Members of the genus Polerovirus ( Luteoviridae ) that cause yellowing in sugar beet consist of three species, Beet mild yellowing virus (BMYV), Beet western yellows virus (BWYV) and Beet chlorosis virus (BChV). For detection and determination of certain molecular properties of poleroviruses infecting sugar beet during 1385-1386, 571 leaf samples of sugar beet with yellowing and thickening symptoms in older leaves were collected from sugar beet fields at Isfahan and Charmahal-o-bakhtiary provinces. Samples were tested using a polyclonal BWYV antibody in DAS-ELISA technique. None of samples in Chahar mahal-o-bakhtiary province were infected to poleroviruses of infecting sugar beet. Of the 290 Isfahan samples tested, 5 samples recognized infected to polerovirus by DAS-ELISA. RT-PCR was conducted on the ELISA-positive samples using specific primers of beet poleroviruses. The primer used to amplify ORF3 (Coat protein gen) of beet poleroviruses was CP+ and CP-. Three sets of primers were used to amplify ORF0 of beet poleroviruses consisting of MpxBM+ and MpxBM-, MpxBW+ and MpxBW- and MpxBC+ and MpxBC- for specific detection of BMYV, BWYV and BChV, respectively. Expected sizes of 563 bp and 441 bp were amplified using CP+ and CP- and MpxBM+ and MpxBM- primers, respectively. These specific amplifications represent presence of BMYV in infected sugar beet samples. The PCR products of an isolate named BMYV-Lav were cloned and sequenced. Multiple alignment of deduced amino acid sequence of ORF0 gene of BMYV-Lav and those of other poleroviruses infecting beet and rape revealed the highest similarity with BMYV-1 isolate (98%), whereas analysis of amino acid CP gene showed the highest similarity with a BWYV isolate (97.9% with Brassica yellow virus-GB). In phylogenetic analysis based on amino acid sequence of ORF0 gene (a gene at 5' end of genome), BMYV-Lav was placed in BMYV isolates group, whereas alignment of Coat protein (CP) gene (a gene at 3' end of genome) of BMYV-Lav showed that BMYV-Lav isolate was closer to BWYV isolates than BMYV isolates. These results suggested taking place of recombination in BMYV-Lav.
