The goal of this proposal is to develop a modified strain of BBradyrhizobium japonicum that continues to provide all the nitrogen-fixing benefits of nodulation and does not suppress soybean plant defense against other microbes (i.e. disease-causing pathogens) and potentially the soybean cyst nematode as well. Development of such a strain would enhance the disease resistance of nodulated soybeans, hence, providing obvious benefits for the farmers.

Develop a modified strain of Bradyrhizobium japonicum that continues to provide all the nitrogen-fixing benefits of nodulation and does not suppress soybean plant defense against other microbes such as disease-causing pathogens or the soybean cyst nematode as well.

Update:
In the past six months, we discovered that B. japonicum makes GA most strongly during the flowering stage of soybean. Given that our previous studies were largely focused on earlier stages, we have verified that the ga- knock-out strain is still able to fix nitrogen and enable soybean plant growth in an equivalent manner to the parental GA+ B. japonicum through the flowering stage. In addition, we have begun preliminary experiments for each of the three project objectives outlined above, specifically concentrating on plants in the flowering stage. While the experiments for PRR and SCN have only just begun, we do have data for SDS indicating that soybean plants nodulated with the ga- knock-out strain is significantly more resistant to SDS than those nodulated with the parental GA+ B. japonicum. We are currently growing additional plants to repeat the SDS infection experiments and further verify this effect. Nevertheless, particularly given the impact of SDS and potential further extension of this effect to other diseases as well, we are quite excited by this result and are exploring all avenues towards expeditious advancement of this biotechnical concept to agricultural application.

In the past year, we discovered that B. japonicum makes GA most strongly during the flowering stage of soybean. Given that our previous studies were largely focused on earlier stages, we have verified that the ga-­- knock-­-out strain is still able to fix nitrogen and enable soybean plant growth in an equivalent manner to the parental GA+ B. japonicum through the flowering stage. In addition, we have carried out experiments for each of the three project objectives outlined above, using plants both just before and in the flowering stage. Our data for SDS indicates that soybean plants nodulated with the ga-­- knock-­-out strain are significantly more resistant to SDS than those nodulated with the parental GA+ B. japonicum if infected before, but not during, the flowering stage. We are currently repeating these experiments to verify and further investigate the effect of plant developmental stage.
Nevertheless, given that the tested diseases target seedlings, we remain optimistic that this approach may be of agricultural utility.