Interactions of rice seedlings with bacteria isolated from rice roots

Abstract

The interactions between two groups of rice endophytic bacterial strains and several rice cultivars were investigated. Various strains of Rhizobium leguminosarum bv. trifolii, originally isolated from rice plants grown in Egypt, comprise one group. The second group of bacterial strains was isolated from rice cultivars grown in the Philippines. Inoculation experiments with rice seedlings showed that specific isolates of these rice-associating bacteria could either promote, inhibit, or have no influence on rice plant growth. Furthermore, these growth effects were greatly influenced by the environmental growth conditions used. Studies to examine root colonisation patterns, using Rhizobium strains into which a plasmid expressing the green fluorescent protein has been placed, showed that the bacteria preferentially colonise rice seedling surfaces mainly in clumps. This occurs along grooves on the rice root surface, or at the emerging lateral root zones and at the root tips. However, rhizobia could also colonise intercellularly in lateral roots formed on the main roots near the culm region of the seedling. Under the growth conditions used, this occurred most frequently with strain R4 which multiplied and migrated to form long lines of individual bacterial cells along the inside of growing lateral roots. A bioassay to measure bacterial multiplication in rice leaves showed that the rice-associating strains can multiply and survive at different rates within these tissues. They were not, however, detected migrating into other parts of the leaf from the original site of pressure-infiltration, indicating that the bacterial ability to migrate within the lateral roots is not matched by a similar capacity in rice leaves. We suggest that some of these rice-associating bacteria possess important genes that enhance their ability to intimately colonise niches on and within rice tissues, and promote rice plant growth.

Diversity of native rhizobia isolated in south Brazil and their growth promotion effect on white clover (Trifolium repens) and rice (Oryza sativa) plants

“…Rice is one of the most important cereals in the world and the main dietary component of 20 % of the world's population (IRRI and AfricaRice 2010; Seck et al 2012). Rhizobia strains that belong to different genera are able to establish endophytic relationships with rice plants (Prayitno et al 1999;Biswas et al 2000a, b;Peng et al 2002) and to promote shoot growth and enhance grain production (Mia and Shamsuddin 2010;Costa et al 2013). Cho et al (2003) reported that white clover cultivated prior to rice in a notillage system produced nearly sufficient levels of N for rice cultivation and only other deficient minerals needed to be applied.…”

Ascending Migration of Endophytic Rhizobia, from Roots to Leaves, inside Rice Plants and Assessment of Benefits to Rice Growth Physiology

“…Among these, Rhizobium is most thoroughly studied because of its ability to induce root nodules on legume plants of agricultural importance and provide these plant hosts with fixed nitrogen, enabling them to grow productively in nitrogen-limited agricultural soils (12,21,34,36). Recent studies indicate that Rhizobium also endophytically colonizes roots of certain cereal crop plants, promoting their growth and grain yield at harvest while reducing their dependence on chemical fertilizer inputs, independent of root nodulation and biological N 2 fixation (2,3,5,15,17,22,23,26,27,37,38). For instance, the beneficial growth responses of rice to rhizobia include increased seed germination, rate of radical elongation, seedling vigor, root architecture (length, branching, biovolume, surface area), shoot growth, photosynthetic activity, stomatal conductance, shoot and grain N content, harvest index, agronomic N fertilizer use efficiency, and grain yield.…”

Are common symbiosis genes required for endophytic rice-rhizobial interactions?

“…4,7 Despite being unable to induce nodulation, rhizobia have been shown to be able to infect and colonize the roots of nonlegumes such as rice (Oryza sativa). [8][9][10] This so-called "endophytic" interaction also can promote plant growth, even though the exact mechanisms for such positive responses are not well understood.…”

“…4,7 Despite being unable to induce nodulation, rhizobia have been shown to be able to infect and colonize the roots of nonlegumes such as rice (Oryza sativa). [8][9][10] This so-called "endophytic" interaction also can promote plant growth, even though the exact mechanisms for such positive responses are not well understood. 9,11 Characterization of the infection and colonization processes of the rice-rhizobial association revealed that the bacteria primarily enter the plant tissue through root hairs and/ or crack entry located near the sites of newly emerging lateral roots.…”

“…4,7 Despite being unable to induce nodulation, rhizobia have been shown to be able to infect and colonize the roots of nonlegumes such as rice (Oryza sativa). [8][9][10] This so-called "endophytic" interaction also can promote plant growth, even though the exact mechanisms for such positive responses are not well understood.9,11 Characterization of the infection and colonization processes of the rice-rhizobial association revealed that the bacteria primarily enter the plant tissue through root hairs and/ or crack entry located near the sites of newly emerging lateral roots.10 Similar infection strategies are also used by the rhizobia to enter the roots of the non-legume Paraponia and the water-tolerant legume Sesbania rostrata, both of which can nodulate with rhizobia.12-16 Intriguingly, similar to what occur in legumes, both root hair curling and infection thread-like structures were also Legume plants are able to establish root nodule symbioses with nitrogen-fixing bacteria, called rhizobia. recent studies revealed that the root nodule symbiosis has co-opted the signaling pathway that mediates the ancestral mycorrhizal symbiosis that occurs in most land plants.…”