Species: Iris severe mosaic virus
|This is a revised version of DPV 147|
A. A. Brunt
Institute of Horticultural Research, Littlehampton, Sussex, England, BN17 6LP
A. F. L. M. Derks
Bulb Research Centre, 2160 AB Lisse, The Netherlands
O. W. Barnett
Clemson University, Clemson, South Carolina 29634-0377, USA
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
Properties of Infective Nucleic Acid
Relations with Cells and Tissues
Ecology and Control
Disease described in bulbous and rhizomatous irises by Brierley & McWhorter (1934, 1936) and in crocus by Van Slogteren (1956, 1958a). Virus partially characterized by Barnett et al. (1971), Brunt & Phillips (1980) and Derks et al. (1985).
A virus with fiexuous filamentous particles c. 750 nm long, prevalent in bulbous and rhizomatous irises and occasionally present in crocus. It is transmissible in the non-persistent manner by aphids and, less easily, by mechanical inoculation. World-wide distribution.
Belamcanda chinensis. Commonly-occurring isolates of the type strain from rhizomatous iris induce a few spreading necrotic lesions in inoculated leaves after c. 14 days and severe chlorotic mottling in the first few systemically infected leaves (Fig.6), but symptomless infection in leaves produced later; avirulent isolates induce inconspicuous or symptomless systemic infection, but virulent isolates cause conspicuous leaf chlorosis (Fig.7), severe stunting, leaf necrosis and death of infected plants (Brierley & Smith, 1948; Barnett et al., 1971; Travis, 1957; Derks et al., 1985; Derks & Hollinger, 1986).
Crocus vernus. Pale green mosaic patterns, particularly at leaf bases, and dark stripes in the petals (Fig.3) in the year after inoculation.
Rhizomatous irises (Pogon, Apogon, Oncocyclus and Evansia types). Intolerant cultivars show conspicuous chlorotic mosaic on the leaves (Fig.4), and produce short-lived flowers which are often broken or have tear-drop markings (Fig.5); 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.
Cultures can be maintained conveniently in Belamcanda chinensis, Iris x hollandica and Crocus vernus. All three species are also good sources of inoculum and of virus for purification.
No species are sufficiently susceptible for sensitive assays. Iris x hollandica and Belamcanda chinensis, however, can be used for aphid transmission and virus stability tests.
Type strain. In B. chinensis this strain induces a few local necrotic lesions followed initially by conspicuous systemic leaf chlorosis; leaves produced later are often symptomless. Common in bearded Eupogon irises (e.g. Iris pumila and I. ricardi), but also detected in I. gatesii (Oncocyclus iris), I. x hollandica and I. anglica.
Avirulent strain. In B. chinensis this strain induces distinct necrotic or chlorotic stripes and/or ringspots in inoculated leaves, but almost symptomless infection in systemically infected leaves. Isolated from I. x hollandica, and also with difficulty from I. susiana (bearded Oncocyclus iris) and Crocus vernus.
Virulent strain. In B. chinensis, isolates of this strain from I. spuria (beardless iris) induce severe leaf chlorosis (Fig.6) and eventual death of systemically infected leaves. Symptoms in I. spuria and B. chinensis are indistinguishable from those previously attributed to beardless iris mosaic virus (Brierley & Smith, 1948). Virulent strains have also been isolated from I. aurea, I. germanica and I. susiana (Fig.7).
Although iris severe mosaic virus isolates from bearded and bulbous irises are serologically related (Derks & Hollinger, 1986; O. W. Barnett, unpublished data; A. A. Brunt, unpublished data), their RNA molecules showed no sequence homology in reciprocal molecular hybridization tests with cDNA prepared to the nucleic acid of each (O. W. Barnett, unpublished data). The failure to detect hybridization might indicate that bearded iris mosaic virus is not synonymous with iris severe mosaic virus; the hybridization data, however, need to be confirmed because serological and hybridization tests usually give similar information about the relationships between viruses, strains and isolates.
The virus can also be purified from Crocus vernus by clarifying leaf extracts with chloroform before precipitating virus with polyethylene glycol in a procedure similar to that used for purifying lily symptomless virus (Derks & Vink-van den Abeele, 1980); preparations so obtained are relatively free of host contaminants and are thus especially useful for the production of antisera for enzyme-linked immunosorbent assays (A. F. L. M. Derks, unpublished information).
A260/A280: 1.12; A260(max)/A280(min): 1.15 (both values after correction for light-scattering).
Protein: c. 95% of particle weight; one type of polypeptide of M. Wt 33,000 (Alper et al., 1984).
Four potyviruses are known to infect bulbous and rhizomatous irises (Brunt & Phillips, 1980; Derks et al., 1985; Inouye & Mitsuhata, 1978). Unlike iris severe mosaic virus, the other three (bean yellow mosaic, iris mild mosaic and turnip mosaic viruses) are all readily sap-transmitted to dicotyledonous diagnostic hosts; moreover, all three are serologically distinct from iris severe mosaic virus. The latter is also serologically distinct from another potyvirus (iris fulva mosaic virus) infecting rhizomatous irises (Barnett & Alper, 1977). Two other viruses with filamentous particles, narcissus latent carlavirus (Brunt, 1977; Asjes, 1979) and lilac chlorotic leafspot closterovirus (Lisa, 1980), also infect irises but have particles which differ from those of iris severe mosaic virus in length, in serological reactions and in their ability to infect dicotyledonous hosts.
Rhizomatous irises infected with iris severe mosaic virus in Britain also commonly contain
cucumber mosaic cucumovirus
(Brunt, 1968) or, rarely,
broad bean wilt fabavirus
(Bailiss et al., 1975).
Tobacco ringspot nepovirus occurs occasionally in rhizomatous iris in the
USA and Britain
(Travis & Brierley, 1957;
Brunt, 1972) and in bulbous iris in The
Tobacco mosaic tobamovirus and
tobacco rattle tobravirus have also
been reported to occur in bulbous iris in The Netherlands
(Asjes, 1979). Unlike iris severe
mosaic virus, however, these five viruses have isometric or rod-shaped particles, they infect
a wide range of plant species and all can be quickly identified by their serological or other
Iris severe mosaic virus occurs naturally in Crocus vernus and C. flavus; bean yellow mosaic virus, however, occurs in C. flavus and C. sativus but not in C. vernus (Derks et al., 1983; Russo et al., 1979). Bean yellow mosaic and other viruses reported to infect crocus such as tobacco rattle (Van Slogteren, 1958b), arabis mosaic (Asjes, 1974) and cucumber mosaic (A. A. Brunt & S. Phillips, unpublished information) are easily distinguished from iris severe mosaic virus in having extensive natural and experimental host ranges and, with the exception of the serologically distinct bean yellow mosaic virus, in having isometric or rod-shaped particles.
Conspicuous systemic leaf chlorosis in bulbous iris cv. Professor Blaauw.
Flower breaking in bulbous iris cv. Professor Blaauw.
Flower breaking in Crocus vernus cv. Remembrance.
Mosaic leaf symptoms in bearded iris.
Tear drop markings in infected flower of bearded iris.
Severe systemic leaf chlorosis in Belamcanda chinensis induced by virulent strains from Iris spuria.
Severe systemic leaf chlorosis in Belamcanda chinensis induced by virulent strains from Iris susiana.
Virus particles mounted in potassium phosphotungstate. Bar represents 250 nm.
Membrane-bound aggregate of virus particles. Bar represents 500 nm.
Section of Belamcanda chinensis leaf showing pinwheels and laminated aggregates. Bar represents 500 nm.