First Report of Bacterial Wilt of Ginger Caused by Ralstonia pseudosolanacearum in the Continental United States
Authors: Chiu Milo , Lowe-Power Tiffany , Grabowski Michelle , Khokhani Devanshi 
Published: January 2025

Ginger (Zingiber officinale) is an herbaceous perennial in the Zingiberaceae family grown primarily in tropical to subtropical biomes as a culinary spice, a traditional medicine, and a landscaping plant. While ginger grows at soil temperatures above 20°C, several farmers in the upper Midwestern US farmers grows short-season ginger in high tunnels. In 2023 and 2024, growers in southeastern Minnesota reported a new disease of ginger. USDA traced the origin of the ginger rhizomes imported by these growers to Peru (Soto-Heredia et al., 2024). Plants exhibited wilting, chlorosis, pseudostem collapse, and plant death. Rhizomes were squishy with a fetid, rotting odor. Disease incidence ranged from scattered plants to 50% of the crop. Symptomatic samples tested positive for Ralstonia solanacearum species complex (RSSC) using AgDia ImmunoStrips. Rhizome tissue extracts plated onto CPG + 1% tetrazolium chloride agar and mSMSA agar produced irregular, round-to-fluidal white colonies with pink centers after 48 h of incubation at 28°C (Kelman 1954; Engelbrecht 1994). Diagnostic RSSC phylotype-specific multiplex PCR primers Nmult21:1F, Nmult21:2F, Nmult23:AF, Nmult22:InF, Nmult22:RR, and 759f/760r confirmed isolate identity; two isolates (UMN24-1, UMN24-2) yielded bands at 280 bp and 144 bp, identifying them as RSSC and phylotype I respectively (Fegan and Prior 2005; Opina et al. 1997). Additionally, 16S rRNA PCR of these isolates was sequenced using primers 27F (5’-AGAGTTTGATCMTGGCTCAG-3’)/1492R (5’-TACGGYTACCTTGTTACGACTT-3’) and shared >99% identity (isolate UMN24-1: 99.00% 27F, 99.53% 1492R; UMN24-2: 99.32% 1492R) with R. pseudosolanacearum (Rps) strain Gj707 (GenBank CP104497.1). Eight ginger plants in individual pots were grown in a Conviron growth chamber (28°C, 250 μmol/m2/s, 16 h photoperiod) and inoculated at the six-leaf stage (6 weeks old) by pipetting 109 CFU of the isolate, UMN24-1, suspended in sterile water into a 30°angled 1 cm incision on the pseudostem. We scored disease incidence based on wilted leaves per total leaves on each plant for 14 days post inoculation (dpi). While control plants remained healthy, inoculated plants showed symptoms (wilting, vascular discoloration, chlorosis) at 4 dpi, were 100% wilted by 6 dpi, and all pseudostems completely collapsed by 11 dpi (Fig. S1). Bacteria recovered from the inoculated plants matched the original isolate in appearance and positively identified as RSSC phylotype I using the PCR analyses described above. To confirm taxonomic identification of UMN24-1, the complete genome of this isolate was sequenced using hybrid Illumina and Oxford Nanopore sequencing (NCBI BioProject ID PRJNA1178296, release date upon publication) (Fig. S2). Average nucleotide identity (ANI) analysis of UMN24-1 using KBase’s FastANI app reported 99.8% identity shared with Japanese RSSC phylotype I strain MAFF311693 (GenBank GCF 015698385.1). We also sequenced UMN24-2, and its phylogenetic analysis revealed that the two isolates are clonal (Fig. S2). Hence, we did not submit its sequence to the NCBI. This marks the first documented case of Rps in ginger in the United States. Similar to bacterial wilt in ginger closely related crop like turmeric has been repeatedly reported in northern Europe in recent years (EPPO 2024). While RSSC phylotype I is geographically limited by its minimal cold tolerance, the emergence of a pathogen with a potentially broad host range has worrying implications in a changing climate.