Abstract

RAPD CHARACTERIZATION OF RHIZOBIUM LEGUMINOSARUM

*Dr. S. Annapoorani and G. Buvaneswari

Abstract

Rhizobium is a gram negative aerobic, rod –shaped bacterium found in large numbers in rhizosphere of legume roots. Leguminous plants establish a symbiotic relationship with the soil bacterium Rhizobium. The Symbiosis is manifested in the formation of root nodules. Also, in the interaction of rhizobia and plants one observes a high degree of hostspecificity. Rhizobium invades roots of legumes and forms nodules on the roots. Inside the root nodules, the bacteria exist in various pleomorphic forms called bacteriods. The bacteriods fix the atmospheric nitrogen into ammonia. They provide the fixed nitrogen for plant use and draw nourishments from the root cells. Different species of Rhizobium can fix 50-200 Kg nitrogen/ha/year in leguminous crops. Hence, they have been recommendaed as nitrogen biofertilizers in agriculture. Rhizobium exhibits great degree of host. Although several species of Rhizobium live in the rhizosphere of a legume, a particular species alone can establish symbiotic association with its roots. The host specific infection of Rhizobium depends upon the specific flavonoid secreted by the roots of legumes. The root exudate induces certain genes of a particular species of Rhizobium to produce a host determinant compound on its cell wall. In most cases, the host determinant compound is a capsular polysaccharide. The development and increased availability of molecular biology techniques have made it possible to obtain information regarding the geneomic organization and diversity of rhizobia populations in different soils. Genomic DNA fingerprinting using random amplification of polymorphic DNA has been found to be useful in differentiating between very closely related bacteria, and recently this method has been used closely related bacteria, and recently this method has been for Rhizobium identification and genetic analyses. The RAPD techinique is a polymerase chain reaction (PCR) based assay that was developed to detect polymorphisms in genenomic DNA. Besides being simpler and cheaper, this method is as effective as the more labor intensive RFLP for establishing genetic relationship and identifying Rhizobium strains. The present investigation was carried out to establish genetic pattern and genetic groups of different isolates of Rhizobium leguminosarum collected from the root nodules of Arachis hypogaea using techingue of RAPD –PCR.

Keywords: Rhizobium, PCR, RAPD, RFLP, Leguminosarum, Arachis hypogaea.