First record of Bean yellow mosaic virus infecting a member of the orchid genus Dactylorhiza

Dactylorhiza foliosa is a hardy orchid species, native to the Island of Madeira. As a result of large-scale commercial propagation, D. foliosa has recently become more widely available as an unusual, high-value garden plant.

In June 2005, a D. foliosa sample was received at CSL showing symptoms of chlorotic mottle and streaking (Fig. 1). It was part of a large consignment of mature plants, of which 100% showed the same symptom. The sample was tested by ELISA for several viruses which are known to infect orchids including Tomato spotted wilt virus, Impatiens necrotic spot virus, Cymbidium mosaic virus, Odontoglossum ringspot virus and Bean yellow mosaic virus. Of these viruses, the sample tested positive only for Bean yellow mosaic virus (BYMV), using a polyclonal-based DAS-ELISA kit (Loewe Biochemica, Germany). Subsequent examination by transmission electron microscopy revealed the presence of potyvirus-like particles, measuring ca. 750 nm in length. Further confirmation was achieved using RT-PCR with primers designed using BYMV sequences available on Genbank (BYMV F 5’-GGTGAATGGACHATGATGGATGG and BYMV R 5’-CAAGCATGGTGTGCATAT GCATATCACG; CSL, unpublished). A product of the correct predicted size (400 bp) was obtained. Finally the virus was transmitted to two indicator species by mechanical inoculation. Leaf symptoms were observed on Chenopodium quinoa (chlorotic local lesions) and Nicotiana benthamiana (distortion and mosaic). ELISA testing of indicator plants with symptoms confirmed the presence of BYMV.

BYMV is a common disease of legumes and other hosts, found worldwide (Bos, 1970). First identified in Great Britain in the 1930s as ‘pea mosaic’ (Ainsworth, 1940), more recent UK findings include canna lily (Canna indica), broad bean (Vicia faba) and Crocosmia spp. (CSL, unpublished data). It has been reported previously in various orchid species in the USA, Germany and Japan (Lawson & Hsu, 1995) and has been identified recently on several occasions in Masdevallia spp. samples from the UK (CSL, unpublished data). However to our knowledge this is the first ever record of BYMV infecting a member of the genus Dactylorhiza.