310
December 1986
Family: Potyviridae
Genus: Potyvirus
Species: Iris fulva mosaic virus
Acronym: IFMV


Iris fulva mosaic virus

O. W. Barnett
Clemson University, Clemson, South Carolina 29631, USA

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

Disease described by Travis (1957) and virus partially characterized by Barnett & Alper (1977).

A virus with filamentous particles about 770 nm long occurring naturally only in hybrids derived from Iris fulva. It has a restricted experimental host range and is transmissible by inoculation with sap and by aphids. Found in northeastern and western USA.

Main Diseases

Causes a mild mosaic, sometimes with leaf malformation, of Iris fulva hybrids (Apogon group: beardless, rhizomatous irises) (Travis, 1957; Barnett & Alper, 1977).

Geographical Distribution

Reported from northeastern USA (Barnett & Alper, 1977); also detected in western USA (O. W. Barnett, unpublished data).

Host Range and Symptomatology

The virus occurs naturally only in hybrids of Iris fulva. The only other iridaceous species infected experimentally were I. sibirica and Belamcanda chinensis (Barnett & Alper, 1977). In addition to these monocotyledonous species, Amaranthus caudatus (Amaranthaceae) and Chenopodium quinoa (Chenopodiaceae) can also be infected by inoculation with sap.

Diagnostic species

Amaranthus caudatus, Chenopodium quinoa. Chlorotic local lesions develop occasionally.

Belamcanda chinensis. Few chlorotic local lesions occur but the plants show a chronic systemic mosaic which is usually distinct but may be very mild. Some of the younger leaves may curl downward or twist as a result of necrotic streaks (Fig.1). The capsule is discoloured and malformed.

Iris fulva hybrids. A faint mosaic or yellow streaking occurs on systemically infected leaves which also may twist. Plants are difficult to infect by inoculation with sap.

Iris sibirica. Systemically infected leaves of inoculated seedlings develop long yellow streaks which soon become necrotic (Fig.2). Infected plants usually die soon after necrosis develops.

Propagation and assay species

Belamcanda chinensis, which is readily infected by inoculation with sap, is a good source of inoculum and of virus for purification. It is also useful for whole plant infectivity assays.

Strains

None reported.

Transmission by Vectors

The virus from I. fulva described by Travis (1957) was transmitted in a non-persistent manner by the aphids Myzus persicae, Macrosiphum euphorbiae (= M. solanifolii) and Aphis fabae. The isolate characterized by Barnett & Alper (1977) was not transmitted by M. persicae, M. euphorbiae or A. craccivora but another isolate, closely related serologically, was transmitted by M. persicae.

Transmission through Seed

Not seed-borne in Belamcanda chinensis (Barnett & Alper, 1977).

Serology

A rabbit injected repeatedly over a 10-month period yielded antiserum which had a low titre in microprecipitin tests and contained antibodies to healthy plant material. Virus particles became coated with homologous antibody in immuno-electron microscopy tests (Ball & Brakke, 1968, modified by Langenberg, 1974) and reacted with homologous antiserum in Ouchterlony gel diffusion tests in the presence of 0.5% sodium dodecyl sulphate (Gooding & Bing, 1970). Reactions with the serum in DAS-ELISA were specific after absorption of the conjugate with healthy plant extracts (Lister, 1978).

Nucleic Acid Hybridization

Complementary DNA made to randomly primed nucleic acid (presumed to be RNA) from iris fulva mosaic virus did not hybridize with nucleic acid from iris severe mosaic virus (bearded iris mosaic virus) or from maize dwarf mosaic virus serotypes A or B in direct molecular hybridization tests done at 60°C in low salt (0.18 M NaCl) buffer (O. W. Barnett, unpublished data).

Relationships

The properties of iris fulva mosaic virus place it in the potyvirus group. Barnett & Alper (1977) found that its particles did not become coated with antibody to iris mild mosaic virus (Brunt, 1973; Barnett & Brunt, 1975), bearded iris mosaic virus (Barnett et al., 1971; Barnett & Brunt, 1975) or iris severe mosaic virus (see Brunt, 1973) in immuno-electron microscopy tests. Iris fulva mosaic virus reacted weakly with an antiserum to maize dwarf mosaic virus-B in DAS-ELISA (O. W. Barnett, unpublished data) but not with antiserum to the following other potyviruses: bean yellow mosaic, clover yellow vein, maize dwarf mosaic-A, soybean mosaic, papaya ringspot (type W) or watermelon mosaic-2.

Stability in Sap

In B. chinensis sap the virus was infective for 2 days but not 4 days at 27°C, for 10 min at 50° but not 60°C, and after diluting to 10-4 but not 10-5.

Purification

Barnett & Alper (1977) found that the following method, adapted from the procedures of Huttinga (1973), gave consistent yields of non-aggregated particles of iris fulva mosaic virus. Homogenize each 1 g infected leaves in 3 ml 0.1 M Tris (adjusted to pH 8.9 with thioglycollic acid) and 1.6 ml of a 1:1 mixture of carbon tetrachloride and chloroform, subject the aqueous phase to one or two cycles of differential centrifugation (1.5 h at 44,000 g; 10 min at 5000 g), and further purify the virus by rate zonal sucrose density gradient centrifugation.

Purification method 2 of Reddick & Barnett (1983), which involves the use of polyethylene glycol, Triton X-100, and equilibrium centrifugation in caesium sulphate, also consistently gave high yields of virus.

Properties of Particles

Purified preparations give a single light-scattering band in density gradient centrifugation. On analytical centrifugation the virus sedimented as a single symmetrical peak which broadened late in the run.

Sedimentation coefficient (s°20, w): c. 141 S (of questionable validity because of possible particle breakage).

A260/A280: 1.19; A260(max)/A247(min): 1.17 (both values corrected for light-scattering).

Particle Structure

Particles are slightly flexuous filaments c. 770 nm long (Fig.3). The virus particles are flexuous in the presence of MgCl2 and straight in the presence of EDTA, effects opposite to those reported for other viruses of the potyvirus group (Govier & Woods, 1971). The particles appear swollen when stained with 2% sodium phosphotungstate, pH 7, but not when stained with 2% ammonium molybdate, pH 7, or 1% uranyl acetate, pH 3.

Particle Composition

Nucleic acid: 6% of particle weight (estimated from the A260/A280 ratio). Single nucleic acid component of about 2.9 x 106 daltons (O. W. Barnett, unpublished data).

Protein: Single polypeptide of about 32,000 daltons (O. W. Barnett, unpublished data).

Relations with Cells and Tissues

In sections of infected Belamcanda chinensis, virus particles are abundant in the cytoplasm of mesophyll cells. Occasionally mitochondria are aggregated (Fig.4) with virus particles surrounding them. Cytoplasmic inclusions are present, consisting of both pinwheels and scrolls with laminated aggregates (Fig.5); this places the virus in Edwardson's (1974) subdivision III of the potyvirus group.

Notes

Besides iris fulva mosaic virus, four other, serologically unrelated, potyviruses are found in iris: iris severe mosaic, iris mild mosaic and bean yellow mosaic viruses (Brunt & Phillips, 1980; Derks et al., 1985), and turnip mosaic virus (Inouye & Mitsuhata, 1978). Iris severe mosaic virus was recently shown to be synonymous with bearded iris mosaic virus (Derks & Hollinger, 1986). Iris mild mosaic virus differs from iris fulva mosaic virus in not infecting Belamcanda chinensis; although it infects Chenopodium quinoa locally, it does so with ease throughout the year, whereas iris fulva mosaic virus infects it with difficulty and only in some seasons. Bean yellow mosaic virus infects a number of standard test plant species, e.g. Pisum sativum; turnip mosaic virus infects several species of Cruciferae and Lupinus albus. Iris fulva mosaic virus is more easily confused with bearded iris mosaic isolates of iris severe mosaic virus which, like it, occur in beardless irises and infect B. chinensis, although inducing more severe symptoms. Thus strains of iris severe mosaic virus from Iris spuria induce severe systemic leaf chlorosis from which B. chinensis plants do not recover and usually die; other strains cause local symptoms and severe systemic mosaic followed by partial recovery or symptomless systemic infection. Bearded iris mosaic virus is placed in Edwardson's (1974) subdivision II of the potyvirus group on the basis of the morphology of its cytoplasmic inclusions, whereas iris fulva mosaic virus is placed in subdivision III. A potyvirus from a rhizomatous iris in Italy reacted with antisera to both iris severe mosaic virus (bearded iris mosaic virus) and iris fulva mosaic virus (Lisa, 1980) but the inclusion bodies caused by this virus were like subdivision II cytoplasmic inclusions.

Iris fulva mosaic virus is distantly related to maize dwarf mosaic virus-B and induces similar types of cytoplasmic inclusion but it does not infect maize (Zea mays), nor does maize dwarf mosaic virus-B infect Belamcanda chinensis.

References

  1. Ball & Brakke, Virology 36: 152, 1968.
  2. Barnett & Alper, Phytopathology 67: 448, 1977.
  3. Barnett & Brunt, CMI/AAB Descriptions of Plant Viruses 147, 4 pp., 1975.
  4. Barnett, de Zoeten & Gaard, Phytopathology 61: 926, 1971.
  5. Brunt, CMI/AAB Descriptions of Plant Viruses 116, 4 pp., 1973.
  6. Brunt, Ann. appl. Biol. 87: 355, 1978.
  7. Brunt & Phillips, Acta Hort. 109: 503, 1980.
  8. Derks & Hollinger, Acta Hort. 177: 555, 1986.
  9. Derks, Hollinger & Vink-van den Abeele, Acta Hort. 164: 309, 1985.
  10. Edwardson, Monogr. Ser. Fla agric. Exp. Stn No. 4, 398 pp., 1974.
  11. Gooding & Bing, Phytopathology 60: 1293, 1970.
  12. Govier & Woods, J. gen. Virol. 13: 127, 1971.
  13. Huttinga, Neth. J. Pl. Path. 79: 125, 1973.
  14. Inouye & Mitsuhata, Noguku Kenkyu 57: 1, 1978.
  15. Langenberg, Phytopathology 64: 128, 1974.
  16. Lisa, Acta Hort. 110: 39, 1980.
  17. Lister, Phytopathology 68: 1383, 1978.
  18. Reddick & Barnett, Phytopathology 73: 1506, 1983.
  19. Travis, Phytopathology 47: 454, 1957.


Figure 1

Mosaic symptoms in Belamcanda chinensis. Note that one leaf is twisted as a result of virus infection.

Figure 2

Leaves of Iris sibirica, infected by inoculation with sap, showing long, bright yellow-orange streaks (lighter areas).

Figure 3

Virus particles in 0.1 M Tris buffer with 0.05 M MgCl2 and stained with ammonium molybdate. Bar represents 150 nm.

Figure 4

An aggregate of mitochondria in a thin section of B. chinensis tissue. Virus particles are between the mitochondria. Bar represents 250 nm.

Figure 5

Scrolls and tubes, laminated aggregates, and one partial pinwheel in thin section of B. chinensis leaf tissue. Bar represents 375 nm.