Breeding for improved nitrogen fixation : Improving soybean x Bradyrhizobium symbiosis for cool growing regions

Protein yield of soybean depends heavily on successful symbiosis with Bradyrhizobium bacteria able to fix atmospheric nitrogen. Low temperature limits the growth of soybeans but also the efficiency of biological nitrogen fixation (BNF). Cold tolerant Bradyrhizobium strains could be identified, and significant differences in BNF were found for Bradyrhizobium and for soybean genotypes allowing selection for improved BNF. Significant soybean x Bradyrhizobium interactions were found in mesocosm and field trials, as well as complex temperature dependent interactions with mycorrhiza strains. More studies are needed to elucidate the important plant – rhizosphere interactions.