Exploring the genetic diversity of recent Ralstonia pseudosolanacearum phylotype I findings in Europe

The increasing prevalence of Ralstonia pseudosolanacearum phylotype I (phy I) in agricultural regions across Europe highlights the need for heightened awareness and preventive measures. Recent detections in multiple European countries span a range of agricultural systems, host plants, and natural aquatic environments. These findings have been linked either to infected plant material at import (interceptions) or to plants cultivated in specific European regions, often after importation of infected plant material. To investigate the genetic diversity of these emerging populations, we analysed whole-genome sequence (WGS) data from a collection of 62 R. pseudosolanacearum phy I isolates, including those recently obtained in various European countries, using average nucleotide analysis (ANI) and core genome multilocus sequence typing (cgMLST). ANI analysis revealed two distinct major clades: the "rose clade", comprising isolates from rose, potato, surface water, and bittersweet, most closely matching with sequevar 33, and the "major ginger clade", including isolates from members of the Zingiberaceae family, with the best match to sequevar 30. Additionally, several minor clades of Zingiberaceae isolates and a "tomato clade” (most closely related to sequevar 18) were identified. Pathogenicity assays with high inoculation titers were performed on tomato to assess the biological relevance of the observed genetic diversity. Our findings suggest multiple independent introduction events of virulent R. pseudosolanacearum phy I populations into Europe between 2015 and 2024. Given the genetic variability of the introduced bacterial isolates, the pathogen’s ability to systemically infect a broad range of host plants which can differ per isolate, and its persistence in diverse agricultural and environmental niches, the implementation of stringent import control measures for plant material entering the European Union is strongly recommended.