Isolation and Characterization of Indigenous Plant Growth-Promoting Rhizobacteria and Their Effects on Growth at the Early Stage of Thai Jasmine Rice (Oryza sativa L. KDML105)

Abstract

Current exploitation of rhizobacteria as plant growth regulators for application in sustainable agriculture has attracted much attention. The objective of this study was to characterize the effects of indigenous plant growth-promoting rhizobacteria (PGPR) isolated from rice rhizosphere on growth at the early stage of Thai jasmine rice (Oryza sativa L. cv. KDML105) plants. Five isolates with the ability to produce indole acetic acid (IAA) were obtained and identified by 16S rDNA sequence analysis. These strains were identified as Enterobacter sp. NRRU-N13, NRRU-N20, NRRU-N21, NRRU-D47, and Bacillus sp. NRRU-D40. In the presence of tryptophan precursor, these IAA-producing isolates produced high IAA concentrations ranging from 37.92 to 46.97 \(\upmu \hbox {g}\,\hbox { mL}^{-1}\), with the highest IAA production observed for Enterobacter sp. NRRU-N13. In addition, four of the IAA-producing isolates exhibited phosphate solubilizing activities of \(>\,400\hbox { mg}\,\hbox { L}^{-1}\), with the highest activity of \(422.50\hbox { mg}\,\hbox { L}^{-1}\) observed for Enterobacter sp. NRRU-N13. Maximum growth of rice seedlings measured in terms of root and shoot lengths and dry weights, and biomass was achieved when NRRU-N13 was employed as inoculants, thereby indicating that this isolate was the most promising PGPR. This study has highlighted the beneficial effects of PGPR isolates on growth of rice seedlings, with the isolate NRRU-N13 being the most promising one. As with the obtained results, this isolate could be used as plant growth-stimulating agents to increase crop production and yield.