A DAMAGING OUTBREAK OF ARABIS MOSAIC NEPOVIRUS IN BLACK-CURRANT, THE OCCURRENCE OF OTHER NEPOVIRUSES IN RIBES SPECIES, AND THE DEMONSTRATION THAT ALFALFA MOSAIC-VIRUS IS THE CAUSE OF INTERVEINAL WHITE MOSAIC IN BLACK-CURRANT

In a crop of blackcurrant (Ribes nigrum), cv. Baldwin in fire, chlorot ic mottling and ringspot symptoms in leaves on plants and severe crop loss was associated with infection with arabis mosaic nepovirus (ArMV) and the presence in the soil of its nematode vector, Xiphinema divers icaudatum. This is only the second report of ArMV damaging a crop of b lackcurrant. Tomato black ring (TBRV) and raspberry ringspot nepovirus es were detected in single plants of redcurrant (R. rubrum) in England and flowering currant (R. sanguineum) in Scotland respectively; each of these infected plants showed foliar chlorotic line-pattern symptoms . This is the first record of TBRV in redcurrant. A single blackcurran t plant in New Zealand showing symptoms typical of those described for interveinal white mosaic disease, contained alfalfa mosaic virus (AMV ). When AMV particles were purified and concentrated from herbaceous t est plants and mechanically inoculated to young blackcurrant plants, s everal became infected with AMV and most infected plants developed sys temic symptoms typical of the original disease. This provides the stro ngest evidence to date that AMV is the causal agent of interveinal whi te mosaic disease.