Ralstonia solanacearum (phylotype II) isolated from Rosa spp. in the Netherlands is closely related to phylotype II isolates from other sources in the Netherlands and is virulent on potato

In 2018, during an annual survey in the Netherlands, Ralstonia solanacearum phylotype II (phy II) was found in asymptomatic greenhouse rose plants at three geographic locations. These findings were remarkable, since previous findings of Ralstonia sp. in rose always concerned Ralstonia pseudosolanacearum phylotype I (phy I). Therefore, no information was available on the virulence of R. solanacearum phy II on rose. In this study, R. solanacearum phy II isolates PD 7421 and PD 7394, isolated in 2018 from asymptomatic ornamental rose (Rosa spp.), were assessed for their virulence in two rose cultivars ("Armando" and "Red Naomi") at two temperatures. No typical symptoms were observed for PD 7421 and PD 7394 on the two rose cultivars, irrespective of the temperature. However, latent infections upon inoculation of these isolates on rose did occur. R. solanacearum phy II is known as a major potato pathogen, where it causes brown rot. Whole genome multilocus sequence typing analysis demonstrated that the isolates from rose were closely related to R. solanacearum phy II isolates previously found in seed potato and surface water in the Netherlands. Because of this close genetic relatedness, the virulence of PD 7421 and PD 7394 was also assessed in potato plants, where both isolates caused severe disease symptoms on the shoots as well as the daughter tubers. This implies that rose can act as a reservoir for R. solanacearum phy II and, in this way, can potentially be involved in spreading this bacterium.