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IT-BASED DIAGNOSTICS:
POTEXVIRUSES, POTYVIRUSES AND TOBAMOVIRUSES OF ORCHIDS IN AUSTRALIA
Cultivated orchids are often virus infected, perhaps because they are grown intensively. Viruses cause
leaf symptoms such as chlorotic streaking and mosaics, necrotic spots and line patterns and distortion. Flowers may have colour breaking (altered pigmentation), distorted or necrotic areas, and flowerbuds may fail to open properly. Particular viruses may cause no symptoms in some species, and yet severely affect others. Planning control strategies requires viruses to be identified properly as different viruses spread in different ways.
Records of virus infections in cultivated orchids include cymbidium mosaic potexvirus (CymMV),odontoglossum ringspot virus (ORSV) and many potyviruses, only a few of which have been characterised. Potexviruses, potyviruses and tobamoviruses comprise more than a third of the recorded plant virus species, and include many that are agronomically important.
Specific pairs of redundant primers have been designed to conserved regions in each of the potexvirus (genus), potyvirus (family) and tobamovirus (genus) genomes. When used in the sensitive molecular technique of RT (Reverse Transcription)-PCR (Polymerase Chain Reaction) a specific fragment is amplified corresponding to the
region of the viral genome between the primers.
Subsequent gene sequencing of this fragment is then used to accurately characterise the virus to the species
level. Using these techniques we have tested orchids showing symptoms of virus infection from several col-
lections in Australia and confirmed the presence of two viruses that can easily be detected by traditional
methods (electron microscopy and serology); CymMV seems to be common in large collections and ORSV to
a lesser extent.
A previously-undescribed virus, ceratobium mosaic potyvirus (CerMV), was found to be common in several genera in four orchid collections in Australia, and is probably endemic to Australian native populations of the ceratobium group of orchids.
Comparisons with sequences in the international databases showed CerMV to be from the bean common mosaic subgroup of potyviruses and to be clearly distinct from dendrobium mosaic potyvirus and vanilla necrosis potyvirus.(references)
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Anne M Mackenzie, Maureen Nolan,
Ke-Jun Wei
Research School of Biological Sciences
Australian National University
PO Box 475, ACT,2601, Australia
Mark A, Clements
Centre for Plant Biodiversity Research
PO Box 1600, ACT, 2601, Australia
Don Gowanlock
University of Queensland, Brisbane, Australia
Ben J. Wallace
Australian National Botanic Gardens, Canberra, Australia
Adrian J. Gibbs
Research School of Biological Sciences
Australian National University
PO Box 475, ACT,2601, Australia
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