Photosynthetic Bradyrhizobia Are Natural Endophytes of the African Wild Rice Oryza breviligulata

Abstract

We investigated the presence of endophytic rhizobia within the roots of the wetland wild rice Oryza breviligulata, which is the ancestor of the African cultivated rice Oryza glaberrima. This primitive rice species grows in the same wetland sites as Aeschynomene sensitiva, an aquatic stem-nodulated legume associated with photosynthetic strains of Bradyrhizobium. Twenty endophytic and aquatic isolates were obtained at three different sites in West Africa (Senegal and Guinea) from nodal roots of O. breviligulata and surrounding water by using A. sensitiva as a trap legume. Most endophytic and aquatic isolates were photosynthetic and belonged to the same phylogenetic Bradyrhizobium/Blastobacter subgroup as the typical photosynthetic Bradyrhizobium strains previously isolated from Aeschynomene stem nodules. Nitrogen-fixing activity, measured by acetylene reduction, was detected in rice plants inoculated with endophytic isolates. A 20% increase in the shoot growth and grain yield of O. breviligulata grown in a greenhouse was also observed upon inoculation with one endophytic strain and one Aeschynomene photosynthetic strain. The photosynthetic Bradyrhizobium sp. strain ORS278 extensively colonized the root surface, followed by intercellular, and rarely intracellular, bacterial invasion of the rice roots, which was determined with a lacZ-tagged mutant of ORS278. The discovery that photosynthetic Bradyrhizobium strains, which are usually known to induce nitrogen-fixing nodules on stems of the legume Aeschynomene, are also natural true endophytes of the primitive rice O. breviligulata could significantly enhance cultivated rice production.

Expressed nifH Genes of Endophytic Bacteria Detected in Field-Grown Sweet Potatoes (Ipomoea batatas L.)

“…and A. caulinodans also infect plants through cracks at the base of the root primordia, not only in the roots but also in the stems of leguminous plants. They are also known to enter the roots of non-leguminous plants such as rice and wheat via cracks 6,27,38) . In the present study, nifH sequences homologous to Bradyrhizo- Clones that exceeded 99% base sequence similarity with each other were divided into different groups and a representative clone was chosen from each group.…”

Epidemic Spread of Symbiotic and Non-Symbiotic Bradyrhizobium Genotypes Across California

“…Bradyrhizobium is the most cosmopolitan rhizobial lineage and is found free-living in soils and in aquatic environments as well as in symbiotic association with plant and animal hosts, including humans [29][30][31][32][33][34][35][36][37]. Recent work suggests that there are~19 species of Bradyrhizobium that form symbiotic associations with legumes [36], although non-symbiotic strains are also common in soils [37].…”

Isolation, Identification, Biochemical and Antibiotic Sensitivity Characterization of Rhizobium Strains from Vigna mungo (L) Hepper, Cicer arietinum L and Vigna radiata (L) R Wilczek in Muzaffarnagar, Uttar Pradesh, India

“…There are several different genera of Rhizobia, all of them belong to the Rhizobiales, a probably-monophyletic group of protobacteria and they are soil bacteria characterized by their unique ability to infect root hairs of legumes and induce effective N 2 -fixing nodules to form on the roots. Unlike many other soil microorganisms, Rhizobia produce no spores and they are rod shaped, aerobic and motile (Chaintreuil et al, 2000). Inoculation plants and spoil with Rhizobium can improved soil fertility and reduce the production cost of next crop through reduced input in the form of nitrogen fertilizers and which also minimize hazard effects of fertilizers on human, soil and environmental health (Mia and Shamsudin, 2010).…”