Beet necrotic yellow vein virus (BnYVV) is the cause of rhizomania, an important disease of sugar beetaround the world. The multipartite genome of the BNYVV contains four or five single-stranded RNA that has been used to characterize the virus. 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. Resistance to rhizomania has been conferred to sugar beet varieties by conventional breeding methods or modern genome engineering tools. However, over time, viruses undergo genetic alterations and develop new variants to break crop resistance. 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). 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. Furthermore, RNA-1 and RNA-4 are either derived from A, B, and P-types or a mixture of them. The RNA-5 factor which enhance the pathogenicity, is rarely found in the isolates studied (20%). The creation of new variants of the virus emphasizes the necessity to develop new generation of resistant crops. 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.Rhizomania is one of the most destructive soil-borne diseases of sugar beet (Beta vulgaris L.) worldwide. Since the first report of rhizomania 1 numerous studies have reported the worldwide infection of sugar beet fields with this disease. 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. This disease reduces sugar content by 8%, root yield up to 90%, and sugar yield up to 80% 3,4 . 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 . In addition, a fifth RNA species (RNA-5) has been identified in some of the European and Asian BNYVV isolates 6-12 . RNA-1 and RNA-2, which contain 6746 and 4612 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 . 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-3 consisting of a 1775 nt-long RNA species, is involved in viral pathogenicity 7,10,11,17,18 . RNA-4 (1431 nt) plays a key role in transmission of the virus by P. betae 7,11,13,19 . RNA-5 (1342-1347 nt in length) is associated with rhizomania severity, but is not required for virus survival 20,21 . Comparative studies revealed that the RNA-1, RNA-4, and RNA-5 contribute to the development ...
