DETAILED SOFT fruit virus research at the James Hutton Institute has come up with designer virus-specific diagnostic tests that can be used to identify virus infections in field crops of crops.

Curator of soft fruit germplasm collections at the Institute, Alison Dolan – talking at a recent soft fruit information day in Dundee – said the efforts should ensure that plants in the sector's nuclear stock and quarantine facilities are and will remain virus-free.

JHI's integrated soft fruit crop programme, she said, included research for genetics, breeding and pathology, and added: "In our recent work we have characterised the individual members of a group of diverse viruses – raspberry leaf mottle virus, black raspberry necrosis virus, raspberry vein chlorosis virus – that are common to UK raspberry crops and are transmitted by either the large raspberry aphid, amphorophora idaei, or the small raspberry aphid, aphis idaei.

"This has enabled us to design virus-specific polymerase chain reaction [PCR] diagnostic tests that can be used to identify virus infections in the field and also to ensure that plants in our nuclear stock and quarantine facilities are and remain virus-free.

"Similarly, we have designed and validated an improved RT-PCR diagnostic test for blackcurrant reversion virus, currently the most economically important virus disease of blackcurrants worldwide."

Another virus under scrutiny, raspberry bushy dwarf virus (RBDV), is associated with crumbly fruit disorder, where development of the fruit is affected so that each fruit consists of only a few, large irregular drupelets (the segmented part of the fruit) instead of the usual regular segments.

The economic impact of this can be severe as fruit that is malformed in this way cannot be harvested cleanly, leading to significant, or even complete, loss of the crop.

Studies have produced infectious clones of RBDV allowing a look at some of the molecular aspects of RBDV infection. Researchers hope that this will be useful in investigating the role of RBDV in crumbly fruit disorder, as well as helping developing ways of responding to outbreaks of virus disease in local and national soft fruit crops.

Ms Dolan, who is also principal investigator for the UK spotted wing drosophila monitoring project, concluded: "In recent years a highly symptomatic disease of raspberry has become prevalent in the UK and in Europe, where plants show strong yellowing and distortion of the leaves, combined with necrosis of lateral and apical shoots, and significant yield loss.

"Early work suggested a mite as the causative agent, although spraying with insecticide to reduce mite numbers did not always reduce disease symptoms.

"We have also recently identified a new virus, raspberry leaf blotch virus, that is associated with this disease and is transmitted by the mite. RLBV is a new member of the emaravirus genus of plant viruses, which are enveloped viruses having multiple, negative-strand RNA genome segments.

"We are involved in collaborations with other researchers to examine how infection of plants and animals by these different viruses might involve related mechanisms and processes," she told the audience.