Author: Jane R. Smith
Author affiliation: The Ohio State University (graduate student)
Investigating the role of Pseudomonas in soybean pathogen growth inhibition
Agrobacterium rhizogenes is the plant-pathogenic bacterium causative agent of hairy root disease on many dicotyledonous plants. A. rhizogenes harbors a root-inducing (Ri) plasmid which contains a region of DNA that is transferred (T-DNA) from the bacteria into the host chromosome. After T-DNA incorporation, the transformed plant cells grow and divide to produce transgenic roots. These roots alter the plant source-sink relationship to favor root growth. Since chemical control of bacterial diseases via antibiotics is highly regulated, we seek alternative ways to control the disease. We have been studying the ability of 52 Pseudomonas strains in inhibit A. rhizogenes growth in vitro and in planta. In our in vitro experiments, 14 Pseudomonas strains were able to inhibit pathogen growth. These strains were selected for in planta assays (on Kalanchoe and soybean). In Kalanchoe, three strains (1B1, 93G8 and 48G9) were able to reduce the incidence of disease compared to controls. These three strains were used to inoculate soybean composite plants. As expected, these strains were able to reduce the transgenic roots formation up to 95% compared to the control. We also examined Agrobacterium persistence in these soybean cuttings. Pseudomonas treatments were able to reduce Agrobacterium numbers by nearly 1000-fold. Taken together, these results suggest that the certain Pseudomonas strains have the ability to inhibit Agrobacterium rhizogenes growth and disease development and can be used in the management in the future.