Seed inoculation with Methylobacterium symbioticum enhances growth of Phaseolus vulgaris under reduced NH4NO3 fertilization

The healthy growth of Phaseolus vulgaris relies on fertilization of nitrogen with NH4NO3. However, excessive application leads to environmental degradation, including loss of soil fertility and, green gas emissions such as N2O. As an ecological alternative, this study investigates whether reduce the dose to 50% and inoculate P. vulgaris with Methylobacterium symbioticum, an endophytic bacterium can promotes plant growth. The objective of this research was to analyze the effect of M. symbioticum on the growth of P. vulgaris plus NH4NO3 at 50%. Three isolates of M. symbioticum, obtained from P. vulgaris leaves, were individually and jointly inoculated into bean seeds. A randomized block design was used with two controls (uninoculated plants with either 100% NH₄NO₃ or water only) and four treatments (three individual isolates and one combined treatment) under 50% NH₄NO₃ fertilization. Growth performance was assessed through germination rate, plant height, root lenght, and biomass at seedling and pre-flowering stages. Data were analyzed using ANOVA and Tukey’s HSD (p < 0.05). The results showed a positive effect of M. symbioticum on the germination of P. vulgaris compared to uninoculated P. vulgaris and 100% NH4NO3. Likewise, a positive effect was observed on the phenology and biomass of P. vulgaris in the different isolates of M. symbioticum with 50% NH4NO3. There was evidence that although M. symbioticum is an endophyte of leaves of domestic plants, it can invade the root tissue of P. vulgaris. These findings suggest that inoculation with M. symbioticum allows for reduced nitrogen fertilization without compromising plant health, potentially mitigating environmental harm such as N₂O release and water contamination.