Dynamic ecological interactions of two quarantine-concern Ralstonia strains in river water and plants

Abstract Plant pathogenic Ralstonia belonging to the IIB-1 (“race 3 biovar 2”) and I-33 (rose) subgroups are emerging quarantine and biosecurity threats. Both strains have been introduced to Europe, where they persist in weedy plants and surface water and cause occasional costly disease outbreaks. We combined in planta, in vitro, and environmental water microcosm experiments to determine if these two concerning strains are likely to co-exist in environments where they have become established or if one might be expected to displace the other. Using a representative strain from each subgroup we investigated the dynamics and fitness of these two Ralstonia pathogens across ecologically relevant environments. Interactions between the strains were context dependent: the presence of a competing strain had little impact on bacterial survival in river water microcosms, but the I-33 strain had a fitness advantage in wilt susceptible tomato plants. We found no evidence of direct growth inhibition by either strain in vitro. The IIB-1 strain persisted longer than I-33 in cool temperature river water microcosms. Warmer temperatures extended the culturability of both strains, which may be important as climate change warms surface water globally. Additionally, Ralstonia strains persisting in 20°C water microcosms for 6 months were still able to cause disease in tomato plants. Together, our results provide useful insight into the dynamics of these two strains in environments where they are currently established, which may inform management practices moving forward. Competing Interest Statement The authors have declared no competing interest.