Beet yellows virus (BYV), the type member of the genus Closterovirus and one of the most economically important yellowing viruses, causes serious losses in sugar beet. BYV causes yellowing, thickening and brittleness on lower and middle leaves. During a survey in 2006 and 2007 beet leaves showing yellowing symptoms were collected from sugar beet fields in Isfahan and Charmahal-O-Bakhtiari provinces. Double antibody sandwich ELISA (DAS-ELISA) using commercial polyclonal antiserum against BYV (DSMZ, Germany ) was used to detect the virus. In DAS-ELISA 34 out of 260 samples from Isfahan and 21 out of 226 samples from Charmahal-O-Bakhtiari were tested positive. Total RNA of ELISA positive samples were extracted and used as template in RT-PCR using specific primers of BYV (BYVA/B, BYVA/C and BYVY/Z primer pairs). All the Isfahan samples amplified approximately expected sizes of 350 bp, 560 bp and 670 bp using BYVA/B, BYVA/C and BYVY/Z primer pairs, respectively. None of the Charmahal-O-Bakhtiari samples amplified expected segments. The 350 bp and 670 bp PCR products and a 1615 bp PCR product amplified (using BYVA/Z primer pair) of Lavark isolate were cloned and sequenced. The BLAST comparison revealed high similarity between nucleotide sequences of Lavark isolate and those of other BYV isolates available at GenBank. Pairwise nucleotide sequence alignment of 1615 bp segment with full length sequence of BYV Ukraine isolate showed that it is corresponding to ORF6, ORF7 and ORF8 of BYV genome. Comparison of deduced amino acid sequence of ORF6, ORF7 and ORF8 with those of BYV Ukraine isolate showed 93.63%, 98.89% and 96.05% identity, respectively. Phylogenetic analysis of amino acid sequence of coat protein gene (ORF6) revealed closer relationship between BYV Lavark isolate and BYV Ukraine isolate than other BYV isolates available at GenBank. In virus transmission test, the virus was transmitted to sugar beet and spinage by Aphis fabae . Infection of tests plant was confirmed by RT-PCR.
