The Continuing Saga of Rhizomania of Sugar Beets in the United States.

Abstract

Historically, Beet necrotic yellow vein virus (BNYVV), which causes the disease rhizomania of sugar beet, has caused major reductions in root yield and quality wherever it occurred. In the United States, the disease was first identified in California in 1984 (12), but it now occurs in every major sugar beet production region in the country. Fortunately, strong genetic tolerance to BNYVV, conferred by the Rz1 gene, was identified soon after rhizomania was discovered in the United States, and it has been incorporated into regionally adapted cultivars that allow profitable sugar beet production in areas infested with the pathogen. Plants possessing Rz1 are susceptible to infection by P. betae and BNYVV, but virus titers remain low, and typically, infected plants exhibit normal, asymptomatic growth. However, in the Imperial Valley of California in 2002, plants in a field planted to a rhizomaniatolerant cultivar began to express symptoms of rhizomania (47). Large strips of diseased plants occurred across the field, and it was soon verified that certain isolates of BNYVV from the California Imperial Valley (CIV-BNYVV) had overcome genetic resistance. In other regions of the United States, individual plants, or clusters of plants, in fields planted to rhizomaniatolerant cultivars have also become infected by BNYVV and developed diagnostic symptoms of severe rhizomania. Although patterns of disease development have varied between California fields and those in other production regions in the United States, the breakdown of genetic resistance has caused considerable concern among those involved in sugar beet production. The purpose of this article is to provide an update on rhizomania and the activities that are currently underway to manage this continuing threat to the U.S. sugar beet industry. A review on the detection and distribution of rhizomania and soilborne viruses associated with sugar beet production in the United States (61), and a second more in-depth review on BNYVV and its vector, Polymyxa betae (Keskin) (60), have been published.