Iris fulva mosaic virus
O. W. Barnett
Clemson University, Clemson, South Carolina 29631, USA
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.
Causes a mild mosaic, sometimes with leaf malformation, of Iris fulva
hybrids (Apogon group:
beardless, rhizomatous irises) (Travis, 1957
Barnett & Alper, 1977
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Barnett, unpublished data).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
- 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.
Transmission by Vectors
The virus from I. fulva
was transmitted in a non-persistent
manner by the aphids Myzus persicae, Macrosiphum euphorbiae
(= M. solanifolii
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
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
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
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).
The properties of iris fulva mosaic virus place it in the potyvirus
Barnett & Alper (1977)
found that its particles did not become coated with antibody to
iris mild mosaic virus
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
(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
PurificationBarnett & Alper (1977)
found that the following method,
adapted from the procedures of
, 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
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(max)/A247(min): 1.17 (both values corrected for
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 CompositionNucleic acid:
6% of particle weight (estimated from the
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
subdivision III of the potyvirus
Besides iris fulva mosaic virus, four other, serologically unrelated, potyviruses
in iris: iris severe mosaic
iris mild mosaic
and bean yellow mosaic
(Brunt & Phillips, 1980
Derks et al., 1985
turnip mosaic virus
(Inouye & Mitsuhata, 1978
Iris severe mosaic virus was recently shown to be synonymous with bearded iris mosaic
(Derks & Hollinger, 1986
). Iris mild mosaic virus differs from iris fulva mosaic virus
in not infecting Belamcanda chinensis;
although it infects Chenopodium quinoa
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
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,
inducing more severe symptoms. Thus strains of iris severe mosaic virus from Iris spuria
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
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
) but the inclusion bodies caused by this virus were like subdivision II
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.
- Ball & Brakke, Virology 36: 152, 1968.
- Barnett & Alper, Phytopathology 67: 448, 1977.
- Barnett & Brunt, CMI/AAB Descriptions of Plant Viruses 147, 4 pp., 1975.
- Barnett, de Zoeten & Gaard, Phytopathology 61: 926, 1971.
- Brunt, CMI/AAB Descriptions of Plant Viruses 116, 4 pp., 1973.
- Brunt, Ann. appl. Biol. 87: 355, 1978.
- Brunt & Phillips, Acta Hort. 109: 503, 1980.
- Derks & Hollinger, Acta Hort. 177: 555, 1986.
- Derks, Hollinger & Vink-van den Abeele, Acta Hort. 164: 309, 1985.
- Edwardson, Monogr. Ser. Fla agric. Exp. Stn No. 4, 398 pp., 1974.
- Gooding & Bing, Phytopathology 60: 1293, 1970.
- Govier & Woods, J. gen. Virol. 13: 127, 1971.
- Huttinga, Neth. J. Pl. Path. 79: 125, 1973.
- Inouye & Mitsuhata, Noguku Kenkyu 57: 1, 1978.
- Langenberg, Phytopathology 64: 128, 1974.
- Lisa, Acta Hort. 110: 39, 1980.
- Lister, Phytopathology 68: 1383, 1978.
- Reddick & Barnett, Phytopathology 73: 1506, 1983.
- Travis, Phytopathology 47: 454, 1957.
Mosaic symptoms in Belamcanda chinensis. Note that one leaf is twisted as a result
of virus infection.
Leaves of Iris sibirica, infected by inoculation with sap, showing long, bright
yellow-orange streaks (lighter areas).
Virus particles in 0.1 M Tris buffer with 0.05 M MgCl2 and stained with ammonium
molybdate. Bar represents 150 nm.
An aggregate of mitochondria in a thin section of B. chinensis tissue. Virus
particles are between the mitochondria. Bar represents 250 nm.
Scrolls and tubes, laminated aggregates, and one partial pinwheel in thin section of
B. chinensis leaf tissue. Bar represents 375 nm.