84
June 1972
Family: Potyviridae
Genus: Potyvirus
Species: Papaya ringspot virus
Acronym: PRSV

There is a more recent description of this virus: DPV 292

Papaya ringspot virus

D. E. Purcifull
Plant Virus Laboratory, Plant Pathology Department, University of Florida, Gainesville, Florida, USA

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 Jensen (1949a), Conover (1962, 1964a), De Bokx (1965) and Zettler, Edwardson & Purcifull (1968).

Synonyms

The following incompletely studied viruses may be synonyms:
Papaya (papaw) distortion ringspot virus (Rev. appl. Mycol. 41: 530)
Papaya (papaw) mosaic virus (Rev. appl. Mycol. 28: 131)

A virus with flexuous, filamentous particles about 800 nm long. It is stylet-borne by aphids, is sap-transmissible, and has a narrow host range. Causes a disease of major importance in papaya.

Main Diseases

In papaya, it causes mottling and distortion of leaves, rings and spots on fruit, and streaks on stems and petioles. It stunts the plants and diminishes fruit production (Conover, 1964a).

Geographical Distribution

In most tropical and subtropical areas of the world where papayas are grown.

Host Range and Symptomatology

Host range is narrow; 11 species in three dicotyledonous families (Caricaceae, Chenopodiaceae and Cucurbitaceae) have been experimentally infected, but papaya is the only reported natural host. Sap-transmissible.

Diagnostic species

Carica papaya (papaya). Symptoms in papaya are variable. Seedlings show vein-clearing and downward cupping of the young systemically infected leaves about 2 weeks after inoculation. After several weeks, leaves may become mottled (Fig.3) and deformed, the lobes being markedly reduced in size (Fig.1). Among other species of Carica tested, some were susceptible and some were not (Conover, 1964a).

Cucurbita pepo (summer squash and pumpkin). Yellow chlorotic areas appear along minor veins in systemically infected squash leaves 10-14 days after inoculation (Fig.5), followed by mottle and some leaf distortion. Symptoms in pumpkin are similar, but generally milder.

Propagation species

Papaya, squash and pumpkin are useful for maintaining cultures. Pumpkin has been used as a source of virus for purification (Milne & Grogan, 1969).

Assay species

Chenopodium amaranticolor develops local lesions (Cook & Milbrath, 1971). Pumpkin is useful for vector studies.

Strains

A minor variant designated ‘faint mottle ringspot’ induces milder symptoms in Carica papaya than does the strain common in Florida (Conover, 1964a, 1964b).

Transmission by Vectors

Transmitted by several species of aphids in a non-persistent manner, notably Myzus persicae (Jensen, 1949b; Conover, 1964a; Zettler et al., 1968). Other vectors are Aphis gossypii, A. medicaginis, A. rumicis, Macrosiphum solanifolii and Micromyzus formosanus (Jensen, 1949b).

Transmission through Seed

None detected in papaya (De Bokx, 1965).

Transmission by Dodder

No information.

Serology

An antiserum was obtained by injecting rabbits with clarified sap from infected papaya leaves (Story & Halliwell, 1969b). Liquid precipitin tests with purified virus and immunodiffusion tests with detergent-treated virus are useful for studying serological relationships (Milne & Grogan, 1969).

Relationships

The virus is serologically related to watermelon mosaic virus (Milne & Grogan, 1969) but the degree of relationship is not clear; its general properties place it in the potato virus Y group of viruses (Brandes & Bercks, 1965).

Stability in Sap

In papaya sap, the virus loses infectivity after 10 min at 54-56°C and after 8 hr at room temperature. The dilution end-point is about l0-3 (Conover, 1964a).

Purification

Partially purified virus for serological tests was obtained from infected pumpkin leaves using a method developed for watermelon mosaic virus (Milne & Grogan, 1969). Tissue was homogenized in 0.3 M potassium phosphate buffer, pH 7.6 (2 ml/g tissue). The extract was clarified with n-butanol and the virus obtained by two cycles of differential centrifugation.

Properties of Particles

No information.

Particle Structure

Flexuous filaments (Fig.6) 800 nm long and 12 nm in diameter (Herold & Weibel, 1962).

Particle Composition

No information.

Relations with Cells and Tissues

Cytoplasmic inclusions (Fig.2) have been observed in stained epidermal strips of squash (Christie, 1971). Pinwheel inclusions (Fig.4) are seen in the cytoplasm of infected tissues (Zettler et al., 1968; Story & Halliwell, 1969b). In negatively stained extracts from infected leaves the striated nature of these inclusions is revealed (Fig.7). Virus particles have been observed in the cytoplasm of infected cells (Herold & Weibel, 1962).

Notes

Numerous mosaic virus diseases of papaya have been reported from various parts of the world (Adsuar, 1947; Capoor & Varma, 1958; Ishii & Holtzmann, 1963; Kulkarni, 1970; Namba & Kawanishi, 1966; Pozdena, 1967; Singh, 1969). They resemble papaya ringspot in some respects, but the precise relationship of the causal viruses has not been determined. They should not be confused, however, with the papaya mosaic virus described by Conover (1962, 1964b), De Bokx (1965) and Zettler et al. (1968). Papaya mosaic virus is a flexuous rod 530 nm long, is not aphid-transmitted, and is a member of the potato virus X group (Brandes & Bercks, 1965). Watermelon mosaic virus, to which papaya ringspot virus is serologically related, does not infect papaya (Milne & Grogan, 1969).

A mycoplasma-like organism has been associated with the leafhopper-borne bunchy top disease of papaya (Story & Halliwell, 1969a). The virus diseases of papaya have been reviewed recently by Cook (1972).

References

  1. Adsuar, J. Agric. Univ. P. Rico 31: 248, 1947.
  2. Brandes & Bercks, Adv. Virus Res. 11: 1, 1965.
  3. Capoor & Varma, Indian J. agric. Sci. 28: 225, 1958.
  4. Christie, Proc. Fla Pest Control Conf. 5: 65, 1971.
  5. Conover, Phytopathology 52: 6, 1962.
  6. Conover, Proc. Fla St. hort. Soc. 77: 440, 1964a.
  7. Conover, Proc. Fla St. hort. Soc. 77: 444, 1964b.
  8. Cook, Tech. Bull. Fla agric. Exp. Stn 750, 19 pp., 1972.
  9. Cook & Milbrath, Pl. Dis. Reptr 55: 785, 1971.
  10. De Bokx, Pl. Dis. Reptr 49: 742, 1965.
  11. Herold & Weibel, Virology 18: 302, 1962.
  12. Ishii & Holtzmann, Pl. Dis. Reptr 47: 947, 1963.
  13. Jensen, Phytopathology 39: 191, 1949a.
  14. Jensen, Phytopathology 39: 212, 1949b.
  15. Kulkarni, Ann. appl. Biol. 66: 1, 1970.
  16. Milne & Grogan, Phytopathology 59: 809, 1969.
  17. Namba & Kawanishi, J. econ. Ent. 59: 669, 1966.
  18. Pozdena, Proc. Sixth Conf. Czechoslovak Plant Virologists, Prague, 1967.
  19. Singh, Pl. Dis. Reptr 53: 267, 1969.
  20. Story & Halliwell, Phytopathology 59: 1336, 1969a.
  21. Story & Halliwell, Pl. Dis. Reptr 53: 757, 1969b.
  22. Zettler, Edwardson & Purcifull, Phytopathology 58: 332, 1968.


Figure 1

Leaf distortion in papaya.

Figure 2

Photomicrograph of cytoplasmic inclusion-body (arrow) in epidermal cell of squash. Bar represents 20 µm.

Figure 3

Mottle in papaya leaf.

Figure 4

Cytoplasmic pinwheel and scroll inclusions in papaya leaf cell. Bar represents 250 nm.

Figure 5

Veinal chlorosis in systemically infected squash leaf, 2 weeks after inoculation.

Figure 6

Electron micrograph of filamentous particles mounted in phosphotungstate. Bar represents 1 µm.

Figure 7

Striated, cytoplasmic inclusion in leaf extract, mounted in phosphotungstate. Bar represents 100 nm.