Genetic complexity of a beet curly top virus population used to assess sugar beet cultivar response to infection

Four beet curly top virus (BCTV) isolates obtained from two sugar beet evaluation nurseries in Kimberly, ID, were characterized by restriction endonuclease profiles of double-stranded forms of BCTV DNA present in total DNA extracts. The results suggested that each isolate contained a mixture of at least two distinct BCTV genotypes, and analysis of full-length DNA clones verified that each nursery isolate contained at least two BCTV strains. Full-length DNA clones resembling the previously characterized Calif/Logan and CFH strains of BCTV were recovered from each of the nursery isolates, and a single clone resembling the Worland strain of BCTV also was recovered from one of the nursery isolates. Detailed restriction endonuclease mapping of cloned BCTV genomes recovered from the nursery isolates revealed minor genotypic variability among cloned genomes of the same strain, and partial nucleotide sequencing of the origin of DNA replication confirmed strain identities assigned on the basis of restriction endonuclease maps. The complete nucleotide sequence (2,930 nt, GenBank accession U56975) of the Worland strain of BCTV was determined and verified as a third distinct strain with an overall nucleotide sequence identity of 79.0 to 80.2% relative to the Calif/Logan and CFH strains of BCTV.