Revision on the taxonomy on Curtobacterium flaccumfaciens
Curtobacterium flaccumfaciens pv. flaccumfaciens (EPPO A2 List) causing bacterial wilt of Fabaceae (such as Phaseolus vulgaris, Glycine max, Vicia faba) is regulated by a number of countries worldwide.
Recent research by Osdaghi et al. showed that strains pathogenic to beans are assigned to three species: Curtobacterium flaccumfaciens, Curtobacterium poinsettiae and Curtobacterium aurantiacum.
Curtobacterium flaccumfaciens pv. flaccumfaciens corresponds to strains pathogenic on Fabaceae with yellowish appearance on common nutrient media. These strains are found on all continents.
Curtobacterium poinsettiae primarily corresponds to strains pathogenic on poinsettia (Euphorbia pulcherrima). These strains show an orange/salmon appearance on common nutrient media. The species also contains strains pathogenic on Fabaceae. A pathovar designation should still be given to these strains (e.g. C. poinsettiae pv. fabae). C. poinsettiae is the elevation to species level of Curtobacterium flaccumfaciens pv. poinsettiae which has caused bacterial wilt of poinsettia in the USA since the 1950s and 1960s. There is no published record on its presence in the EPPO region.
It may be noted that the current strains of Curtobacterium pathogenic on poinsettia present in Europe are assigned to Curtobacterium flaccumfaciens. A pathovar designation should still be given to these strains (e.g. C. flaccumfaciens pv. euphorbiae).
Curtobacterium aurantiacum is a new species. So far, all strains in this species are pathogenic on bean (Phaseolus vulgaris) and have a reddish appearance on common nutrient media. So far, these strains are only found in Iran.
It may be noted that these new taxonomic names were effectively published but not validly published under the rules of the International Code of Nomenclature of Prokaryotes (Bacteriological Code) and they still await validation.
However, as these changes have practical implication for quarantine purposes, they have been implemented in EPPO Global Database, with a new code created for Curtobacterium aurantiacum. The EPPO Standard PM 7/102 Diagnostic protocol for Curtobacterium flaccumfaciens pv. flaccumfaciens is being revised.
Sources
Osdaghi E, Taghavi SM, Hamidizade M, Kariminejhad M, Fazliarab A, Maleki HH, Baeyen S, Taghouti G, Jacques M-A, Van Vaerenbergh J & Portier P (2024) Multiphasic investigations imply transfer of orange-/red-pigmented strains of the bean pathogen Curtobacterium flaccumfaciens pv. flaccumfaciens to a new species as C. aurantiacum sp. nov., elevation of the poinsettia pathogen C. flaccumfaciens pv. poinsettiae to the species level as C. poinsettiae sp. nov., and synonymy of C. albidum with C. citreum. Systematic and Applied Microbiology 47, 126489. https://doi.org/10.1016/j.syapm.2024.126489
EPPO Panel on Diagnostic in Bacteriology and European Reference Laboratory (EURL) for pests on plants - bacteria (2025-02).