plant growth directly or indirectly [77] by providing nutrients, synthesizing phytohormones, solubilizing phosphate, reducing stress, alleviating soil contamination with heavy metals [78–83] or improving the microbial community structure of the rhizosphere [84, 85]. The following genera of bacteria have been reported as PGPR: *Agrobacterium*, *Arthrobacter*, *Azoarcus*, *Azotobacter*, *Azospirillum*, *Bacillus*, *Burkholderia*, *Caulobacter*, *Chromobacterium*, *Enterobacter*, *Erwinia*, *Flavobacterium*, *Klebsiella*, *Micrococcous*, *Rhizobium*, *Pantoea*, *Pseudomonas* and *Serratia* [86, 87] which have shown prospect as biocontrol agents against various fungal pathogens [87].
