Biological, serological, and molecular variability suggest three distinct polerovirus species infecting beet or rape

Yellowing diseases of sugar beet can be caused by a range of strains classi fied as Beet mild yellowing virus (BMYV) or Beet western yellows virus (BWY V), both belonging to the genus Polerovirus of the family Luteoviridae. Hos t range, genomic, and serological studies have shown that isolates of these viruses can be grouped into three distinct species. Within these species, the coat protein amino acid sequences are highly conserved (more than 90% h omology), whereas the PO sequences (open reading frame, ORF 0) are variable (about 30% homology). Based on these results, we propose a new classificat ion of BMYV and BWYV into three distinct species. Two of these species are presented for the first time and are not yet recognized by the Internationa l Committee on Taxonomy of Viruses. The first species, BMYV, infects sugar beet and Capsella bursa-pastoris. The second species, Brassica yellowing vi rus, does not infect beet, but infects a large number of plants belonging t o the genus Brassica within the family Brassicaceae. The third species, Bee t chlorosis virus, infects beet and Chenopodium capitatum, but not Capsella bursa-pastoris.