Details of DPV and References

DPV NO: 259 July 1982

Family:
Genus:
Species: | Acronym:

Carlavirus group

Renate Koenig Institut für Viruskrankheiten der Pflanzen, Biologische Bundesanstalt für Land- und Forstwirtschaft, 3300 Braunschweig, Germany

Contents

Type Member

Carnation latent virus.

Main Characteristics


Slightly flexuous filaments, normally 610-700 nm long and 12-15 nm in diameter, often appearing curved to one side and sedimenting at 147-176 S. The particles are constructed of c. 1600-2000 subunits of a single protein species (M. Wt normally 3.1-3.4 x 104) arranged as a helix (pitch 3.3-3.45 nm) enclosing the genome which is a single molecule of single-stranded RNA (M. Wt 2.3-3.0 x 106) and constitutes normally 5-7% of the particle weight. The proteins of some carlaviruses can become partially degraded in the assembled particles.


Thermal inactivation point 55-70°C, longevity in sap a few days, dilution end-point usually 10-3-10-4, occasionally up to 10-6. Most carlaviruses have restricted host ranges, but the different viruses occur in a wide range of monocotyledonous and dicotyledonous hosts. Infections in natural hosts are often latent, but sometimes mosaic symptoms are produced. Carlaviruses are transmitted mechanically and usually in the non-persistent manner by aphids. Some are seed-transmitted. Virus particles occur in the cytoplasm singly or more often in large aggregates which are sometimes banded. The carlavirus group has recently been reviewed by Wetter & Milne (1981).

Members

Definitive and possible or poorly characterized members of the group are listed in Table 1. Some of the poorly characterized viruses might be strains of definitive members.

Table 1. Definitive and possible members of the carlavirus groupa

Reported particle length (nm)   
A. Definitive members
Alfalfa latent (ALV; 211); possibly a strain of PSV (Hampton, 1981) 630-651
Cactus 2 (CaV2; Brandes & Wetter, 1963/64) c. 650
Carnation latent (CLV; 61) 650
Chrysanthemum B (CVB; 110) 685
Elderberry carlavirus (ECV; van Lent, Wit & Dijkstra, 1980) 678
Helenium S (HelVS; Kuschki et al., 1978) 640
Hop latent (HopLV; Probasco & Skotland, 1978) 610
Hop mosaic (HopMV; 241) 650
Lilac mottle (LcMV; Waterworth, 1972) 575-610
Lily symptomless (LiSV; 96) 640
Lonicera latent (LonLV; van der Meer, Maat & Vink, 1980) (=honeysuckle latent? Brunt, Phillips & Thomas, 1980) 656
Mulberry latent (MuLV; Tsuchizaki, 1976) c. 700
Muskmelon vein necrosis (MmVNV; Freitag & Milne, 1970) 674
Narcissus latent (NaLV; 170; Brunt, 1977) 650
Nerine latent (NeLV; Maat et al., 1978) (= hippeastrum latent?) 664
Passiflora latent (PasLV; Brandes & Wetter, 1963/64) 650
Pea streak (PSV; 112) 620-630
Pepino latent (PepLV; Thomas, Mohamed & Fry, 1980) 660-680
Poplar mosaic (PopMV; 75) 675
Potato M (PVM; 87) 650
Potato S (PVS; 60) 650
Red clover vein mosaic (RCVMV; 22) 645
Shallot latent (ShLV; 250) 651
B. Possible or poorly characterized members
Artichoke latent (ArLV; Majorana & Rana, 1970) 673
Caper vein banding (CapVBV; Majorana, 1970) 678
Cassia mild mosaic (CasMMV; Lin et al., 1979) 640
Chicory blotch (ChiBV; Brcák & Cech, 1962) 657
Cole latent (CoLV; Kitajima, Camargo & Costa, 1970) 650
Cowpea mild mottle (CpMMV; 140)b 650
Cynodon mosaic (CynMV; Bhargava, Joshi & Rishi, 1971) 509-632
Daphne S (DaVS; Milne & Forster, 1976) 716
Dulcamara carlavirus A (DuCVA; Lesemann, Weidemann & Bartels, 1971) 663
Dulcamara carlavirus B (DuCVB; Lesemann et al., 1971) 676
Eggplant mild mottle (EMMV; Khalil, Nelson & Wheeler, 1978) 677-693
Fuchsia latent (FuLV; Johns, Stace-Smith & Kadota, 1980) 650
Garlic mosaic (GaMV; Cadilhac et al., 1976) 610-640
Gentiana carlavirus (GeCV; D.-E. Lesemann & R. Koenig, unpubl. data) c. 650
Groundnut crinkle (GrCV; Dubern & Dollet, l981)b 650
Gynura latent (GyLV; Gumpf, Osman & Weathers, 1977) (= strain of CVB?) 680
Helleborus carlavirus (HeCV; Koenig & Lesemann, 1978) 665
Kalanchoe carlavirus (KaCV; Koenig & Lesemann, 1978; Hearon, 1981) 600-650
Nasturtium mosaic (NasMV; da Graça & Martin, 1977) 650-710
Plantain 8 (PlV8; Hammond, 1980)
Voandzeia mosaic (VoMV; Monsarrat, Fauquet & Thouvenel, 1981)b 612
White bryony mosaic (WBMV; Tomlinson & Walker, 1972) 650

a Acronym and Description number or other reference given in parentheses.

b According to A. A. Brunt (pers. comm.) the white-fly transmitted CpMMV and the serologically related VoMV and GrCV possibly form a separate virus group or a subgroup of the carlavirus group. The reported serological relationship between CpMMV and CLV has not been confirmed. Recently, however, GrCV has been reported to be serologically closely related to CLV, PasLV and PVS (Dubern & Dollet, 1981).

Geographical Distribution

Most carlaviruses are found wherever their hosts are grown, some are restricted to certain parts of the world, e.g. PSV (USA).

Transmission by Vectors

Usually transmitted in the non-persistent manner by aphids. With some viruses the frequency of transmission is low (e.g. some isolates of PSV, PVS and PVM), with others no aphid vectors have been identified so far (PopMV, MuLV). The whitefly-transmitted CpMMV may not be a carlavirus (see footnote b to Table 1).

Ecology and Control

Carlaviruses are spread by mechanical contact, by horticultural and agricultural equipment and with varying efficiency by aphids. The vegetative propagation of many of the natural hosts aids their dissemination over long distances. Seed transmission may occur with some legume carlaviruses, but is not common. Transmission by root grafts has been considered for PopMV. Overwintering in weeds is important for RCVMV and PSV. Carlaviruses that cause latent infections often have escaped detection in procedures for screening 'healthy' planting material over long periods of time. The older cultivars of many susceptible crops may therefore be 100% infected. Under natural conditions carlaviruses often occur jointly with potyviruses, probably because their mode of transmission is the same.

Relations with Cells and Tissues

Carlavirus particles occur in the cytoplasm of infected cells, either scattered (especially in immature cells (Tu & Hiruki, 1970; Brunt, Stace-Smith & Leung, 1976) and in sieve tubes (Tu & Hiruki, 1970)) or more frequently in a more or less parallel arrangement in bundle-shaped aggregates which are not surrounded by a membrane. In well preserved tissues these aggregates often appear banded (Edwardson & Christie, 1978), the width of each band corresponding to one particle length (Bos & Rubio-Huertos, 1971; 1972; Christie & Edwardson, 1977). Bundles occur singly or in groups. Often they are associated with the tonoplast membrane, the cell wall or sometimes the chloroplast membrane (de Bokx & Waterreus, 1971; Bos & Rubio-Huertos, 1971; 1972; Rubio-Huertos & Bos, 1973; Brunt et al., 1976; Kuschki et al., 1978).

Cytoplasmic inclusions containing large masses of endoplasmic reticulum interspersed with ribosomes and often unaggregated virus particles are found with several carlaviruses (reviewed by Edwardson & Christie, 1978; see also Kuschki et al., 1978). Cytoplasmic crystalline inclusions consisting of protein and RNA and containing densely aggregated spherical granules are typical of infections with many RCVMV strains (Rubio-Huertos & Bos, 1973).

Properties of Particles

Carlavirus particles are slightly flexuous filaments which often appear curved to one side. Their modal length is usually 610 to 700 nm and their diameter 12-15 nm. Diameters up to 17-18 nm have been reported for LiSV and GyLV. The fine structure of carlaviruses is characterized by files of subunits separated by about four longitudinal furrows. Crossbanding and an axial canal are usually not seen (Varma, Gibbs & Woods, 1968; Wetter & Milne, 1981; Hamilton et al., 1981).


The u.v. absorbance spectra of carlaviruses are typical of nucleoproteins, with maxima at 258 to 260 nm, minima at 243 to 248 nm and Amax/Amin ratios of 1.1 to 1.2. The A260/A280 ratios of 1.1 to 1.3 indicate a nucleic acid content of 5-7%. The absorption coefficient A260(0.1%; 1 cm) which has been calculated for only a few carlaviruses, ranges from 2.1 to 2.8. Particles sediment at 147 to 176 S, and have a buoyant density in CsCl of 1.31 to 1.33 g/cm³.


Carlaviruses have a single coat protein (M. Wt 3.1-3.4 x 104). Increasing amounts of lower M. Wt material may be found in stored virus preparations or in fresh ones in which the virus was exposed to prolonged contact with crude plant sap during the purification procedure. The protein subunits form a primary helix with a pitch of 3.3-3.45 nm. The reported number of subunits per turn of the helix is 10 for RCMV and 12 for CLV (Varma et al., 1968). A particle weight of c. 50-60 x 106, estimated from data for nucleic acid and protein contents and M. Wt, indicates that each particle contains c. 1600 to 1800 protein subunits. A slightly higher estimate of c. 1700 to 2500 is obtained from data for modal length, basic pitch of the helix and number of subunits per turn of the helix.

Genome Properties

Carlavirus particles usually contain 5-7% of single-stranded infective RNA (M. Wt 2.3-3.0 x 106). The base composition (G31; A24; C23; U22) is known only for RCVMV RNA (Varma, Gibbs & Woods, 1970).

Replication

No information.

Relationships

Serological relationships among carlaviruses range from close to distant or not detectable. Positive and negative results of serological cross-tests are summarized in Fig. 1.

Affinities with Other Groups

No close affinities of carlaviruses with viruses in other groups are known. An antiserum to potato virus X has been reported to react with NeLV (Maat, Huttinga & Hakkaart, 1978).

Acknowledgements

The author’s work on carlaviruses was supported by the Deutsche Forschungsgemeinschaft.

Figures

dpv figure

Serological relationships in the carlavirus group. Numbers refer to the references listed below. Blank squares indicate that no results of serological tests have been published. Red numbers (on pink background) indicate that serological tests gave positive results at least with some antisera. Grey numbers (on pale blue background) indicate that tests gave negative results. Further tests with different antisera may nevertheless give positive results as was found with other distantly related viruses.

REFERENCES: (1) Brunt, 1977; (2) Brandes & Wetter, 1963/64; (3) Varma et al., 1970; (4) Hakkaart et al., 1962; (5) van Lent et al., 1980; (6) Kuschki et al., 1978; (7) Adams & Barbara, 1980; (8) Brunt et al., 1980; (9) van der Meer et al., 1980; (10) Waterworth, 1972; (11) Desc. 96; (12) Tsuchizaki, 1976; (13) Maat et al., 1978; (14) Thomas et al., 1980; (15) Berg, 1964; (16) Probasco & Skotland, 1978; (17) Bos et al., 1978; (18) Bos et al., 1972; (19) Freitag & Milne, 1970; (20) R. Koenig, unpublished data.

References list for DPV: Carlavirus group (259)

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