At least 20 tymovirus species are known. The generic acronym, tymovirus, comes from t urnip yellow mo saic virus (TYMV), the name of the first to be described (1 ), now the type species. The tymoviruses infect dicotyledonous angiosperms, mostly those that have the C3 photosynthetic pathway; few have been recorded in crop plants, and none are known to infect monocotyledonous angiosperms. They cause bright yellow mosaics, vein-clearing, and mottling. Their natural vectors, when known, are beetles, mostly halticid or galerucid flea beetles. Only four tymoviruses have been recorded as seed-borne (2 ).