LAUSR

Ralstonia pseudosolanacearum, a European Union quarantine organism, was until recently absent in the aquatic environments and outdoor cultivation systems inside the region. This bacterium was only sporadically reported in restricted greenhouse cultivation systems in some EU countries. In this paper we report the first findings of R. pseudosolanacearum (phylotype I) in surface water in two distinct geographic locations in the Netherlands in 2020. In 2021, the population of Ralstonia pseudosolanacearum in surface water was ranging between 104 - 106 CFU/l. An inoculum reservoir for R. pseudosolanacearum in these aquatic environments was the wild bittersweet plant where population densities were ranging from 105 - 107 CFU/ml concentrated bittersweet extract. The virulence of the R. pseudosolanacearum isolates from surface water and bittersweet was confirmed by a pathogenicity test on Solanum lycopersicum cv. Moneymaker plants, resulting in wilting and necrosis of the plants. Sequence analysis of the egl locus of R. pseudosolanacearum isolates from surface water and bittersweet revealed that these isolates are closely related to R. pseudosolanacearum (phylotype I) isolates found previously in the Netherlands on rose. R. pseudosolanacearum (phylotype I) has a very broad host plant range, including potato, many ornamental and other economically important crops. This highlights the risk for various host plants grown in the vicinity of the geographic locations where R. pseudosolanacearum has been found and shows the importance of unraveling the epidemiological parameters of the survival, establishment and spread of R. pseudosolanacearum in temperate climates.