A New Report of Rhizomania and Other Furoviruses Infecting Sugar Beet in Minnesota.

Several fields planted in sugar beet (Beta vulgaris) in the Southern Minnesota Beet Sugar Cooperative growing area showed patches of pale greenish yellow foliage and upright leaves characteristic of rhizomania. Other symptoms included reduced root size and root proliferation. Samples taken from these areas during August of 1996 were evaluated for beet necrotic yellow vein virus (BNYVV), the cause of rhizomania, and for other sugar beet furoviruses. BNYVV was identified in 59 of 90 beet samples tested with enzyme-linked immunosorbent assay and Western blot (immunoblot) analyses (molecular mass approximately 22 kDa) with specific (polyclonal antisera donated by K. Richards; monoclonal antisera donated by G. Grassi) and broadly reactive antisera produced at the USDA in Salinas, CA. Recovery by mechanical inoculation of Chenopodium quinoa and Beta macrocarpa confirmed identity. Beet leaves showing symptoms of vein clearing, vein banding, mosaic, and vein necrosis were all identified as being infected with beet soilborne mosaic virus (BSBMV). No systemic leaf symptoms of BNYVV were found in any sample. The BSBMV isolates were identical to one another based on symptomatology of indicator plants and molecular masses in Western blots (approximately 24 kDa), but symptoms were distinct from those of other members of the BSBMV serogroup isolates previously studied from Texas, Idaho, Nebraska, and Colorado. The beet soilborne virus (BSBV) was also recovered by mechanical inoculation and Western blot analysis (antisera donated by R. Koenig) in three samples of field-collected beets. This is a new report of BNYVV, BSBMV, and BSBV in Minnesota. The distribution of rhizomania in infested fields was not isolated to any general area, which indicates that the virus has been present and multiplying in previous sugar beet crops and was not detected. Severity of infection ranged from mild root symptoms with near normal yields and sugar content, to moderate and severe root symptoms with low yields and low sugar content.