General Features of Beet Necrotic Yellow Vein Virus

Abstract

Beet necrotic yellow vein virus (BNYVV), identified as the causal agent of rhizomania of sugar beet in the early 1970s, is transmitted by the soil-borne protist Polymyxa betae and by inoculation of sap to most species of the family Chenopodiaceae and several species of a few other families. BNYVV, the type member of the genus Benyvirus in the family Benyviridae, has rod-shaped particles and four to five single-stranded, positive-sense RNA genomes. RNA1 and RNA2 encode the essential elements for replication, assembly, transmission, and cell-to-cell movement; smaller RNA segments, RNA3, RNA4, and RNA5, are associated with vector-mediated infection and disease development in sugar beet roots. RNA3 is required for development of rhizomania symptoms in sugar beet, whereas RNA4 is important for efficient vector transmission. RNA5 is associated with the severity of symptom development in sugar beet roots, but is dispensable for BNYVV survival. Synergistic effects on symptom development and vector transmission efficiency have also been found between RNA3 and RNA4 and between RNA5 and RNA4. Symptom expression has been suggested to involve auxin-induced genes during BNYVV infection. BNYVV is usually confined to root systems of sugar beet. This restricted distribution of the virus in the root is attributed to barriers that block virus movement between vascular and nonvascular tissues in roots. Enzyme-linked immunosorbent assay (ELISA) is the best method for rapid diagnosis of large numbers of samples. Reverse transcriptase polymerase chain reaction (RT-PCR) and improved-RT-PCR methods are more sensitive and specific for distinguishing BNYVV strains. Other soil-borne RNA viruses can be present in sugar beet roots, some of which are occasionally associated with rhizomania.