A Strategic Approach for Isolation and Identification of Plant Growth Promoting Rhizobial Strains from Bhadrachalam Forest Area with Respect to Groundnut Cultivar

Objectives: To isolate and identify the crop specific Rhizobium strains for Arachis hypogaea from Bhadrachalam forest lands by an indigenous novel strategy to reduce the input cost in exploration of compatible strains for Groundnut avoiding one of the serious constrains of bio-fertilizers i.e., shelf life. Materials and Methods: Soil samples were collected randomly from 40 different locations of Bhadrachalam forest and sown with ground nut seeds in triplets. Five out of 40 samples which supported the best plant growth were taken for further investigations. The NPK and micronutrient levels of all the soil samples were found to be comparatively similar. This may be because of the fact that all the samples have been taken from same geographic region. Rhizobial strains from the ischolar_main nodules of these five samples were isolated and maintained in pure cultures. Broths of each pure culture were inoculated on the seeds sown in sterile soil and controls were maintained. Findings: The results showed that the inoculated Rhizobia tremendously improved the plant growth when compared with control. Further phylogenetic analysis revealed that the contributing organisms were Rhizobium leguminosarum, Rhizobium trifolii, Rhizobium meliloti, Rhizobium phaseoli and Bradyrhizobium japonicum. These Rhizobial species in the pure form exhibited high rate of plant growth at lab conditions followed by improved growth in low vegetative agriculture soils of the same geography. The 16S rRNA gene sequencing revealed the fact that soil sample S3 contain abundant Rhizobium leguminosarum sp., with 99% similarity. The sample 1, 2, 4 and 5 contain abundant levels of Rhizobium trifolii, Rhizobium meliloti, Rhizobium phaseoli and Bradyrhizobium japonicum and Bradyrhizobium japonicum respectively. Application: Therefore this method could be applied for the preliminary screening of compatible, species specific strains for any leguminous plants making the process easy and less expensive.