Abstract:
Rice is the staple food in Sri Lanka. New improved rice varieties are cultivated for efficient
production to meet the increasing demand in Sri Lanka. However, rice yields of new
improved varieties heavily depend on synthetic fertilizer, which cause economical,
environmental and health hazards. Therefore, identification of alternative fertilization
methods is required for sustainable rice production. Use of plant associated beneficial
bacteria could be one of the best solutions to overcome these problems. Therefore, the
effect of nitrogen fixing bacterium Bradyrhizobium (ORS 278) and some locally isolated
bacteria in Sri Lankan wild, traditional and improved rice was determined for future use in
rice research. Bradyrhizobium (ORS 278) enhanced the growth and yield of Sri Lankan
rice under in vitro and greenhouse conditions. Harvest index, total chlorophyll content and
filled grain percentage significantly increased in inoculated plants. Improved rice variety
At 308 inoculated with Bradyrhizobium could grow on nitrogen free Jenson’s medium {in
vitro) while non-inoculated plants did not survive for 2 weeks. Heterosis of response to
Bradyrhizobium was evident in responsive parents and FI plants.
Forty-four bacterial isolates were collected from four species of Sri Lankan wild rice and
two weedy legumes of rice fields. All isolates were morphologically characterized and
fourteen isolates were partially identified through 16S rRNA genes sequencing.
Bradyrhizobium (ORS 278) and local isolate Bacillus megaterium have shown plant
growth promoting activities such as phosphate solubilizing ability, protease producing
ability and growth on a nitrogen free medium in vitro. These results indicate the
importance of Bradyrhizobium and other beneficial endophytic Plant Growth Promoting
Bacteria (PGPB) for future rice research particularly rice breeding.
