102
October 1972
Family: Reoviridae
Genus: Phytoreovirus
Species: Rice dwarf virus
Acronym: RDV


Rice dwarf virus

T. T. Iida
Institute for Plant Virus Research, 959 Aobacho, Chiba, Japan

A. Shinkai
Institute for Plant Virus Research, 959 Aobacho, Chiba, Japan

I. Kimura
Institute for Plant Virus Research, 959 Aobacho, Chiba, Japan

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 Takata (1895-6) and Fukushi (1931, 1934).

Selected synonyms

Rice stunt (Rev. appl. Mycol. 30: 488)
Rice mosaic virus (Rev. appl. Mycol. 19: 229)
Oryza virus 1 (Rev. appl. Mycol. 36: 303)
Marmor oryzae (Rev. appl. Mycol. 19: 229)

A virus with isometric particles, about 70 nm in diameter, containing double-stranded RNA. Infects rice and a few other graminaceous species. Transmitted in the persistent manner by leafhoppers. The virus multiplies both in plants and leafhoppers, and passes through leafhopper eggs to a high proportion of the progeny.

Main Diseases

Dwarf (or stunt) disease of rice, in Japanese called ine isyuku-byô (ine ishuku-byo).

Geographical Distribution

Japan and Korea. A disease of rice in the Philippines formerly thought to be rice dwarf is now considered different (Rivera & Ou, 1965).

Host Range and Symptomatology

Host range is restricted to a few species of Gramineae (Fukushi, 1934; Shinkai, 1962).

Diagnostic species

Oryza sativa (rice). General stunting and fine chlorotic specks on foliage (Fig.1, Fig.2).

Echinochloa crus-galli var. oryzicola. Symptoms similar to those in rice.

Propagation species

Oryza sativa.

Assay species

Oryza sativa. Young seedlings are suitable for assaying transmission by vectors. Virus samples can be assayed by injecting them into vector nymphs, which are then tested for transmission after an appropriate period of incubation (Fukushi & Kimura, 1959).

Strains

None reported.

Transmission by Vectors

Transmissible by the leafhoppers Nephotettix cincticeps (Fig.3), N. apicalis (Fig.4), and Inazuma dorsalis (Fig.4), but not by N. impicticeps (= N. bipunctatus) (Fukushi, 1934, 1937; Nasu, 1963; Shinkai, 1962). The principal vector in the field is N. cincticeps. Few individuals of these species are potential transmitters, the proportion among field populations differing with the locality. With N. cincticeps, the majority of potential transmitters acquire virus by feeding for 1 day on diseased rice plants. Young nymphs are more efficient, and exceptionally can acquire virus by feeding only for 1 min. Following virus acquisition, there is an incubation period of 12-25 days, after which the leafhoppers transmit virus almost until their death. About half of the transmitting individuals can inoculate virus to healthy rice seedlings in a 30-min feed; the minimum inoculation feeding period reported is 3 min. The virus passes through the leafhopper eggs to a high proportion of the progeny, notably in N. cincticeps (Fukushi, 1934, 1940; Shinkai, 1962). Nymphs of I. dorsalis infected through the egg tend to die prematurely (Shinkai, 1962).

Transmission through Seed

Not seed-transmitted in rice (Fukushi, 1934).

Transmission by Dodder

None reported.

Serology

Antisera with titres of 1/2000-1/8000 can be produced in rabbits by intramuscular injection of purified virus in adjuvant. Antisera react in precipitin or agar gel-diffusion tests with virus antigen in both plant and insect extracts (Kimura, 1962). Precipitin ring tests and ring-time tests have been used to measure virus concentrations in various parts of infected rice plants. Fluorescein-conjugated antibody can be employed to detect virus antigen in smears of individual insects or in infected rice plants (I. Kimura & S. Miyashima, unpublished).

Relationships

In particle morphology, rice dwarf virus and wound tumor virus closely resemble each other, but no serological relationship has been detected (I. Kimura & L. M. Black, unpublished). Rice dwarf virus and rice black-streaked dwarf virus showed no mutual protection in rice plants (Shinkai, 1961).

Stability in Sap

In extracts of the leafhopper vector, the thermal inactivation point (10 min) is 45-50°C, and the dilution end-point is 10-4-10-5; infectivity survived storage for 48 h at 4°C. Infectivity survived for at least 1 year in rice leaves and in leafhopper vectors stored at -40°C (Fukushi & Kimura, 1959; Kimura & Fukushi, 1960).

Purification

Purify from infected rice leaves by grinding them in 0.1 M phosphate buffer (pH 6.8, containing 0.01 M ascorbate), shaking the extracts first with CCl4 (1:3 in volume) for 1-2 min, and then with Difron S3 (trifluorotrichloroethane, 1:3 in volume), and subjecting the final aqueous phase to one cycle of differential centrifugation. Further purification is achieved by rate zonal and quasi-equilibrium zonal density gradient centrifugation (Kimura, Kodama & Suzuki, 1968).

Properties of Particles

The particles appear to be of two types, intact 510 S particles containing RNA, and empty shells (S value undetermined) without RNA (Y. Kawade, I. Kimura, T. Kodama & N. Suzuki, unpublished).

Particle Structure

The particles are icosahedral, about 70 nm in diameter (Fig.5), with 32 capsomeres of which 12 consist of 5 structural subunits and 20 consist of 6 structural subunits (Fukushi, Shikata & Kimura, 1962; Kimura & Shikata, 1968).

Particle Composition

RNA: About 11% of particle weight is double-stranded RNA, with a composition of 44% G + C (Miura, Kimura & Suzuki, 1966; Sato et al., 1966). RNA extracted from purified virus consisted of 12 segments of different lengths (Fujii-Kawata & Miura, 1970), but was not infective (I. Kimura, unpublished).

Protein: No information.

Relations with Cells and Tissues

In diseased rice plants, chlorotic cells often contain a single intracellular body, usually near the cell nucleus (Fukushi, 1931). Using the fluorescent-antibody technique, virus antigen was located in these intracellular bodies, notably in cells adjacent to the vascular bundles (Suzuki, Kimura & Kodama, 1968). Virus particles can also be observed by electron microscopy in these cells. They are found in the cytoplasm, either loosely scattered or in clusters; sometimes they are surrounded by thin membranes, or arranged in rows within tubular sheath structures (Shikata, 1966).

In viruliferous leafhoppers, abnormalities occur in fat body cells and mycetocytes (Nasu, 1963). Virus particles are found by electron microscopy in the cells of the alimentary canal, Malpighian tubules, salivary glands, mycetome and fat body (Fukushi & Shikata, 1963a, 1963b; Nasu, 1965; Shikata, 1966). They are found in the cytoplasm, either loosely scattered or in clusters, sometimes in a crystalline arrangement, or contained in tubular sheath structures. The virus particles appear to adhere selectively to the surface of an intracellular symbiont (‘L-symbiote’), and during passage into the leafhopper egg, the virus appears to enter the oocyte together with this symbiont from the mycetocyte of the ovariole (Nasu, 1965).

Smaller virus-like particles, occurring either in loose clusters or in crystalline arrangements, are frequently found associated with true virus particles in cells of vector insects, but their nature is obscure (Nasu, 1965). The virus particles and the smaller virus-like particles were also observed in cell cultures derived from leafhopper embryos, when they were inoculated in vitro with crude virus preparations (Mitsuhashi & Nasu, 1967).

References

  1. Fujii-Kawata & Miura, J. molec. Biol. 51: 247, 1970.
  2. Fukushi, Trans. Sapporo nat. Hist. Soc. 12: 35, 1931.
  3. Fukushi, J. Fac. Agric. Hokkaido (imp.) Univ. 37: 41, 1934.
  4. Fukushi, Proc. imp. Acad. Japan 13: 328, 1937.
  5. Fukushi, J. Fac. Agric. Hokkaido (imp.) Univ. 45: 83, 1940.
  6. Fukushi & Kimura, Proc. Japan Acad. 35: 482, 1959.
  7. Fukushi & Shikata, Virology 21: 500, 1963a.
  8. Fukushi & Shikata, Virology 21: 503, 1963b.
  9. Fukushi, Shikata & Kimura, Virology 18: 192, 1962.
  10. Kimura, Ann. phytopath. Soc. Japan 27: 204, 1962.
  11. Kimura & Fukushi, Ann. phytopath. Soc. Japan 25: 131, 1960.
  12. Kimura & Shikata, Proc. Japan Acad. 44: 538, 1968.
  13. Kimura, Kodama & Suzuki, Ann. phytopath. Soc. Japan 34: 206, 1968.
  14. Mituhashi & Nasu, Appl. Ent. Zool. 2: 113, 1967.
  15. Miura, Kimura & Suzuki, Virology 28: 571, 1966.
  16. Nasu, Bull. Kyushu agric. Exp. Stn 8: 153, 1963.
  17. Nasu, Jap. J. appl. Ent. Zool. 9: 225, 1965.
  18. Rivera & Ou, Pl. Dis. Reptr 49: 127, 1965.
  19. Sato, Kyogoku, Higuchi, Mitsui, Iitaka, Tsuboi & Miura, J. molec. Biol. 16: 180, 1966.
  20. Shikata, J. Fac. Agric. Hokkaido Univ. 55: 1, 1966.
  21. Shinkai, Ann. phytopath. Soc. Japan 26: 68, 1961.
  22. Shinkai, Bull. natn. Inst. agric. Sci., Tokyo Ser. C 14: 1, 1962.
  23. Suzuki, Kimura & Kodama, Jubilee Publ. Commem. 60th Birthday Prof. M. Sakamoto: 175, 1968.
  24. Takata, Dai- Nihon Nô-Kai-hô (J. Jap. agric. Soc.) 171: 1; 172: 13, 1895-6.


Figure 1

(Right) infected rice leaf showing fully developed chlorotic specks, (left) healthy control.

Figure 2

(Right) rice plant infected at 8-leaf stage, photographed 10 weeks after infection, (left) healthy control.

Figure 3

Nephotettix cincticeps, (left) male, (centre) female, (right) 5th instar nymph. x10.

Figure 4

Nephotettix apicalis, (left) male, and (centre) 5th instar nymph; Inazuma dorsalis, (right) male. x10.

Figure 5

Virus particles from a purified preparation, stained with phosphotungstate. Bar represents 100 nm.