Letter to the Editor: The Ralstonia research community rejects the proposal to classify phylotype I Ralstonia into the new species Ralstonia nicotianae

The Ralstonia solanacearum species complex (RSSC) is a group of globally important plant pathogens. Bacteria in this very large and genetically diverse group all colonize the xylem elements of angiosperm plants and cause high-impact wilting diseases of many crops. Because they threaten economic and food security, several RSSC subgroups are strictly regulated as quarantine pests (See “Regulation” section of References). Biologically meaningful and consistent nomenclature is essential for organisms that have major economic and regulatory importance like plant pathogenic Ralstonia. There are currently three species of Ralstonia wilt pathogens: R. pseudosolanacearum (corresponding to two phylogenetic groups that are described in the literature as phylotypes I and III), R. solanacearum (phylotypes IIA, IIB, and IIC), and R. syzygii (phylotype IV, containing three subspecies: subsp. syzygii, subsp. celebensis, and subsp. indonesiensis). A recent paper proposed re-classifying phylotype I as a new species named “Ralstonia nicotianae” (Liu et al. 2023). The purpose of this commentary is to register our objection to the taxon “Ralstonia nicotianae”.