White Phalaenopsis Ringspots
1
Carlye Baker, David Davison and Carol Scoates 2
I
NTRODUCTION: Since 2000, orchid growers have sent
white Phalaenopsis spp. orchids with necrotic/chlorotic
target spot symptoms (Fig. 1) to the Division of Plant
Industry (DPI). The samples always arrived during
the late fall and early winter. Although it was suspected that
these plants were infected with a virus, all serological tests for
known orchid viruses were negative. The cause of these partic-
ular symptoms on white Phalaenopsis orchids has remained a
mystery until 2007. Samples from two different nurseries have
tested positive for two tospovirus species. One sample tested
positive for Tomato spotted wilt virus (TSWV) and another
tested positive for Impatiens necrotic spot virus (INSV).
PATHOGEN: Tospoviruses (Adkins et al. 2005) belong to the
virus family Bunyaviridae, which are primarily animal-infect-
ing viruses. The genus Tospovirus is the only plant-infecting
member of the Bunyaviridae. Fifteen to 18 different species of
ruses do not appear to spread systemically in this orchid host.
Serological tests with non-symptomatic leaves of infected
plants are negative. The lesions, though spectacular on some
plant leaves, appear to be local lesions and the titer of virus is
low and decreases with time. This means that serological test-
ing should be done soon after the appearance of symptoms.
Historically, the symptoms have disappeared during the sum-
mer and then reappeared in the fall to early winter when the
plants were blooming.
CONTROL: The best control of a plant virus is always avoid-
ance of infection. Obtain orchids from clean so urces and grow
orchids away from any host that could harbor these two vi-
ruses or their thrips vectors (Pottorff and Newman 2006). This
would include plants such as chrysanthemums, which are sus-
ceptible to both TSWV and INSV, and impatiens and prayer
plants which are susceptible to INSV. The control of weeds
that could harbor either virus or the thrips vector is also war-
ranted. Any plants with symptoms should be removed or at
least separated from plants without symptoms.
SUMMARY: Although early serological diagnosis is pos-
sible, this appears to be one situation where a viral diagnosis
can be made with symptoms. White Phalaenopsis orchids with
the symptoms shown in Fig.1 apparently have been visited by
thrips carrying one of two tospoviruses, TSWV or INSV.
LITERATURE CITED
Fig. 1. Symptoms of Tospovirus infection in Phalaenopsis.
Photo: Jeffrey Lotz
tospoviruses have been recognized including TSWV and
INSV. TSWV has a large host range (800 plant species) and is
mostly, but not exclusively, a viral disease found in field crops.
INSV has a smaller host range and is mostly a virus found
infecting ornamental greenhouse-grown crops. Both viruses
have been reported in orchids since the early 1990s (Hu et al.
1993, Koike and Mayhew 2001).
VECTOR: Tospoviruses are transmitted from plant to plant
by several species of thrips. The most common species that
vectors these viruses is the western flower thrips (Franklini-
ella occidentalis).
DETECTION AND DIAGNOSIS: The diagnosis of these
viruses in Phalaenopsis orchids has proven difficult. These vi-
Phalaenopsis - Fourth Quarter, Vol. 21(2) 2011
Adkins, S, T. Zitter, and T. Momol. 2005. Tospovirus (Family Bunya-
viridae, Genus Tospovirus), Fact Sheet PP-212. Plant Pathology
Department, Florida Cooperative Extension Services, Institute of
Food and Agriculture Sciences, University of Florida, Gainesville.
http://edis.ifas.ufl.edu/PP134
Hu, J.S., S. Ferrerira, M. Wang and M.Q. Xu. 1992. Detection of Cym-
bidium Mosaic Virus, Odontoglossum Ringspot Virus, Tomato
Spotted Wilt Virus, and Potyviruses Infecting Orchids in Hawaii.
Plant Disease 77: 464-468
Koike, S.T. and D.E. Mayhew. 2001. Impatiens Necrotic Spot Virus
found in Oncidium. Orchids. The Magazine of the American Or-
chid Society 70: 746-747
Pottorff, L.P. and Newman, S.E. 2006. Greenhouse Plant Viruses
(TSWV/INSV). http://www.ext.colostate.edu/pubs/Garden/02947.html
1 Plant Pathology Circular No. 406
2 Carlye Baker ([email protected]), David Davison (davisond@
doacs.state.fl.us) and Carol Scoate: Plant Pathology Section, Florida
Department of Agriculture & Consumer Services — Division of Plant
Industry, P.O. Box 147100, Gainesville, Florida 32608.
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