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 restricti on endonuclease profiles of double-stranded forms of BCTV DNA present in total DNA extracts. The results suggested that each isolate contain ed 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 previou sly characterized Calif/Logan and CFH strains of BCTV were recovered f rom each of the nursery isolates, and a single clone resembling the Wo rland strain of BCTV also was recovered from one of the nursery isolat es. Detailed restriction endonuclease mapping of cloned BCTV genomes r ecovered from the nursery isolates revealed minor genotypic variabilit y among cloned genomes of the same strain, and partial nucleotide sequ encing of the origin of DNA replication confirmed strain identities as signed on the basis of restriction endonuclease maps. The complete nuc leotide sequence (2,930 nt, GenBank accession U56975) of the Worland s train of BCTV was determined and verified as a third distinct strain w ith an overall nucleotide sequence identity of 79.0 to 80.2% relative to the Calif/Logan and CFH strains of BCTV.