Diversity of pseudomonads isolated from three different plant rhizospheres

Aims: To study the diversity of the Pseudomonas populations isolated from t hree different plant rhizospheres, namely pearl millet, cotton and paddy, g rown in saline soils along the coastline of Southern India. Methods and Results: The Pseudomonas populations were analysed for their bi ochemical characters and genetic diversity using molecular tools including RAPD and PCR-RFLP. The biochemical characterization, antibiotic resistance assay and RAPD profiles revealed a largely homogenous population. Even in P CR-RFLP restriction studies, only two groups of isolates were seen. One gro up was predominant in all three rhizospheres, while the other minor group c onsisted of salt-sensitive isolates restricted to the paddy rhizosphere alo ne. Conclusions: It was observed that increasing salinity caused a predominant selection of salt-tolerant species, in particular Ps. pseudoalcaligenes and Ps. alcaligenes irrespective of the host rhizosphere. Significance and Impact of the Study: This study has reinstated the importa nce of the soil over the host plant with regard to rhizosphere populations. It has also resulted in the isolation of several salt-tolerant Pseudomonas strains, which are being screened for their biological control activity ag ainst common plant pathogens of the coastal agri-ecosystem.