Beet poleroviruses: close friends or distant relatives?

UNLABELLED SUMMARY Taxonomy: There are three members of the genus Polerovirus (family Luteoviridae) that induce yellowing of sugar beet: Beet mild yellowing virus (BMYV), Beet chlorosis virus (BChV) and Beet western yellows virus-USA (BWYV-USA, Fig. 1). Non-beet-infecting isolates of BWYV found particularly within Europe have now been re-named Turnip yellows virus (TuYV). Species-specific antibodies are unavailable, but the viruses can be distinguished by RT-PCR using primers specifically designed to the 5' end of their respective genomes. Physical properties: The isometric virus particles are approximately 26 nm in diameter and the genome consists of a single strand of positive sense RNA that utilizes almost all known plant virus gene expression strategies (initiation bypass, translational frameshifting and readthrough, synthesis of subgenomic RNA and proteolytic processing). HOST RANGE Many members of the Chenopodiaceae are susceptible, including commercial crops of sugar beet (Beta vulgaris), red beet and spinach. Experimental hosts include Montia perfoliata, Nicotiana benthamiana and Arabidopsis thaliana. SYMPTOMS Sugar beet infected with beet poleroviruses show patches of chlorosis on the older leaves 4-6 weeks post-infection; these areas expand until the whole leaf becomes yellow and older leaves then tend to thicken and become brittle. TRANSMISSION Beet poleroviruses are transmitted in a persistent (circulative, non-propagative) manner by several different aphid species, Myzus persicae being the most important vector.