Isolation of abiotic stress tolerant rhizobia inhabiting Mucuna bracteata from selected locations of Puttalam district, Sri Lanka
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Date
2024-11-01
Authors
Chandraratne, G. W. I. U.
Samarakoon, S. M. N. S.
Rajapakse, R. G. S. C.
Journal Title
Journal ISSN
Volume Title
Publisher
Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka
Abstract
The symbiotic relationship between legumes and Rhizobium significantly aids in the growth and development of crops by promoting biological nitrogen fixation in nitrogen-depleted soil. Rhizobium is a group of soil bacteria that form mutualistic relationships with leguminous plants like Mucuna bracteata, which exhibit high nitrogen fixation ability. However, only a few studies have focused on the identification of stress-tolerant rhizobial populations inhabiting M. bracteata. A total of 35 rhizobial strains that are resilience to environmental stresses were isolated from the root nodules of M. bracteata from seven locations (Madampe, Dankotuwa, Wijayakatupotha, Pallama, Puttalam, Kumarakattuwa, and Bangadeniya) in Puttalam District, Sri Lanka. The isolated rhizobial strains were subjected to different physiological conditions such as temperature (25 °C-45 °C), drought (polyethylene glycol 8000 concentrations, 0.1% - 0.4%), pH (3.0 - 9.0), and salinity (NaCl concentrations, 0.1% - 3.0%). Stress-tolerant rhizobial strains were selected based on statistical analysis of spectrophotometric absorbance measurements. Due to high salinity levels in seven sites, rhizobial strains showed a high growth at 1% salt concentration and less tolerance with increasing salt concentrations. The rhizobial strains showed optimal growth at 35 °C because the Puttalam district temperature varies from 20 °C to 36 °C. Except for Pallama and Kumarakattuwa sites, most of the rhizobial strains showed high absorbance under varied drought conditions. Rhizobium growth was hindered at pH 3.0 and 4.0 but it increased up to pH 7.0 because of the optimum growth of rhizobia at soil pH 6.0 - 7.0. Among these isolates, 16 isolates exhibited tolerance to more than two physiological conditions, with nine isolates identified as the best tolerant rhizobial strains. These most tolerant strains can be cross-inoculated with crop legumes to remedy the widespread use of chemical nitrogen fertilizers.
Description
Keywords
Biological nitrogen fixation , Rhizobium , Stress tolerance
Citation
Proceedings of the Postgraduate Institute of Science Research Congress (RESCON) -2024, University of Peradeniya, P 141