First Report of <i>Ralstonia pseudosolanacearum</i> (Phylotype I) Causing Bacterial Wilt in <i>Zingiber officinale</i> in Slovenia

In September 2023, symptoms of bacterial wilt were observed in ginger (Zingiber officinale) plants in two greenhouses in Zreče, Savinjska region, Slovenia. Affected plants exhibited symptoms such as leaf yellowing, wilting, and stem browning, eventually progressing to dieback. Rhizomes exhibited brown vascular discoloration, with tissue softening and maceration, and milky-white exudates. In one greenhouse, an incidence of up to 80% of the plants was observed. Bulk samples (three plants per greenhouse) were surface disinfected with 70% ethanol. Extracts were prepared separately from rhizomes and stems, plated on a modified SMSA medium (mSMSA; Elphinstone et al., 1996) and incubated at 28 °C for three days. Colonies characteristic of the Ralstonia solanacearum species complex (RSSC) on mSMSA were isolated from all samples. Four isolates were purified and characterized on mSMSA, TSBA (BD Difco™, Cat. No. 211768), and SPA (Hayward, 1960) media. Real-time PCR (Vreeburg et al., 2016) was employed to confirm the identity of the strain as RSSC, and conventional PCR using primers Rs-1-F/Rs-3-R (Pastrik et al., 2002) was used to identify the pathogen as Ralstonia pseudosolanacearum Safni et al., 2014. Sequevar determination using egl gene sequencing (EPPO, 2021) showed 100% identity with 100% coverage to strain RUN 6824 from ginger in Germany (GenBank OQ753212), confirming phylotype I, sequevar 30 (Cellier et al., 2023). The sequences were deposited in GenBank (accessions: PV358607–PV358610). The pathogenicity of two selected ginger isolates was assessed by inoculating five tomato (Solanum lycopersicum cv. Moneymaker) plants per isolate. The stems were pricked with a sterile needle dipped in 24-h-old cultures grown on CPG medium (Schaad et al., 2001). Positive controls (R. solanacearum NCPPB 4156 and R. pseudosolanacearum GBBC 1112 (ILVO Plant Clinic, Merelbeke, Belgium) and a negative control (sterile needle) were included in the study. Wilting symptoms appeared within 2 days. Ginger isolates caused partial to complete wilting by 14 days post-inoculation. Plants were incubated in a growth chamber at 28°C (day), 25°C (night), and 80% humidity. Ginger isolates NIB Z 3683 and NIB Z 3685, from this study, initially induced more severe wilting than positive controls. Fourteen days post inoculation (pricking) positive controls caused plant death, while ginger isolates led to partial or complete wilting, affecting most leaves except the top parts of the inoculated plants. The negative control remained asymptomatic. The pathogen was successfully reisolated from infected plants and identified by real-time PCR (Vreeburg et al., 2016). This is the first report of R. pseudosolanacearum causing bacterial wilt of ginger in Slovenia. Traceability analysis suggests indirect introduction via imported rhizomes from Peru. Official eradication measures were taken, including destruction of all plants, disinfection, and a three-year host-plant ban. Ongoing annual monitoring is conducted in and around the affected area. As the cultivation of ginger is constantly increasing in Europe, this report underscores the need for vigilant monitoring and phytosanitary control of imported rhizomes to prevent further spread of this regulated pathogen.