Occurrence and distribution of Raspberry bushy dwarf virus in commercial Rubus plantations in England and Wales

Serological surveys for Raspberry bushy dwarf virus (RBDV) made between 1995 and 1997 and covering ≈ 10% of the commercial farms growing Rubus (red raspberry and hybrid berries) in England and Wales showed that this virus was present on approximately one-quarter of all farms and in approximately one-sixth of all plots tested. RBDV was found in all of the four main raspberry cultivars being grown at that time (Autumn Bliss, Glen Moy, Glen Prosen and Leo), in Loganberry and in Tayberry. Fifteen RBDV genotypes (including two that appeared to be mixed) were identified using RT-PCR/RFLPs, but the majority of genotypes were found only rarely. Of the RBDV isolates tested, two genotypes each comprised 12·5% and another 46·4%. None of the three most common genotypes was associated solely with single Rubus cultivars and vice versa. It is suggested that two separate outbreaks of RBDV are occurring in England and Wales. One outbreak comprises the most frequent genotype combined with one of the moderately frequent genotypes; this outbreak is largely confined to the main growing areas and is either spreading between farms or coming from multiple local sources. Circumstantial evidence suggests that these isolates (and hence this first outbreak) are of the RB pathotype. The second outbreak consists of the other moderately frequent genotype and those genotypes which are less common. These genotypes appear to be more scattered across England and Wales and seem more likely to be coming from local sources and not to be spreading naturally between commercial farms.