Physiological Characterization and Genetic Diversity Assessment of the Rhizobial Populations Inhabiting Gliricidia sepium in selected Locations of Ampara District, Sri Lanka

Abstract

Purpose: Gliricidia sepium is a wide spread multipurpose legume plant which is effective in nitrogen fixation and host to many Rhizobial strains. However, few studies have been carried out to identify and characterize the Rhizobial populations inhabiting G. sepium in Sri Lanka. The main objective of this study was to isolate and identify the stress tolerant Rhizobial strains in G. sepium. Research Method: Root nodules of G. sepium were collected from seven locations in Ampara district, which belongs to dry zone in Sri Lanka. Total of 35 isolates were screened for the tolerance for different pH, salinity, drought conditions and temperatures separately as well as in combinations. Genetic diversity of stress tolerant isolates was assessed using ERIC fingerprinting. Findings: All isolates were grown under wide range of stress conditions. The Rhizobial strains isolated from the site closer to the coast showed a high tolerance for all salinity levels as they are adapted to the high salt stress experienced in their natural habitat. The growth response to drought conditions and temperature was variable. Moreover, 14 isolates showed a high tolerance for more than two extreme stress conditions. When extreme conditions were combined, 12 isolates among 14 were survived. These 14 isolates grouped in to ten clusters at 69% similarity coefficient that make them genetically diverse. Research Limitation: The stress tolerance was observed under laboratory conditions and it does not provide enough evidence for the effectiveness of selected isolates in field. Original Value: The 14 stress tolerant Rhizobial isolates can be used to cross inoculate crop legumes to identify possible cross inoculation groups in order to reduce nitrogen fertilizer usage.