DETECTION AND MOLECULAR CHARACTERIZATION OF THE CAUSAL AGENT OF BLACKCURRANT REVERSION DISEASE
P SUSI1,2, S LATVALA1, A LEMMETTY3, SHIRVONEN1, K VALIMAKI1 and K LEHTO1
1Department of Biology, Laboratory of Plant Physiology and Molecular Biology, 20014 University of Turku; 2Department of Plant Production, 00014 University of Helsinki, Finland; 3Agricultural Research Centre, Institute of Plant Protection, 31600 Jokioinen, Finland
Background and objectives
At least two forms of the disease are known. The severe form (R), occurring mostly in Eastern Europe and Scandinavia, causes distinct leaf malformations. The leaves of infected plants are narrower, and have a decreased number of main veins, larger but fewer marginal serrations and a basal sinus that is less lobed. In addition, the plants affected with the severe form occasionally develop strong malformations of the flowers, including the absence of stamens, elongation of the style and an increase in the number of petals, and some blackcurrant cultivars also show strong proliferation of shoots. Symptoms caused by the less-severe, or common form (E) of the disease are much less pronounced than the symptoms of the R-form. The type and intensity of symptoms vary between blackcurrant cultivars, and the symptoms of the E-form of reversion may be easily overlooked due to the normal variation in blackcurrant leaf shapes. Recognition of the disease based on field symptoms is therefore unreliable.
Results and conclusions
Using an IC-RT-PCR detection method, the virus has been detected in numerous samples of reverted blackcurrant obtained from many geographic locations, and from samples of gall mite vectors . The isolated virus has been mechanically inoculated back to healthy blackcurrant plants, in which the acute symptoms of reversion were subsequently produced, and the virus was detected by IC-RT-PCR. These data prove that the isolated virus is the causal agent of the reversion disease, and therefore the virus is called the blackcurrant reversion virus (BRV). Pathogen-derived resistance to reversion disease is currently being tested in transgenic tobacco plants expressing the coat-protein gene of BRV in different orientations. The tested viral sequences will eventually be transformed to blackcurrant for production of reversion-resistant blackcurrant cultivars.