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.
