Virus Infections in Gentiana Species

Gentiana species generally are of little importance to horticulture. This may explain that little attention has been given to virus infections in these ornamentals, so far. However, during the last couple of years the number of samples for virus diagnosis increased. The main symptoms recorded, were growth reduction, necrotic lesions and decline. The virus isolated most frequently was broad bean wilt virus 2, while the related broad bean wilt virus 1 was not detected. Impatiens necrotic spot virus was identified once and one natural infection by the beet ringspot strain of tomato black ring virus was found. In addition, several isolates of bean yellow mosaic virus were identified. INTRODUCTION Species of Gentiana (gentian) originate in several temperate and arctic zones of North America, Asia and Europe, often in high mountain areas. Several of the over 300 Gentiana species are being grown as ornamental garden plants. Amongst these are G. acaulis, G. asclepiadea, G. sino-ornata and G. verna. Some, e.g. G. triflora var japonica ‘Royal Blue’, are also grown as cut flowers. Propagation is by seeds, as well as by cuttings or division for some species. Recently, in vitro propagated hybrid cultivars of G. scabra like ‘Shusui’ originating in Japan have been introduced as pot plants in Europe. However, the marketing of these vegetatively propagated plants increases the risk of spreading non-indigenous viruses. During the last five years an increase was noticed in the number of symptomatic gentian plants that were submitted for diagnosis to the Plant Protection Service (PPS) of the Netherlands and to Biologische Bundesanstalt für Landund Forstwirtschaft (BBA) in Germany. Samples from cultivars of G. scabra were received most frequently. Most plants showed stunting and necrosis. Necrosis varied from necrotic lesions to necrosis of the whole plant. Occasionally also some leaf mottling was observed. Because of the nature of the symptoms several of these plants were initially tested for bacteria and fungi. However, as these tests were negative, tests for viruses were started. This paper reports on the identification of four different viruses in gentian plants. MATERIALS AND METHODS Samples of various species of Gentiana were obtained from growers in Germany, the Netherlands and the United Kingdom. The first step in the identification process was mechanical inoculation onto herbaceous test plants (Verhoeven et al, 1996). Depending on the symptomatology of the inoculated test plants additional methods were employed for further identification, i.e. (immuno-)electron microscopy (IEM/EM), enzyme linked immunosorbent assay (ELISA), reverse transcriptase-polymerase chain reaction (RTPCR) and sequence analysis of cloned viral genome fragments. For EM crude extracts were adsorbed to formvar carbon-coated copper or nickel Proc. 10 IS Virus Diseases Ornamentals