Advantages And Disadvantages Of Rhizobacteria

By the year 2050 the world’s population will reach 9.1 million. In order to feed this larger population food production must increase. And it demands high crop yield to provide food for all. For this purpose the use of chemical fertilizers and pesticides has been very high. Though satisfactory crop yield is obtained by the application of chemical fertilizers and pesticides, their use brings out certain disadvantages. These include pollution of large water resources, destruction of microorganisms, acidity of the soil and reduction in soil fertility etc. In recent years scientists have found an alternative way to deal with this deleterious effect of chemical pesticides. Currently, there is a great interest in the field of bacterial interactions
Microorganisms inhabiting rhizospheres of plants are called Plant growth-promoting rhizobacteria (PGPR).They are free living ,soil borne ,root-colonizing bacteria that form symbiotic relationships with many plants .They can be classified into extracellular plant growth promoting rhizobacteria (ePGPR) and intracellular plant growth promoting rhizobacteria (iPGPR) . The ePGPRs may exist in the rhizosphere, on the rhizoplane or in the spaces between the cells of root cortex while iPGPRs locates generally inside the specialized nodular structures of root cells. The bacterial genera such as Agrobacterium, Arthrobacter, Azotobacter, Azospirillum, , Bacillus,Burkholderia,Caulobacter,Chromobacterium,Erwinia,Flavobacterium,Micrococcous,Pseudomonas and Serrata belongs to ePGPR.The iPGPR belongs to the family of Rhizobiaceae includes Allorhizobium,Bradyrhizobium,Mesorhizobium and Rhizobium.Plant growth promoting rhizobacteria promote plant growth either directly or indirectly. In direct method due to their ability for nutrient supply (nitrogen, phosphorus, potassium 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, root colonizers, and environmental protectors
Up to 80% of rhizobacteria can synthesize indole-3-acetic acid(Loper and Schroth, 1986).Beneficial Azospirillum sp., Alcaligenes faecalis,Klebsiella, Enterobacter cloacae, Acerobacter diazotrophicus, Pseudomonas and Xanthomonas,Herbaspirillurn seropedicae , symbiotic Rhizobium, and Bradyrhizobiurn do produce IAA in the culture medium. It is of interest to study IAA production by bacteria, not only because of the physiological effect that this phytohormone causes on plants, but also in view of the possible role in plantbacteria interactions (e.g., Rhizobium symbiosis). Most commonly, IAA producing PGPR strains are believed to increase root growth and length resulting in greater root surface area which enables plants to access more nutrients from soil (Gupta et al., 2002). Pattern and Glick (2002) demonstrated that bacterial IAA from P. putida played a major role in the development of host plant root system. Plant host also like to depend on its rhizobacterial flora for IAA instead of wasting the metabolic energy for the synthesis of IAA.This is because the rhizobacteria maintain positive interactions with the host plant by supplying IAA and stimulating its growth; in return they utilize plant root exudates as a source of carbon and