Diazotrophic Endophytes Symbiosis to Stimulate Growth in Rice.

Rice is one of the most important staple food crops along with wheat and maize throughout the world. Rice cultivation relies heavily on large amounts of chemical fertilizers; especially nitrogen. Manufacture of nitrogen fertilizers and their poor management in soils contribute to environmental pollution. In addition, the growth of different food crops, including rice, is now facing unprecedented challenges from global warming and climate change through climate extremes such as storms, intense rain, drought and heat waves. Plant symbionts, such as diazotrophic endophytes, have the ability to fix atmospheric nitrogen and make it available to the host plant. The use of such symbiotic partners in agriculture could provide solutions for the challenges associated with both conventional farming and climate change. Finding sustainable ways of crop production that minimize the use of nitrogen fertilizers in cultivation is a pressing need. Use of diazatrophic symbionts may be a potential strategy to mitigate undesirable consequences of climate change in agriculture. Poplar and willow diazotrophic endophytes were used to inoculate rice plants to assess their effect on host growth and development. Rice var. M206 was used in the greenhouse and laboratory studies. Six poplar and three willow endophyte species were used as a consortium for the greenhouse studies. Three poplar endophyte species labeled with green fluorescent protein were used to verify the colonization in the laboratory experiments. Inoculated rice plants in the green house showed significantly higher biomass and tiller numbers per plant as compared to mock-inoculated plants. These endophytes effectively colonized rice plants; and were observed mainly in young lateral roots. They colonized primarily intercellular spaces between cells but Rhizobium tropici was observed in both intercellular spaces and vascular tissues. The use of endophytes labeled with green fluorescent protein is an effective way to visualize the endophytes’ community in the plant interior.