183
September 1977
Family: Unallocated ssRNA- viruses
Genus: Unassigned ssRNA- virus
Species: Orchid fleck virus
Acronym: OFV


Orchid fleck virus

Y. Doi
Laboratory of Plant Pathology, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, Japan

M. U. Chang
Laboratory of Plant Pathology, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, Japan

K. Yora
Laboratory of Plant Pathology, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, Japan

Contents

Introduction
Main Diseases
Geographical Distribution
Host Range and Symptomatology
Strains
Transmission by Vectors
Transmission through Seed
Transmission by Grafting
Transmission by Dodder
Serology
Nucleic Acid Hybridization
Relationships
Stability in Sap
Purification
Properties of Particles
Particle Structure
Particle Composition
Properties of Infective Nucleic Acid
Molecular Structure
Genome Properties
Satellites
Relations with Cells and Tissues
Ecology and Control
Notes
References
Acknowledgements
Figures

Introduction

Described by Doi et al. (1969) and Chang et al. (1973).

Selected synonyms

Dendrobium virus (Rev. appl. Mycol. 50: 2989)
Phalaenopsis virus (Rev. appl. Mycol. 51: 426)

A virus with non-enveloped, bacilliform particles about 40 x 150 nm in dip preparations and partially purified preparations, but 32-35 x 100-140 nm in thin sections. It is sap-transmissible to several species of orchids and a few dicotyledonous plants, but with difficulty.

Main Diseases

Causes chlorotic or necrotic flecks in species of Cymbidium, Dendrobium, Oncidium and many other kinds of orchids (Fig.1, Fig.2).

Geographical Distribution

Japan; probably also in West Germany (Lesemann & Doraiswamy, 1975) and Brazil (Kitajima et al., 1974).

Host Range and Symptomatology

Found naturally in a wide range of orchid species, and transmitted experimentally to species in the Chenopodiaceae, Solanaceae and Aizoaceae. A morphologically similar virus occurs in coffee and citrus (see Relationships). Sap-inoculation is difficult, but successful when the temperature is higher than 30°C.

Diagnostic species

Dendrobium nobile, Cymbidium alexanderi, and other orchid species. Chlorotic or necrotic spots, sometimes flecks, first on inoculated leaves, and later on upper leaves. Incubation period is 3-4 weeks. (Fig.1, Fig.2).

Nicotiana glutinosa, N. tabacum cv. Bright Yellow, White Burley, Xanthi-nc and KY-57 (tobacco). Chlorotic or necrotic local lesions after 2-3 weeks. No systemic symptoms (Fig.3, Fig.4).

Propagation species

Cymbidium spp. (e.g. C. alexanderi) are suitable for maintaining cultures, and are good sources of virus for purification.

Assay species

N. tabacum and N. glutinosa can be used for local lesion assays.

Strains

None reported.

Transmission by Vectors

The vector is not known. Attempts to transmit by using an aphid (Myzus persicae) and a mealybug (Diaspis boisduvallii) were unsuccessful (M. U. Chang, unpublished data).

Transmission through Seed

None reported.

Serology

No information.

Relationships

The bacilliform or bullet-shaped particles of orchid fleck virus superficially resemble those of plant rhabdoviruses, but they are smaller, lack an outer envelope, and are still infective after treatment with detergents (e.g. Triton X-100). Their fine structure is similar to that of the internal component of rhabdoviruses, but they are more labile than particles of rhabdoviruses. In particle morphology and intracellular effects, orchid fleck virus closely resembles Dendrobium virus (Petzold, 1971), Phalaenopsis virus (Lesemann & Begtrup, 1971), coffee ringspot virus (Kitajima & Costa, 1972) and citrus leprosis virus (Kitajima et al., 1972).

Stability in Sap

Crude Cymbidium leaf sap, diluted up to 10-2 with 0.1 M phosphate buffer pH 7.15, and partially purified preparations are infective after 1 day at 6°C.

Purification

Homogenize diseased orchid leaves at 4°C in 0.1 M phosphate buffer pH 7.0 containing 0.1 M sodium diethyldithiocarbamate, 0.1% L-ascorbic acid, 5% Triton X-100 and 0.5% sodium deoxycholate. Centrifuge the homogenate at 5000 rev/min for 15 min. Centrifuge the supernatant fluid at 30,000 rev/min for 2 h, suspending the pellet in 0.1 M phosphate buffer. Repeat two more cycles of differential centrifugation. Sucrose density gradient centrifugation is used for further purification (Chang et al., 1976).

Properties of Particles

None reported.

Particle Structure

Particles are bacilliform or sometimes bullet-shaped, about 40 x 150 nm in partially purified preparations or in dip preparations pre-fixed in 2% osmium tetroxide before negative staining with phosphotungstate (Fig.6, Fig.7, Fig.8, Fig.10), but 32-35 x 100-140 nm in thin sections (Fig.5). Particles have no envelope and show a helical structure with a pitch of 4.5 nm (Chang et al., 1976).

Particle Composition

None reported.

Relations with Cells and Tissues

In thin sections of virus-infected tissues, virus particles occur in the nuclei and cytoplasm, and inclusions of low electron density (‘viroplasms’) are also observed in the nuclei. A series of electron micrographs suggests that virus particles are formed in and around the viroplasms and later move to the nuclear envelope. Finally the nuclei deform and the nuclear membrane disrupts to release the virus particles enclosed. In the nuclei, virus particles exist in the chromatin area singly or arranged side-by-side (Fig.5), showing crystalline arrays in cross sections. Virus particles are commonly found to attach at one end to the inner nuclear membrane. A number of virus particles surrounded by the inner membrane often show an appearance like a spoked wheel (Fig.9). Some particles appear to associate with or attach to the endoplasmic reticulum. In addition to virus particles, vacuolated or deformed nuclei, swollen or amoeboid chloroplasts, and swollen mitochondria are observed in virus infected cells (Chang et al., 1976).

References

  1. Chang, Arai, Doi & Yora, Ann. Phytopath. Soc. Japan 39: 171, 1973.
  2. Chang, Arai, Doi & Yora, Ann. Phytopath. Soc. Japan 42: 156, 1976.
  3. Doi, Toriyama, Yora & Asuyama, Ann. Phytopath. Soc. Japan 35: 388, 1969.
  4. Kitajima & Costa, Cienciae Cultura 24: 542, 1972.
  5. Kitajima, Müller, Costa & Yuki, Virology 50: 254, 1972.
  6. Kitajima, Blumenschei & Costa, Phytopath. Z. 81: 280, 1974.
  7. Lesemann & Begtrup, Phytopath. Z. 71: 257, 1971.
  8. Lesemann & Doraiswamy, Phytopath. Z. 83: 27, 1975.
  9. Petzold, Phytopath. Z. 70: 45, 1971.


Figure 1

Systemic necrotic flecks on infected Cymbidium leaves.

Figure 2

Systemic necrotic flecks on infected Oncidium leaves.

Figure 3

Local chlorotic-necrotic spots on a leaf of N. glutinosa.

Figure 4

Local chlorotic spots on a leaf of N. tabacum cv. Xanthi-nc.

Figure 5

Viroplasm adjacent to nucleolus in the nucleoplasm (N. glutinosa). Ne: nuclear envelope; nu: nucleolus; v: virus; vp: viroplasm. Bar represents 1 µm.

Figure 6

Bullet-shaped particle. Bar represents 50 nm.

Figure 7

Intact bacilliform particle. Bar represents 50 nm.

Figure 8

Virus particles in negatively stained preparation from infected Cymbidium leaves. Bar represents 100 nm.

Figure 9

Virus particles surrounded by inner nuclear membrane in perinuclear area, forming ‘spoked wheel’ structures. n: nucleus; v: virus. Bar represents 250 nm.

Figure 10

Virus particles in partially purified preparation. Bar represents 100 nm.