RESUMEN
Rhizomania is a viral disease, caused by beet necrotic yellow vein furovirus (BNYVV), which was detected in Spanish sugar beets in 1988, it being focused on the Castilla y León region. BNYVV has five RNA fragments with specific functions, and the different composition and proportion of RNA in the virions allow their separation and the characterization of their activities during the development of the disease. Thirty-six samples of sugar beet rootlets and frozen pulps from three different sugar beet zones of Castilla y León were analyzed by DAS-ELISA and Immunocapture-Reverse Transcription-Polymerase Chain Reaction (IC-RT-PCR) using specific primers. The identity of the cDNA products was confirmed by nested-PCR and restriction fragment length polymorphism (RFLP). The uniformity of the patterns obtained by RFLP analyses with nine endonucleases showed the existence of a unique strain of BNYVV in 80,000 Ha of crop surface which could be explained by a recent arrival of the rhizomania disease to this region. The isolates studied were more similar to type A, which has been previously described in BNYVV, but a non-expected cleavage site for this molecular group was observed with endonuclease HincII on the RNA-2 IC-RT-PCR product (nt 2133-3293) in the thirty-six Spanish samples and also in a North American strain taken as reference. The use of frozen pulps obtained as a previous step to the industrial extraction of sugar avoids problems due to erratic distribution of the virus in the roots, provides repetitive results for a particular sample, and facilitates epidemiological and distributional studies on rhizomania disease.