Effect of Rhizobium spp. inoculation on the polyphenol profile of common bean (Phaseolus vulgaris L.) grains

Abstract

Introduction. Symbiosis between Rhizobium spp. and common bean (Phaseolus vulgaris L.) enhances plant growth and productivity; however, its effects on grain nutritional quality have received limited attention. Objective. To evaluate the effect of inoculation with two Rhizobium spp. strains on the polyphenol content of grains from two common bean varieties, Cabécar (red) and Guaymí (black). Materials and Methods. A greenhouse experiment was conducted at CIA using autoclaved soil and five treatments: CIAT899, CR4019B, CIAT899 + CR4019B, urea, and a non-inoculated control. Plants were inoculated at sowing (10⁸ CFU mL⁻¹). Soluble and insoluble polyphenols were quantified by ultra-high-performance liquid chromatography at CIGRAS. Grain protein and saponin contents and imbibition time were also determined. Results. Inoculation significantly affected polyphenol fractions. In the Cabécar variety, CR4019B increased soluble polyphenol concentration compared with urea (p < 0.05), while inoculated treatments showed lower insoluble polyphenol levels relative to the same control. The soluble-to-insoluble polyphenol ratio was significantly higher under CR4019B, indicating that Rhizobium spp. modified the grain polyphenol profile. Conclusion. Rhizobium spp. inoculation alters the polyphenol profile of common bean grains by increasing soluble polyphenols and improving the balance between polyphenol fractions, highlighting its potential as a sustainable agronomic strategy.