129
July 1974
Family: Secoviridae
Genus: Sequivirus
Species: Parsnip yellow fleck virus
Acronym: PYFV

There is a more recent description of this virus: DPV 394

Parsnip yellow fleck virus

A. F. Murant
Scottish Horticultural Research Institute, Invergowrie, Dundee, Scotland

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

Described by Murant & Goold (1968).

An RNA-containing virus which has isometric particles c. 30 nm in diameter. It infects systemically several species of umbelliferous plants, and a few in other families. Transmissible by inoculation of sap, and in a semi-persistent manner by the aphid Cavariella aegopodii. It depends on a helper virus, anthriscus yellows, for transmission by aphids. Occurs in western Europe.

Main Diseases

Causes vein-yellowing, yellow flecks and mosaic symptoms in parsnip (Pastinaca sativa) (Fig.1, Fig.2).

Geographical Distribution

Reported from the UK (Murant & Goold, 1968) and Germany (Wolf & Schmelzer, 1972).

Host Range and Symptomatology

The virus infected systemically 11 of 19 umbelliferous species but only 5 of 25 species from 8 other families. However, a further 15 non-umbelliferous species were infected in inoculated leaves (Murant & Goold, 1968).

Diagnostic hosts

Anthriscus cerefolium (chervil) and Coriandrum sativum (coriander). Local necrotic spots. Young systemically infected leaves blacken and shrivel, at first distally; the necrosis spreads along the petiole into the crown and the plant dies (Fig.3).

Chenopodium amaranticolor. Minute necrotic local lesions; not systemic.

C. quinoa. Local necrotic lesions 2-3 mm in diameter in 4 days (Fig.4), sometimes followed by systemic necrotic flecks and distortion.

Nicotiana clevelandii. Isolates from parsnip and Heracleum sphondylium induce local chlorotic or necrotic spots or rings followed by systemic veinal necrosis; plants later partially recover and show a light and dark green mottle. Plants inoculated with isolates from Anthriscus sylvestris remain symptomless but some may contain a trace of infectivity.

Spinacia oleracea (spinach). Local chlorotic spots, followed by systemic yellow flecks, mottle or leaf-yellowing (Fig.5).

Propagation species

Spinacia oleracea is the best source of virus for purification. This species and Nicotiana clevelandii (except for isolates from Anthriscus sylvestris) are useful for maintaining isolates.

Assay species

Chenopodium quinoa is a good local lesion host. Anthriscus cerefolium is a good test plant in aphid-transmission experiments.

Strains

Isolates from parsnip differ serologically and also to some extent in host range from Anthriscus sylvestris isolates (Murant & Goold, 1968). Isolates from Heracleum sphondylium seem identical to parsnip isolates (El Nagar & Murant, 1974).

Transmission by Vectors

Transmitted in the semi-persistent manner by the aphid Cavariella aegopodii. C. pastinacae also transmits, but not C. theobaldi. Transmission by C. aegopodii depends on the presence in the source plant of a helper virus, anthriscus yellows (Murant & Goold, 1968). Anthriscus yellows virus is also semi-persistent in the vector (El Nagar & Murant, 1973) but is not transmissible by inoculation of sap. Parsnip yellow fleck virus is therefore not transmitted by aphids from manually inoculated plants, nor from plants, such as parsnip or carrot, which are immune to anthriscus yellows virus (Murant & Goold, 1968). However, an exception to this generalization is that aphids already carrying anthriscus yellows virus can acquire parsnip yellow fleck virus from singly infected plants; they can also acquire it by feeding through membranes on plant extracts or purified virus preparations (El Nagar & Murant, 1973). Carrot red leaf virus, which assists transmission of carrot mottle virus (Murant, 1974) does not act as a helper for parsnip yellow fleck virus (Murant & Goold, 1971).

C. aegopodii can acquire both dependent and helper viruses after minimum acquisition feeding times of 10-15 min and can inoculate in 2 min, with no latent period, but transmission efficiency increases with increasing acquisition and inoculation feeding times up to 24 h. However, aphids already carrying anthriscus yellows virus can acquire parsnip yellow fleck virus in 2 min. Starving the aphids for 3 h before acquisition of either virus, or both together, does not improve the efficiency of transmission. Infective adult aphids retain the ability to inoculate both viruses for up to 4 days but infective larvae lose ability to inoculate the viruses on moulting (Murant & Goold, 1968; El Nagar & Murant, 1973).

Transmission through Seed

No reports.

Transmission by Dodder

No information.

Serology

Moderately to highly immunogenic. Antibody titres of 1/4096 have been obtained. Gel-diffusion tests, in which the virus gives one line of precipitate, and ring-precipitin tests, give satisfactory results (Murant & Goold, 1968). Passive haemagglutination and latex flocculation tests have also proved useful in studies of the multiplication of this virus (Abu Salih, 1968; Abu Salih, Murant & Daft, 1968a, 1968b, and unpublished).

Relationships

All tested isolates from parsnip and Heracleum sphondylium appear to be serologically identical but differ from Anthriscus sylvestris isolates. The extent of the apparent difference is moderate or great depending on the specificity of the antisera used. In one-way plant-protection tests, plants infected with an Anthriscus isolate developed no additional symptoms when challenge-inoculated with a parsnip isolate, but the latter was recovered from some plants (Murant & Goold, 1968).

Stability in Sap

In Spinacia oleracea sap, the virus lost infectivity after 10 min at 57.5-65°C, storage at room temperature for 4-7 days, or dilution to 10-3-10-4. In Chenopodium quinoa assay plants, the decrease in lesion number with dilution is proportional to the dilution factor (Murant & Goold, 1968; Abu Salih, 1968).

Purification

A modification of Steere’s butanol/chloroform method is useful (Murant & Goold, 1968). Yields of virus are very dependent on the environmental conditions in which the source plants are kept. In Scotland, little multiplication occurs in Spinacia oleracea plants kept in the glasshouse in summer. Best yields are obtained when the plants are placed after inoculation in growth chambers at 15°C, illuminated (10,000 lux) for 8 h per day, and the systemically infected leaves harvested 19 days after the plants are inoculated (Abu Salih, 1968).

Properties of Particles

There is a single centrifugal component, with a sedimentation coefficient (s°20,w) of 148 S (A. F. Murant & H. Barker, unpublished data).

In immunoelectrophoresis, using 0.025 ionic strength barbitone acetate buffer, pH 8.6, the particles migrate heterogeneously towards the anode, producing a single precipitin line, without spurs, trailing to the origin.

A260/A280: c. 1.75.

Particle Structure

Particles are isometric, c. 30 nm in diameter (Fig.6). They disintegrate when mounted in phosphotungstate for electron microscopy, even when previously fixed in formaldehyde, but are well preserved in 2% uranyl acetate.

Particle Composition

Nucleic acid: RNA, single-stranded. Only one component detected, of M. Wt c. 3.7 x 106 (Murant, Mayo & Goold, 1974).

Protein: Purified virus yields protein preparations which produce three poorly resolved bands in polyacrylamide gel electrophoresis with estimated M. Wt of c. 30,000, 27,000 and 22,000. It is not clear whether these represent distinct polypeptides or derivatives of a single polypeptide (Murant, Mayo & Goold, 1974).

Relations with Cells and Tissues

In spinach, Nicotiana clevelandii and Anthriscus cerefolium, the virus induces the formation of inclusion bodies composed of vesicles and, especially in mature inclusion bodies, straight tubules c. 30 nm in diameter (Fig.7, Fig.8). Infected cells also possess plasmodesmatal and cytoplasmic tubules c. 45 nm in diameter containing virus particles; plasmodesmatal tubules are sheathed by cell wall outgrowths. Tubules containing virus particles also occur in the lumen of sieve tubes (Murant, Roberts & Hutcheson, 1973).

Notes

Parsnip yellow fleck virus has a combination of properties unlike those of any other well-characterized virus. It is the only semi-persistent aphid-borne virus known to have isometric particles. It resembles another virus affecting umbellifers, carrot mottle (Murant, 1974) in depending on a second virus for transmission by aphids (Watson, Serjeant & Lennon, 1964), but the two viruses are dissimilar and unrelated.

Parsnip yellow fleck virus is the commonest virus found in parsnip in the UK (Murant & Goold, 1968), often occurring in mixed infections with other viruses, especially parsnip mosaic (Murant, 1972) and parsnip mottle (Watson et al., 1964). Its economic importance is unknown. It is readily distinguished from parsnip mosaic virus (which has filamentous particles), and from other uncharacterized viruses found in parsnip in the UK (Murant & Goold, 1968), by symptoms in Chenopodium amaranticolor and C. quinoa, by infecting spinach and Nicotiana clevelandii systemically, and by the characteristic symptoms in chervil.

References

  1. Abu Salih, Ph.D. Thesis, University of St. Andrews, 1968.
  2. Abu Salih, Murant & Daft, J. gen. Virol. 2: 155, 1968a.
  3. Abu Salih, Murant & Daft, J. gen. Virol. 3: 299, 1968b.
  4. El Nagar & Murant, Rep. Scott. hort. Res. Inst., 1972: 66, 1973.
  5. El Nagar & Murant, Rep. Scott. hort. Res. Inst., 1973: 66, 1974.
  6. Murant, CMI/AAB Descriptions of Plant Viruses 91, 4 pp., 1972.
  7. Murant, CMI/AAB Descriptions of Plant Viruses 137, 4 pp., 1974.
  8. Murant & Goold, Ann. appl. Biol. 62: 123, 1968.
  9. Murant & Goold, Rep. Scott. hort. Res. Inst., 1970: 53, 1971.
  10. Murant, Mayo & Goold, Rep. Scott. hort. Res. Inst., 1973: 67, 1974.
  11. Murant, Roberts & Hutcheson, Rep. Scott. hort. Res. Inst., 1972: 66, 1973.
  12. Watson, Serjeant & Lennon, Ann. appl. Biol. 54: 153, 1964.
  13. Wolf & Schmelzer, Zentbl. Bakt. ParasitKde, Abt. 2: 127: 665, 1972.

Acknowledgements

Photographs: Scottish Horticultural Research Institute.


Figure 1

Fine vein-yellowing symptom in leaf of naturally infected Pastinaca sativa (parsnip).

Figure 2

Yellow fleck symptom in leaf of naturally infected parsnip.

Figure 3

Systemic necrosis of youngest leaf of Anthriscus cerefolium (chervil).

Figure 4

Local lesions in Chenopodium quinoa.

Figure 5

Local and systemic symptoms in Spinacia oleracea (spinach).

Figure 6

Particles mounted in 2% uranyl acetate. Bar represents 100 nm.

Figure 7

Ultrathin section of systemically infected spinach leaf cell, showing inclusion body (I) adjacent to the nucleus (N). Bar represents 2 µm.

Figure 8

Detailed structure of the inclusion body which consists of bundles of straight tubules, small vesicles, and whorls of membranes. Bar represents 500 nm.