Beet necrotic yellow vein virus (BNYVV), the cause of rhizomania. (a) Electron micrograph of BNYVV particles [courtesy Descriptions of Plant Viruses No. 391 (Tamada, 2002), http://www.dpvweb.net/dpv/showdpv.php?dpvno=391, with permission from the Association of Applied Biologists). Scale bar represents 100 nm. (b) BNYVV genome map showing multipartite organisation of viral proteins. CP, coat protein; HEL, helicase; MTR, methyltransferase; POL, polymerase; PRO, protease; RT, read‐through protein.