![]() ![]() In the current study, the BNYVV strains isolated from different provinces of Turkey with long history of sugar beet cultivation have been subjected to comprehensive genomic analyses of all the RNA components and further phylogenetic studies were carried out. With more than 340 thousand hectares of sugar beet harvesting area, Turkey is the world’s fifth largest sugar beet producing country (FAO stat, 2017) and rhizomania is known to cause serious economic losses in sugar beet production 26. Studies also revealed that the J-type East Asian BNYVV isolates was different from French isolates for the length and the sequence of RNA-5 7, 25. However, RNA-5 species was previously described in East Asian isolates 20. Type P is associated with RNA-5 and was first isolated from the city of Pithiviers, France 24. Type A is found in European countries as well as in the USA, China, and Japan, whereas, Type B occurs mainly in countries such as France, Germany, Sweden, Poland, China and Iran 6, 10, 22, 23. ![]() A and B are the most widespread types such that A-type is more prevalent than B-type virus and the P is a rare type throughout the world 3. BNYVV is mainly divided into three pathogenic types designated as A, B and P types 4, 8, 12, 17. Moreover, the interaction between RNA-3, RNA-4 and RNA-5 increases rhizomania symptoms 11, 20. Comparative studies revealed that the RNA-1, RNA-4, and RNA-5 contribute to the development of different rhizomania symptoms 7. ![]() RNA-5 (1342–1347 nt in length) is associated with rhizomania severity, but is not required for virus survival 20, 21. RNA-4 (1431 nt) plays a key role in transmission of the virus by P. RNA-3 consisting of a 1775 nt-long RNA species, is involved in viral pathogenicity 7, 10, 11, 17, 18. Therefore, when the virus vector Polymyxa betae Keskin 15 is not present, RNA-1 and RNA-2 are required for the maintenance of BNYVV in the environment 8, 14, 16. RNA-1 and RNA-2, which contain 67 nt-long RNA species, respectively, encode viral “housekeeping” genes involved in virus replication, assembly, cell-to-cell movement and suppression of post transcriptional gene silencing 13, 14. In addition, a fifth RNA species (RNA-5) has been identified in some of the European and Asian BNYVV isolates 6, 7, 8, 9, 10, 11, 12. The BNYVV genome is multipartite and composed of four single-stranded RNA species designated as RNA-1, RNA-2, RNA-3, and RNA-4, coating with a 21-kDa protein 5. This disease reduces sugar content by 8%, root yield up to 90%, and sugar yield up to 80% 3, 4. Tamada and Baba 2 first identified Beet necrotic yellow vein virus (BNYVV) as the cause of rhizomania when they isolated the virus from infected plants of sugar beet fields in Japan. Since the first report of rhizomania 1 numerous studies have reported the worldwide infection of sugar beet fields with this disease. Rhizomania is one of the most destructive soil-borne diseases of sugar beet ( Beta vulgaris L.) worldwide. We anticipate that these findings will be useful for future genetic characterization and evolutionary studies of BNYVV, as well as for developing sustainable strategies for the control of this destructive disease. The creation of new variants of the virus emphasizes the necessity to develop new generation of resistant crops. The RNA-5 factor which enhance the pathogenicity, is rarely found in the isolates studied (20%). Furthermore, RNA-1 and RNA-4 are either derived from A, B, and P-types or a mixture of them. Our findings indicate that the isolates harbor European A-type RNA-2 and RNA-3, nevertheless, RNA-5 is closely related to East Asian J-type. Here, we report the occurrence of genetic reassortment and emergence of new variants of BNYVV among the isolates of Thrace and Asia Minor (modern-day Turkey). However, over time, viruses undergo genetic alterations and develop new variants to break crop resistance. Resistance to rhizomania has been conferred to sugar beet varieties by conventional breeding methods or modern genome engineering tools. Understanding genome composition of the virus not only determines the degree of pathogenicity but also is required to development of resistant varieties of sugar beet. The multipartite genome of the BNYVV contains four or five single-stranded RNA that has been used to characterize the virus. Beet necrotic yellow vein virus (BNYVV) is the cause of rhizomania, an important disease of sugar beet around the world. ![]()
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