ISHS Acta Horticulturae 177: IV International Symposium on Flower Bulbs
METHODS OF VIRUS-INDEXING FOR VIRUS-TESTED NARCISSUS STOCKS |
| Author: | W.P. Mowat |
| Abstract:
Up to nine viruses may have the potential to spread in field-grown virus-tested stocks of narcissus in Scotland. Four are transmitted by aphids (narcissus latent, BA3-8 (associated with late season yellows), narcissus yellow stripe and narcissus white streak (putative virus)) and three by nematodes (tomato black ring, raspberry ringspot and tobacco rattle); and the mode of spread of two, narcissus mosaic and narcissus tip necrosis, is unknown. Antisera are available for seven of these viruses. ELISA is already in routine use for indexing stocks for narcissus mosaic and narcissus tip necrosis viruses and is being assessed for detection of the five others. For detecting narcissus tip necrosis and narcissus mosaic viruses, leaf samples from 50 plants can be safely pooled. With the nematode-transmitted viruses, ELISA was more reliable for detecting tomato black ring virus in individual plants than an infectivity assay but was unsatisfactory for tobacco rattle virus because of the antigenic diversity of isolates. Of the two aphid-transmitted viruses, narcissus latent virus was detected when one infected leaf piece was mixed with 24 healthy and BA3-8 virus was detectable when one infected leaf piece was mixed with 9 healthy. However, even in individual samples, BA3-8 antigen is probably not detected reliably until late in the growing season. Results of assessing virus-tested stocks for re-infection promise well for the maintenance of health under the conditions used for propagation. Thus in tests by ELISA no infection with narcissus tip necrosis virus or narcissus mosaic virus were found in VT material released annually since 1976 from nematode- and aphid-proof gauze houses and subsequently propagated in the field. Similarly in tests by ELISA for narcissus mosaic, narcissus tip necrosis, tomato black ring, raspberry ringspot, BA3-8 and narcissus latent viruses, no infections were found in virus-tested narcissus stocks after 6 years of field propagation under the conditions required by the Certification Scheme of the Department of Agriculture & Fisheries for Scotland. Furthermore, visual inspection of the stocks made each year during this period did not reveal any symptoms attributable to infection by tobacco rattle virus or by the aphid-transmitted narcissus yellow stripe virus and narcissus white streak agent(s), and no infection by the soil-borne viruses (tomato black ring, raspberry ringspot and tobacco rattle) was detected by infectivity tests in the first four years of field propagation. | |
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