Bacterial consortia among Bradyrhizobium species, Azospirillum baldaniorum and Bacillus pumilus promote plant growth and efficient symbiotic nitrogen fixation in mung bean

Abstract

The use of nitrogen-fixing bacteria in leguminous plants is a widespread approach, and the exploration of symbiotic bacteria that are efficient in biological nitrogen fixation (BNF) continues to be explored. The aim of the present study was to evaluate the effect of inoculation and coinoculation of mung bean plants with different combinations of Bradyrhizobium (B. elkanii BR 2003, B. pachyrhizi BR 3262, B. yuanmingense BR 3267, B. paxllaeri BR 10398 and B. icense BR 10399), Azospirillum baldaniorum (Sp245) and Bacillus pumilus (UFPEDA 472) on the contribution of biomass, the concentration of nitrogen (N) compounds and BNF. The experiment was carried out under greenhouse conditions with pots containing washed and autoclaved sand. Mung bean seeds were inoculated or coinoculated (double or triple) with Bradyrhizobium, A. baldaniorum and/or Bacillus pumilus, and one absolute control (not inoculated) was used. The experimental design was a completely randomized design with 21 treatments harvested in two different periods (flowering and pod maturation). Inoculation and coinoculation positively influenced the number of nodules, shoot dry weight, N accumulated, total N content and inorganic and organic compounds (free ammonia, nitrate, ureides and leghemoglobin), indicating that there was efficiency in BNF and synergistic interaction between the bacteria used and the mung bean plants. Inoculation with Bradyrhizobium species and the combination of these strains with A. baldaniorum and Bacillus pumilus positively influenced N fixation and metabolism in mung bean plants, especially when B. elkanii BR 2003 and B. pachyrhizi BR 3262 were used.