Plant Growth Promoting Properties of a Novel Species of Rhizobium sp. Strain 11515TR Isolated from Tomato Rhizosphere in Los Baños, Laguna, Philippines

Abstract

The Rhizobium sp. strain 11515TR was established to be a novel species based on whole- genome sequencing and thus merits the evaluation of its beneficial properties to ascertain its potential as a microbial inoculant. This study was aimed at determining its growth-promoting properties and antagonistic activity, nodulation capability, and in planta growth-promoting ability. Genome and predicted proteome analysis revealed that it possesses genes for cellulases, siderophores, nodulation, NifU family protein, and a nitrogen fixation protein (ImpE). The turbidimetric assay showed that it could produce indole acetic acid. In plate assays, it was found negative for phosphate and potassium solubilization, as well as for extracellular cellulase and pectinase. It exhibited in vitro antagonistic effect against Fusarium oxysporum but not against Pseudomonas syringae, and Xanthomonas oryzae. It nodulated Centrosema pubescens, Phaseolus vulgaris, P. lunatus, and Vigna unguiculata. It did not nodulate Glycine max, Lablab purpureus, Macroptilium atropurpureum, Pisum sativum, Psophocarpus tetragonolobus, Vigna radiata, and Vigna unguiculata ssp. sesquipedalis. Under screenhouse conditions, the number and length of beans produced by Rhizobium sp. strain 11515TR-inoculated cowpea were comparable with the plants amended with commercially available Rhizobium inoculant and with chemical fertilizer. Results of this study showed that the novel Rhizobium sp. strain 11515TR has plant growth-promoting and biocontrol potentials that may contribute to its development as a possible microbial inoculant. Further work needs to be conducted to augment and confirm these results.