Study of sugar beet viruses transmitted by Polymyxa betae in the Czech Republic

Sugar beet viruses transmitted by Polymyxa betae are very widespread in the Czech Republic. Beet soil-borne virus (BSBV) is present in almost all fields used for sugar beet growing, beet virus Q (BVQ) is present in about 50% of fields but beet necrotic yellow vein virus (BNYVV) is present in some limited regions only. It means that mixed infections of sugar beet by at least two viruses are quite common in the field. P. betae also occurs in almost all fields where sugar beet is now grown. Only two populations of P. betae not transmitting any virus were found. Cystosori of P. betae can harbour viruses without loosing infectivity for a very long time. We were able to detect these viruses in plants grown in soil stored dry for 12 years. BNYVV can cause serious yield losses under mideuropean conditions reaching up to 50% of sugar yield, whereas harmfulness BSBV and BVQ is questionable, because they also occur in fields with no problems concerning sugar beet growing. The host range of these viruses was studied. Both infect all types of beet (sugar fodder, red beet, mangold) and spinach and usually are detectable in root system only. Other chenopodiaceous plants are infected only by some virus strains. These strains are also able to spread into above-ground parts of plants.