ردیابی ویروس زردی نکروتیک رگ‌برگ چغندرقند و سایر ویروس‌های خاک برد چغندرقند در مزرعه تحقیقاتی مشهد و تعیین برخی خصوصیات مولکولی آن‌ها

Beet necrotic yellow vein virus (BNYVV) has been reported in mixed-infections with Beet black scorch virus (BBSV), Beet soil-borne virus (BSBV), and Beet virus Q (BVQ) sugar beet farms in Iran. Recently, we have observed symptoms of scorching on leaves and signs of rhizomania disease on the roots of some sugar beet cultivars in sugar beet fields. In this study, sugar beets, which had symptoms of bearded root and black scorching of leaves, were collected from a research farm in KANRRC (Mashhad). Total RNA samples were extracted using the RNeasy Mini Kit. To detect the BSBV, BVQ, and BNYVV. We used the molecular technique of Multiplex reverse transcription-polymerase chain reaction (mRT-PCR). However, for the detection of the BBSV single PCR was used. The partial P25 of the RNA-3 segment of BNYVV was amplified by RT-PCR using the PrimeScript ™ Reverse Transcriptase kits and the PrimeSTAR GXL DNA Polymerase and then PCR product cloned in pGEM®-T Easy Vector. The recombinant plasmids were extracted with Kit PrimPrep Plasmid DNA isolation and sequenced. Sequences were analyzed using the Chromas software and then alignment was performed using the MEGAX software .RT-PCR using the specific primers revealed that BNYVV isolates in the region were the A-type strain. The results showed that the four highly variable amino acids motif (aa 67–70 of P25 protein), in the amino acid (aa) sequences of the P25 protein indicated that BNYVV isolates had ACHG, AHHG, and ARHG residues in tetrad position. So that in the aa68 on p25 protein mutations occurred, in which the amino acid cysteine (C) was replaced by histidine (H) and arginine (R). The two tetrads ACHG and AHHG have already been reported from Iran, but ARHG tetrad is reported for the first time from Iran. As a result, this isolates is considered as a variant. In this study, the BBSV virus was detected in mixed-infections with BNYVV. While in this farm, the resistant cultivars carrying the Rz1 and Rz1+Rz2 gene have been cultivated for successive years, break down the resistance and new resistance-breaking (RB) variants have emerged. More research on BNYVV pathogenicity is therefore urgently needed using the additional sources of resistance and alternative disease control methods. On the other, the results showed that the presence of BBSV and BNYVV could exacerbate the symptoms of Rhizomania syndrome while a single infection by BBSV could just cause vascular necrosis in the root and black scorching symptoms on sugar beet leaves. This can be very important in diagnosing a disease based on symptoms and preventing errors in evaluating the resistance of sugar beet cultivars in the field.