172
September 1977
Family: Potyviridae
Genus: Bymovirus
Species: Rice necrosis mosaic virus
Acronym: RNMV


Rice necrosis mosaic virus

T. Inouye
College of Agriculture, University of Osaka Prefecture, Sakai, Osaka, Japan

S. Fujii
Okayama Prefectural Agricultural Experiment Station, Sanyo-Cho, Okayama, 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 Fujii et al. (1966, 1967).

A soil-borne virus with slightly flexuous filamentous particles of at least two lengths, c. 275 and 550 nm, and 13-14 nm in width. It is sap-transmissible with difficulty and is transmitted in soil; the fungus Polymyxa graminis is thought to be a vector. Rice is the only known host. Found in Japan.

Main Diseases

Causes mosaic symptoms in rice (Oryza sativa) characterized by spindle shaped yellow flecks and streaks (Fig.1) visible on the lower leaves but usually not on the newly growing leaves. Causes necrotic fleck lesions on the basal portions of stems and sheaths in some plants (Fig.2). Infected plants are moderately stunted; the tillers are decreased in number, and somewhat prostrate.

Occurs in rice that is transplanted from upland nurseries to paddy fields or direct-seeded in upland fields; rare in rice transplanted from lowland nurseries to paddy fields or direct-seeded in paddy fields (Fujii, 1975). Paddy rice with necrosis mosaic disease often suffers also from rice blast (Pyricularia oryzae) especially on panicles and nodes, resulting in a great reduction of yield (Fujii, 1975).

Geographical Distribution

Japan.

Host Range and Symptomatology

Rice is the only known host. Most of the Japanese paddy rice varieties can be infected by growing in infective soil. Kanto No. 52 and several other varieties are found to be the most resistant (Fujii, 1975). Other tested species of Gramineae and dicotyledonous plants, including Hordeum vulgare, Triticum aestivum, Avena sativa, Zea mays, Chenopodium amaranticolor, C. quinoa, and Nicotiana tabacum did not develop symptoms when grown in infective soil or after inoculation with infective sap (Fujii, 1975; T. Inouye, unpublished data).

Diagnostic species

Oryza sativa (rice). Leaf mottling, usually becoming visible on a few lower leaves at the maximum tillering stage about 70 days after sowing in infective soil, is characterized by spindle shaped yellow flecks and streaks (Fig.1). With subsequent growth of the plants, the symptoms spread successively to the upper leaves, but are usually not visible on the newly produced leaves. Optimum conditions for virus infection are low soil moisture content and a soil temperature of 25-30°C (Fujii, 1975).

Propagation species

Oryza sativa (rice). The Japanese paddy rice varieties, Akebono, Kibiyoshi, Norin No. 22, or any others that show symptoms in the field, are suitable.

Assay species

No known local lesion host. The virus may be assayed by counting the proportion of rice plants that become diseased.

Strains

No strains reported.

Transmission by Vectors

Fujii (1975) suggested that the soil-inhabiting fungus, Polymyxa graminis (Fig.4), is the vector of the virus because (1) steamed soil became infective on addition of an extract of rice roots naturally infected with the virus, (2) P. graminis was frequently found in the roots of naturally infected rice, (3) invasion of root hairs of rice seedlings by zoospores of the fungus was observed on the second day after sowing in infective soil, (4) steamed soil became infective on addition of resting spores of P. graminis collected from rice roots naturally infected with the virus, and the fungus was consistently found in the roots of rice experimentally infected, (5) seedlings grown in upland rice nurseries had more of the fungus in their roots than did seedlings grown in lowland nurseries.

Transmission through Seed

Fujikawa et al. (1972) reported 2.6-5.3% of seeds from infected plants carried the virus, but Fujii (1975) found no seed transmission in about 16,000 rice seedlings.

Transmission by Dodder

Not reported.

Serology

Serum from a rabbit injected intramuscularly with partially purified virus reacted with the virus to a titre of 1/80 in micro-precipitin tests (T. Inouye, unpublished data).

Relationships

Rice necrosis mosaic virus is closely serologically related to barley yellow mosaic and wheat yellow mosaic viruses (Usugi & Saito, 1976). It resembles barley yellow mosaic (Inouye & Saito, 1975), oat mosaic (Hebert & Panizo, 1975), wheat spindle streak mosaic (Slykhuis, 1976) and wheat yellow mosaic (Saito et al., 1968; Inouye, 1969) viruses in its soil transmissibility, its particle morphology, and in inducing pinwheel-type inclusions and membraneous network structures in the cytoplasm of infected plant cells.

Stability in Sap

In rice plant sap, the thermal inactivation point is 60-65°C, dilution end point is 1/5000-1/10,000, and longevity in vitro at room temperature is 7-14 days (Fujikawa et al., 1970).

Purification

1. Fujii (1975): homogenize rice tissue in 6 volumes of 0.2 M phosphate buffer (pH 7.4) containing 0.1% thioglycollic acid and 2% Triton X-100. Add 2 volumes of a 1:1 mixture of chloroform and n-butanol and clarify by low speed centrifugation. Resuspend the pellets from high speed centrifugation in 0.03 M phosphate buffer (pH 7.4). Purify further by sucrose density-gradient centrifugation.

2. T. Inouye (unpublished data): pulverize infected tissue in liquid nitrogen, then add 3 volumes of 0.05 M borax containing 0.001 M ethylenediamine-tetraacetic acid (EDTA). Express juice through cheesecloth, clarify by adding 0.2 volume of chloroform and concentrate by 3 cycles of differential centrifugation. Resuspend the pellets from high speed centrifugation in 0.05 M borate buffer (pH 7.6).

Properties of Particles

Not known.

Particle Structure

Particles (Fig.5) are slightly flexuous filaments 13-14 nm in diameter and having at least two modal lengths (275 and 550 nm) in leaf dip and partially purified preparations (Inouye, 1968).

Particle Composition

Unknown.

Relations with Cells and Tissues

In cells of epidermal strips from the inside surface of the leaf sheath of infected rice, large intracellular inclusions (X-bodies) are observed (Fig.3). In ultrathin sections, characteristic laminated aggregate inclusions (Fig.6, Fig.7) are observed in the cytoplasm; scattered or loosely aggregated virus particles are often associated with the laminated aggregates (Fig.7). Membraneous network structures occur in the cytoplasm (Fig.8) but are less common than the laminated aggregates (Inouye, 1970; Fujii, 1975).

Notes

Rice necrosis mosaic virus can be readily distinguished from other viruses that infect rice in Japan by its particle morphology and transmissibility in soils and by inoculation of sap. All the other viruses are transmitted by leafhoppers but not by sap or through soil; rice dwarf (Iida et al., 1972), rice black-streaked dwarf (Shikata, 1974) and rice waika (Yokoyama & Sakai, 1975; Nishi et al., 1975; Doi et al., 1975) viruses have spherical particles, and rice stripe virus (Koganezawa et al., 1975) has branched filamentous particles having super-coiled helical structure.

References

  1. Doi, Yamashita, Kusunoki, Arai & Yora, Ann. Phytopath. Soc. Japan 41: 228, 1975.
  2. Fujii, Thesis, Univ. Tokyo, 1975.
  3. Fujii, Okamoto, Idei & Inouye, Ann. Phytopath. Soc. Japan 32: 325, 1966.
  4. Fujii, Okamoto, Idei, Shiomi, Inouye, Inouye, Mitsuhata & Asatani, Ann. Phytopath. Soc. Japan 33: 105, 1967.
  5. Fujikawa, Tomiki & Sato, Nogyo oyobi Engei 45: 1419, 1970.
  6. Fujikawa, Tomiki & Sato, Ann. Phytopath. Soc. Japan 38: 213, 1972.
  7. Hebert & Panizo, CMI/AAB Descriptions of Plant Viruses 145, 4 pp., 1975.
  8. Iida, Shinkai & Kimura, CMI/AAB Descriptions of Plant Viruses 102, 4pp., 1972.
  9. Inouye, Ann. Phytopath. Soc. Japan 34: 301, 1968.
  10. Inouye, Nogaku Kenkyu 53: 61, 1969.
  11. Inouye, Ann. Phytopath. Soc. Japan 36: 186, 1970.
  12. Inouye & Saito, CMI/AAB Descriptions of Plant Viruses 143, 3 pp., 1975.
  13. Koganezawa, Doi & Yora, Ann. Phytopath. Soc. Japan 41:148, 1975.
  14. Nishi, Kimura & Maejima, Ann. Phytopath. Soc. Japan 41: 223, 1975.
  15. Saito, Tsuchizaki & Hibino, Ann. Phytopath. Soc. Japan 34: 347, 1968.
  16. Shikata, CMI/AAB Descriptions of Plant Viruses 135, 4 pp., 1974.
  17. Slykhuis, CMI/AAB Descriptions of Plant Viruses 167, 3 pp., 1976.
  18. Usugi & Saito, Ann. Phytopath. Soc. Japan 42: 12, 1976.
  19. Yokoyama & Sakai, Ann. Phytopath. Soc. Japan 41: 219, 1975.


Figure 1

Rice leaves: (left) healthy leaf, (right and centre) leaves showing mosaic symptoms.

Figure 2

Necrosis in the basal portions of stems of infected rice.

Figure 3

X-bodies in epidermal cells of inside surface of leaf sheath of infected rice. (N) nucleus; (X) X-body.

Figure 4

Polymyxa graminis in cells of a rice root; (P) plasmodium just about to divide into resting spores; (R) resting spore cluster; (M) meront.

Figure 5

Virus particles in dip preparation shadowed with chromium. Bar represents 500 nm.

Figure 6

A piece of laminated aggregate inclusion in dip preparation shadowed with chromium. Bar represents 500 nm.

Figure 7

Section of infected leaf cell showing laminated aggregate inclusions and filamentous virus particles. Bar represents 500 nm.

Figure 8

Section of infected leaf cell showing membraneous structure. Bar represents 500 nm.