First report of Blueberry scorch virus in Europe

Highbush blueberry (Vaccinium corymbosum) has been planted in various areas of northern Italy for the last thirty years, in an effort to actively maintain cropped hillside and mountainside areas with acidic soil. The crop has gained also some economic importance for the fresh fruit market.

During the summer of 2004, a number of plants from a blueberry crop field in southern Piedmont (Costigliole Saluzzo, Cuneo Province) showed symptoms generally associated with blueberry scorch disease (Martin & Bristow, 1988) (Fig.1). Towards the end of the season, 23 leaf samples were collected from various plants showing symptoms of different cultivars: Blueray, Berkeley and Bluecrop. Leaf extracts were examined by electron microscopy using negatively stained preparations. A filamentous virus with longitudinal ribbing typical of the carlaviruses was found in some samples. Specific ELISA testing was then carried out, according to the manufacturer's instruction (Agdia, USA), for a number of viruses often found in blueberry crops. Thirteen of the collected samples tested positive for Blueberry scorch virus (BlScV), whereas none tested positive for Blueberry shock virus (BlShV) and Blueberry leaf mottle virus (BLMoV). Four samples containing carlavirus particles were mechanically inoculated onto a range of herbaceous test plants. These did not show any symptoms, as expected from previous experience with BlScV, which was shown to be not mechanically transmissible to a range of herbaceous test plants (Martin & Bristow, 1988).

The virus was then partially purified according to previous protocols (Martin & Bristow, 1988), using leaves taken from BlScV ELISA-positive plants. RNA was extracted from the purified virus and RT-PCR was carried out (Invitrogen); using random hexamers for reverse transcription and the oligonucleotides 5'-GAAAGAAGCACCGGCTCAATc-3' and 5'-GGAGATCTTGGCCATTTGCTC- 3' for PCR. The resulting amplification product of ca. 380 bp was cloned using pGEM-T vector (Promega) and sequenced. The resulting nucleotide sequence of the insert was deposited in Genebank (Accession N° AY823507). A pairwise amino acid sequence comparison, using the amino-terminal region of the coat protein of BlScV isolates so far sequenced, showed that the Italian isolate has the highest identity (70%) to the NJ1 strain of BlScV (Cavileer et al., 1994).

To our knowledge this is the first report of this potentially damaging virus outside of North America.