Raspberry leaves showing yellow blotch symptoms caused by RLBV

Soft fruit virus research at the James Hutton Institute is part of an integrated soft fruit crop programme that includes research for genetics, breeding and pathology.

The James Hutton Institute is the sole source in the UK for the production of Rubus and Ribes virus-indexed Pre-basic stock entering the EU Certification Scheme. In addition the James Hutton Institute quarantine facility ensures the high-health status of its collections and germplasm; sourced from around the world; for use in research and in the raspberry and blackcurrant breeding programmes. It also conducts pathogen testing on a commercial basis and is now expanding its research into blueberry cropping.

Soft fruit virology involves the study of existing and new virus diseases that impact on each of these important crops.

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 work has enabled us to design virus-specific PCR diagnostic tests that can be used to identify virus infections in the field and also to ensure that plants in our Pre-basic stock and quarantine facilities are and remain virus-free.

Similarly, we have designed and validated (with Alison Dolan) an improved RT-PCR diagnostic test for Blackcurrant reversion virus (BRV), currently the most economically important virus disease of blackcurrants worldwide.

Another virus, Raspberry bushy dwarf virus (RBDV), has been associated with crumbly fruit disorder, where development of the fruit is affected so that each fruit consists of only a few, large irregular drupelets instead of the usual many, small regular drupelets. Such malformed fruit cannot be harvested leading to significant (or even complete) loss of the crop. The mechanistic basis of crumbly fruit is not known although there is certainly a genetic component, sometimes a viral component and perhaps also an environmental component. We have produced infectious clones of RBDV and have studied some of the molecular aspects of RBDV infection. These tools will be very useful to investigate the role of RBDV in crumbly fruit disorder.

An important part of our work is to respond to outbreaks of virus disease in local and national soft fruit crops.

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 recently identified a new virus, Raspberry leaf blotch virus (RLBV), 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 have identified eight genome RNAs, the largest number for any emaravirus so far, and are investigating the roles of these RNAs and their encoded proteins in the virus life-cycle. RLBV has many similarities in molecular structure to the family of bunyaviruses, which cause many important diseases in humans and animals. 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.