Co-inoculation of beneficial microorganisms in upland rice cultivated at different phosphorus levels

Abstract

Beneficial microorganisms can sustainably improve rice production. This study characterized indole-acetic-acid-producing and P-solubilizing bacteria, investigating their impact on upland rice through single or co-inoculation. Four bacterial strains (BRM 063573, BRM 67205, BRM 063574, and BRM 67206) were identified by 16S rRNA gene sequencing. A greenhouse experiment was arranged in a 20 × 3 factorial design with four replications. The first factor included 18 bacterial combinations and two controls (without fertilization or inoculant, and with fertilization but no inoculant). The second factor tested three phosphorus doses (25%, 50%, and 100% of the recommended P dosage). Growth and productivity parameters were determined. Based on the 16S rRNA gene sequencing, the bacteria BRM 063574 was closely related to Stenotrophomonas maltophilia, while BRM 063573 and BRM 67206 were closely related to Bacillus pumilus and BRM 67205 was closely related to Paenibacillus pabuli. Co-inoculation treatments generally outperformed single inoculations, improving performance in number of tillers, plant height, root volume, root weight, and shoot weight. Single inoculation and co-inoculation had different effects on number of pods, number of full grain and grain weight, with co-inoculation consistently giving better results. The variability in response to single inoculation suggests an inconsistency in the performance of single inoculants. Co-inoculation, on the other hand, consistently offered advantages, improving the number of pods, number of full grains and grain weight at different phosphate doses. Based on grain production, the co-inoculants BRM 67207 + BRM 67206 and BRM 67207 + BRM 063574 are most promising for use as rice inoculants, offering consistent benefits for improving yield.