Endophytic rhizobia promote the growth of Cuban rice cultivar

Bacteria from the rhizobia group have been previously identified as grass-endophytes in grassland with cropping history of legumes. In this paper we aimed to demonstrate that strains of the Rhizobium genus, isolated from the rhizosphere of a rice Cuban cultivar subjected to intensive monoculture management, behave as endophytes and promote its growth. Eleven bacteria previously isolated from the rhizosphere of rice plants, were screened for their plant growth promoting traits. We found that some of them were able to solubilize inorganic phosphate compounds, produce siderophores and biofilm, have exocellulase and protease activity and were able to inhibit the phytopathogen Pyricularia oryzae growth. The phylogenetic analysis using partial sequences of 16S rRNA gene showed that bacteria isolated from rice plant of cultivar INCA LP-5 belonged to Rhizobium, Agrobacterium and Pseudomonas genera. Two strains analyzed, Rhizobium sp. Rpr2 and Rdp16, increased the height and biomass of rice plants, 70 days post-inoculation in greenhouse conditions. According to the quantification of Rhizobium sp. strain Rpd16 in surface-disinfected tissues of root and sheath, together with the analysis of confocal microscopy images, we can conclude that the Rdp16 strain is a rice endophyte of the cultivar INCA LP-5. This investigation is the first evidence of endophytic rhizobia able to promote the rice growth of a Cuban cultivar subjected to intensive monoculture, without rotation with legume plants and without a previous history of rhizobia inoculation.

Automated summary

This study found that bacteria from the Rhizobium genus isolated from the rhizosphere of a Cuban rice cultivar acted as endophytes and promoted rice growth. These bacteria exhibited various plant growth promoting traits, such as phosphate solubilization, siderophore and biofilm production, cellulase and protease activity, and inhibition of phytopathogen growth. Additionally, two strains of Rhizobium increased rice plant height and biomass in greenhouse conditions.