The first report of Broad bean wilt virus 2 in the UK: findings in foxglove and salvia

In 2002, foxglove (Digitalis spp. var. 'Saltwood Summer') plants were received at CSL, with virus-like mottle symptoms. Following mechanical inoculation onto a range of indicator plants, symptoms were observed that included systemic chlorosis and distortion on Chenopodium quinoa and systemic mottle, necrosis and distortion on Nicotiana benthamiana, N. occidentalis P1 and N. hesperis. These indicators were examined by electron microscopy and isometric particles were observed. Both the original samples and indicators showing symptoms were tested by ELISA using a range of antisera (18 in total) specific for viruses with isometric particles, including common ornamental viruses and those recorded as infecting the Scrophulariaceae (including Broad bean wilt virus 1; BBWV-1). All these tests were negative.

In 2005, a range of virus diagnostic microarrays were developed at CSL (unpublished data). As part of the validation process for these, the unknown foxglove virus was tested. Total RNA was extracted from infected C. quinoa, labelled and hybridised onto an array spotted with oligos specific for different RNA viruses. Using this method Broad bean wilt virus 2 (BBWV-2) was detected (Fig. 1). No other viruses were detected, including BBWV-1. Subsequently a BBWV-2-specific antiserum was acquired (DSMZ, Braunschweig, Germany) and ELISA tests were carried out on both the indicators with symptoms and the original, infected foxglove plants, that had been maintained in the greenhouse. Both tested positive for BBWV-2.

Subsequently BBWV-2 has also been detected in a sample of Salvia officinalis var. 'Icterina'. These plants, sourced from Israel, were showing leaf twisting and distortion. Following mechanical inoculation, symptoms similar to those induced by the foxglove virus, appeared on indicator plants. ELISA testing confirmed the presence of BBWV-2.

Since broad bean wilt virus has only recently been classified as two distinct species (Kobayashi et al., 1999), the earlier literature does not specifically refer to BBWV-1 and -2 (Taylor & Stubbs, 1972). As a result, their specific host and geographical ranges are often unclear. However, detailed analysis of the literature does show that previous UK records (such as those in parsley and nasturtium: Frowd & Tomlinson, 1970; Xu et al., 1988), refer to isolates of BBWV-1. In addition, recent UK findings made by CSL in other ornamentals, were all identified as BBWV-1 (unpublished data). As a result, we believed this to be the first report of BBWV-2 in the UK.