The high demand for high-quality soybean products can partly be covered with domestic production providing that efforts are made to breed soybean cultivars specifically adapted to cooler growing regions. Within this project crosses will be performed in order to develop new soybean breeding lines. The latter will be tested in the field together with a large scale multi-location variety testing under organic and conventional management. The breeders aim at developing an efficient soybean breeding strategy for various end uses. They will focus on the development of soybean genotypes for tofu and fodder with following properties: day length independent, high quality, high cold tolerance, weed-competitive/tolerant, early ripening and high biological nitrogen fixation. Thereby the nitrogen fixation always depends on the very complex interactions between the soybean genotype and the Bradyrhizobia strains, the soil physical parameters as well as the total amount of soil microorganisms.
Soybean has gained significant attention in Europe for the production of high quality protein for human consumption as well as for feed in recent years. Under climatic conditions such as Central Europe, low temperature is the major factor limiting soybean growth and symbiotic nitrogen fixation. Therefore, the biological nitrogen fixation shall be improved by breeding for cold tolerant soybean genotypes and by selecting adapted Bradyrhizobia strains. The aim of the study is to identify (i) Bradyrhizobia strains that show improved nodulation under cool growing conditions and (ii) Bradyrhizobia x soybean interactions that can be exploited for breeding for improved symbiosis.
In pot trials we have tested twelve different Bradyrhizobia inoculants and one inactivated control on three early soybean varieties (maturity group 000) at three different temperature regimes (14/10°C; 16/12°C; 22/20°C). The number of nodules, root and shoot biomass as well as chlorophyll content were assessed after six weeks. In parallel four commercially available inoculants and one non-inoculated control were tested on the three soybean varieties under organic and conventional growing conditions in Central Germany. Number of nodules was assessed six weeks after sowing and at beginning of flowering. Yield, thousand kernel weight and protein content were assessed at harvest. The most promising Bradyrhizobia strains from the pot trial have been multiplied and are currently tested on 20 different soybean varieties under 16/12°C temperature regime and will be verified in field trials in 2013 and 2014.
Coordination of Soybean-Bradyrhizobia pot trials and field trials