Getting wild with bradys

Abstract

Mungbeans are often poor nitrogen fixers compared with other legumes. We investigated whether some wild bradyrhizobia strains may be equal or superior to the commercial inoculum, CB1015, in promoting mungbean growth or nitrogen fixation under a series of abiotic stresses. Three experiments were conducted under glasshouse or growth cabinet conditions, comparing the performance of mungbean plants when inoculated with CB1015 and wild bradyrhizobia collected from north Queensland. Plants were exposed to neutral and acid soil conditions, high and low air temperatures, and two water deficit regimes.
Under both acid and neutral soil conditions, thirteen of the fifteen strains evaluated promoted growth at least as well as CB1015. Two wild strains significantly outperformed CB1015 under neutral conditions. Though differences were found under acid conditions, no wild bradyrhizobia were significantly superior to CB1015. Under both high and low temperature conditions, most of the eleven wild strains evaluated promoted mungbean growth at least as well as CB1015. Some wild bradyrhizobia significantly outperformed CB1015 for fixed nitrogen in shoots per pot. Some performed well at the high temperature (35°C), some at the low temperature (21°C), and some at all temperatures tested (21°C, 28°C, 35°C).
At least seven of the fourteen wild bradyrhizobia evaluated performed as well as CB1015 in well-watered conditions and both drought treatments. Combined, these findings suggest that gains could be made in mungbean performance through use of better adapted bradyrhizobia and that there may be significant untapped resources of wild bradyrhizobia that could be exploited to improve performance of cultivated mungbeans in northern Australia.