Details of DPV and References
DPV NO: 147 October 1975
Species: Iris severe mosaic virus | Acronym: ISMV
There is a more recent description of this virus: DPV 338
Bearded iris mosaic virus
O. W. Barnett Clemson University, Clemson, South Carolina, USA
A. A. Brunt Glasshouse Crops Research Institute, Littlehampton, Sussex, England
- Main Diseases
- Geographical Distribution
- Host Range and Symptomatology
- Transmission by Vectors
- Transmission through Seed
- Transmission by Grafting
- Transmission by Dodder
- Nucleic Acid Hybridization
- Stability in Sap
- Properties of Particles
- Particle Structure
- Particle Composition
- Properties of Infective Nucleic Acid
- Molecular Structure
- Genome Properties
- Relations with Cells and Tissues
- Ecology and Control
A virus with filamentous particles c. 12 x 750 nm, prevalent in many species of rhizomatous iris. It is transmissible to iris and one other iridaceous species by sap-inoculation, and by aphids after brief acquisition feeds. A typical but apparently distinct member of the potyvirus group. Distribution probably world-wide.
Causes conspicuous chlorotic markings on the leaves and flower breaking in intolerant cultivars of bearded (Eupogon and Oncocyclus groups), crested (Evansia group) and beardless (Apogon group) rhizomatous iris, but inconspicuous leaf chlorosis or even symptomless infection in other cultivars. Symptoms are usually more severe in plants grown at low temperatures (16°C), or in those also containing cucumber mosaic virus (Brunt, 1968; Brunt, 1975; Barnett, de Zoeten & Gaard, 1971).
Reported from the USA (Brierley & McWhorter, 1936), Japan (Fukushi, 1932) and Europe (Moore, 1949). Distribution probably world-wide, but the identity of the virus concerned in early records is uncertain because, until 1971, mosaic diseases in bulbous and rhizomatous irises were generally assumed to be caused by the same virus (Barnett, de Zoeten & Gaard, 1971).
Host Range and Symptomatology
The virus is only known to occur naturally in rhizomatous irises. It is transmissible by aphids or by sap-inoculation to one of three other iridaceous species (Belamcanda chinensis although not Gladiolus or Freesia spp.), but it infects none of 30 species from 7 dicotyledonous families (Barnett, de Zoeten & Gaard, 1971; Brunt, 1975).
- Belamcanda chinensis.Commonly-occurring isolates of the type strain induce a few spreading necrotic lesions in inoculated leaves after c. 14 days and severe chlorosis in the first few systemically-infected leaves (Fig. 5) but symptomless infection in leaves produced later; avirulent isolates induce inconspicuous or symptomless systemic infection, but virulent isolates cause conspicuous leaf chlorosis, severe stunting, leaf necrosis and death of infected plants (Brierley & Smith, 1948; Barnett, de Zoeten & Gaard, 1971).
- Iris spp. Intolerant cultivars of rhizomatous iris produce conspicuous chlorotic mosaic on the leaves (Fig. 1), and short-lived flowers which are often broken (Fig. 4) or have tear-drop markings (Fig. 7); some tolerant cultivars remain almost symptomless, others have faintly chlorotic leaves but normal flowers. The leaves of I. tectorum (crested iris) often develop chlorotic or water-soaked ringspot and line patterns (Fig. 2).
- Cultures are best maintained in Belamcanda chinensis which is also a good source of inoculum and of virus for purification. This species is especially convenient because it germinates and grows quickly, and seedlings are readily infected.
- Belamcanda chinensis:by recording the proportion of inoculated plants that become infected.
Three strains of bearded iris mosaic virus have been recognized by the
severity of the symptoms they
induce in Belamcanda chinensis (O. W. Barnett, unpublished information).
Type strain. In B. chinensis this strain induces a few local necrotic
initially by conspicuous systemic leaf chlorosis but leaves produced later are often
in bearded Eupogon irises (e.g. Iris pumila, I. ricardi).
Avirulent strain. In B. chinensis this strain induces distinct necrotic or
stripes and/or ringspots in inoculated leaves
but almost symptomless infection in
systemically-infected leaves. Isolated from I. susiana (bearded Oncocyclus iris)
Virulent strain. In B. chinensis, isolates of this strain from I. spuria (beardless iris) induce severe systemic leaf chlorosis (Fig. 6) and death. Symptoms in I. spuria and B. chinensis are indistinguishable from those previously attributed to beardless iris mosaic virus (Brierley & Smith, 1948).
Transmission by Vectors
Transmitted efficiently by some races of the aphids Macrosiphum euphorbiae and Myzus persicae after acquisition feeds of 3-5 min (Brierley & Smith, 1948; Barnett, de Zoeten & Gaard, 1971; O. W. Barnett, unpublished data).
Transmission through Seed
Not seed-borne in Belamcanda chinensis (Barnett, de Zoeten & Gaard, 1971).
Transmission by Dodder
The virus is a good immunogen; antiserum collected 6 weeks after injecting a rabbit intra-muscularly with c. 0.45 mg of virus emulsified in Freunds complete adjuvant reacted in micro-precipitin tests to a homologous titre of 1/2048.
The virus has many properties in common with potyviruses, but is serologically unrelated to similar viruses commonly infecting iridaceous species (iris mild mosaic, iris severe mosaic, I. fulva mosaic, bean yellow mosaic, turnip mosaic, freesia mosaic) and to four other viruses of the same group (Barnett, de Zoeten & Gaard, 1971; Brunt, 1975).
Stability in Sap
In Belamcanda chinensis sap, the thermal inactivation point is 50°C, dilution end-point 10-3, and infectivity is lost at 27°C after 24-36 h (Barnett, de Zoeten & Gaard, 1971).
Yields of c. 5 mg virus/kg of Belamcanda chinensis leaf tissue are obtainable by the following procedure (Barnett, de Zoeten & Gaard, 1971). Homogenize each 1 g infected leaves in 2 ml of extractant at pH 8.9 containing 0.1 M borate buffer, 0.01 M sodium ethylenediamine-tetraacetate and 0.02 M 2-mercaptoethanol. Remove coarse debris, shake the fluid with 0.5 vol chloroform and centrifuge for 10 min at 8000 g. Sediment virus from the aqueous phase by centrifugation for 90-120 min at 100,000 g, and allow pellets to resuspend for 18-24 h in 0.1 M borate buffer at pH 8.9 containing 0.01 M sodium ethylenediamine-tetraacetate. Adjust the solution to pH 4.8 with 0.05 M citric acid, collect pellets by centrifugation and shake gently for 5-6 h in 0.1 M borate buffer at pH 8.9. Purify the virus further by exclusion chromatography in 2% agarose beads and concentrate by ultrafiltration.
Similar or higher yields of mostly unaggregated virus are obtained as described by Huttinga (1973). Homogenize each 1 g infected leaves in 3 ml 0.1 M Tris-thioglycollate buffer (pH 8.9) 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.
Properties of Particles
Sedimentation coefficient (s°20, w): c. 150 S; some
preparations may also contain faster sedimenting virus aggregates
(A. A. Brunt, unpublished information).
A260/A280: 1.12; A260(max)/A248(min): 1.15 (both values after correction for light-scattering).
Particles (Fig. 10) are slightly flexuous filaments mostly c. 750 x 12 nm. Particles mounted in uranyl formate often have a central canal and show the helical arrangement of the protein subunits.
Nucleic acid: 5% of particle weight (estimated spectrophotometrically).
Protein: c. 95% of particle weight; one type of polypeptide of M. Wt 33,000 (A. A. Brunt, unpublished information).
Relations with Cells and Tissues
In ultrathin sections of infected iris leaves and petals, the virus particles are often scattered throughout the cytoplasm, but in Belamcanda chinensis cells they are also sometimes found in membrane-enclosed ovoid masses c. 8 µm in diameter (Fig. 9). Infected cells of Belamcanda chinensis leaves, but not iris petals, also contain inclusions (Fig. 8) seen in sections as pinwheels, bundles and laminated aggregates (Barnett, de Zoeten & Gaard, 1971).
In particle morphology, bearded iris mosaic virus is indistinguishable from iris mild mosaic and iris severe mosaic viruses, which commonly infect bulbous irises, and from Iris fulva mosaic virus, which is reported to infect some species of rhizomatous iris. The two viruses infecting bulbous irises are serologically distinct from bearded iris mosaic virus (Brunt, 1968; Brunt, 1973; Barnett, de Zoeten & Gaard, 1971). Similarly, Iris fulva mosaic virus (Brierley & Smith, 1948; Travis, 1957) is serologically distinct from bearded iris mosaic virus and differs also in infecting Amaranthus caudatus and Chenopodium quinoa, and having cytoplasmic inclusions which can be seen in leaf sections as scrolls and tubes as well as pinwheels, bundles and laminated aggregates (O. W. Barnett, unpublished information).
Recent tests suggest that beardless iris mosaic virus (Brierley & Smith, 1948; Travis, 1957) is a virulent strain of bearded iris mosaic virus (O. W. Barnett, unpublished), but further tests are needed to establish whether the two are synonymous.
Rhizomatous irises infected with bearded iris mosaic virus in Britain commonly also contain cucumber mosaic virus (Brunt, 1968; Barnett, de Zoeten & Gaard, 1971) or, probably rarely, broad bean wilt virus (Bailiss, Brunt & Dale, 1975); tobacco ringspot virus also occurs occasionally in rhizomatous iris in the USA (Travis, 1957; Travis & Brierley, 1957) and Britain (Brunt, 1972). Unlike bearded iris mosaic virus, these three viruses have isometric particles and infect a wide range of plant species; moreover, all three are readily purified and identified by serological tests and by their physico-chemical properties.
Chlorotic ring-and-line patterns induced in inoculated Belamcanda chineosis leaves by the avirulent strain from Iris susiana.
Necrotic local lesions (arrow) and systemic leaf chlorosis in Belamcanda chinensis infected with bearded iris mosaic virus (type strain).
Severe systemic chlorosis in leaf of Belamcanda chinensis infected with the virulent strain from Iris spuria.
Thin section of Belamcanda chinensis leaf showing pinwheels and laminated aggregates. Bar represents 500 nm.
Thin section of Belamcanda chinensis leaf showing a membrane-bound bundle of virus particles. Bar represents 500 nm.
References list for DPV: Bearded iris mosaic virus (147)
- Bailiss, Brunt & Dale, Pl. Path. 24: 60, 1975.
- Barnett, de Zoeten & Gaard, Phytopathology 61: 926, 1971.
- Brierley & McWhorter, J. agric. Res. 53: 621, 1936.
- Brierley & Smith, Phytopathology 38: 574, 1948.
- Brunt, Ann. appl. Biol. 61: 187, 1968.
- Brunt, Rep. Glasshouse Crops Res. Inst. 1971: 116, 1972.
- Brunt, CMI/AAB Descriptions of Plant Viruses 116, 4 pp., 1973.
- Brunt, Acta hort. 47: 45, 1975.
- Fukushi, Trans. Sapporo Nat. Hist. Soc. 12: 130, 1932.
- Huttinga, Neth. J. Pl. Path. 79: 125, 1973.
- Moore, Bull. Minist. Agric. Fish Fd, Lond. 117: 140, 1949.
- Travis, Phytopathology 47: 454, 1957.
- Travis & Brierley, Pl. Dis. Reptr 41: 524, 1957.