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Characterization of a U.S. Isolate of Beet black scorch virus

First and second authors: Sugarbeet and Potato Research Unit, third author: Cereal Crops Research Unit, and fifth author: Animal Metabolism Research Unit, U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS), Fargo, ND 58105; fourth author: Crops Research Laboratory, USDA-ARS, Fort Collins, CO 80526; sixth author: Department of Plant Pathology, North Dakota State University, Fargo 58105; and seventh author: Sugarbeet Production Laboratory, USDA-ARS, Salinas, CA 93905.

The first reported U.S. isolate of Beet black scorch necrovirus (BBSV) was obtained and characterized. Host range of the virus for localized and occasionally systemic infection included the Chenopodiaceae and Tetragonia expansa; Nicotiana benthamiana supported symptomless systemic infection by the virus. The complete nucleotide sequence of the genomic RNA of the virus, designated BBSV-Co, exhibits 93% similarity to the genome of the ‘Ningxia’ isolate of BBSV from China. Amino acid sequence similarity in predicted genes ranged from 95% in the p4 gene to 97% in the p82 and coat protein genes. A potential additional gene exists within the U.S. isolate of BBSV that is absent from Chinese isolates of BBSV due to nucleotide differences between these isolates within the coat protein gene. Coat protein analysis by isoelectric focusing and by mass spectroscopy indicated the presence of phosphorylated residues. Using primer extension analysis of the 5′ end of the genome and site-directed mutants of genomic clones of BBSV-Co from which infectious RNA was produced, the native 5′ end of the BBSV-Co genome was determined to be 5′-GAAACCTAACC…3′, lacking the two terminal adenosine nucleotides in the published sequences of BBSV from China.