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Molecular Detection and Discrimination of Blueberry red ringspot virus Strains Causing Disease in Cultivated Blueberry and Cranberry

Blueberry red ringspot virus (BRRV) causes red ringspots on the stems, leaves, and ripening fruit of infected highbush blueberry (Vaccinium corymbosum) plants. The disease was originally observed in New Jersey and has now been reported in other blueberry growing regions in the United States, as well as several locations in Europe. A disease with similar symptoms occurs in American cranberry (V. macrocarpon), but BRRV has never been confirmed as the causal agent. Serological detection of BRRV in infected plants has been unsatisfactory. Using a primer set designed for routine detection (RRSV3/RRSV4), we successfully amplified a fragment of the virus from all tissues of infected highbush blueberry plants. Using the same primer set, we confirmed natural infection of BRRV in rabbiteye (V. virgatum) blueberry cultivars and the rabbiteye × V. constablaei hybrid cultivar Little Giant. These species have not been previously reported as hosts for this virus. Viral fragments were cloned from representative blueberry and cranberry plants exhibiting ringspot symptoms. Phylogenetic analysis of sequence data showed that cranberry strains of BRRV are precursors to the more derived blueberry strains. The techniques reported in this paper are being used to evaluate strain variation in Vaccinium species and to identify the as yet unknown vector(s) of this virus.