Rice yellow mottle virus
State Agricultural College, Prof. H. C. van Hallstraat 1, Groningen, The Netherlands
An RNA-containing virus with isometric particles about 25 nm in diameter,
infecting species of
Gramineae only. It is readily transmissible by inoculation of sap and also by several
beetles. Reported in rice from Kenya.
In rice (Oryza sativa
) the virus causes a yellow or orange leaf discolouration,
and sterility. Infected plants are found first near the bunds
but soon thereafter whole
fields may be affected.
Reported from the Kisumu area near Lake Victoria in Western Kenya
Host Range and Symptomatology
Host range is narrow, being restricted to species in the Gramineae, mainly in the tribes
and Eragrostideae. Symptoms, when induced, consist initially of systemic mottling.
Some grass species
develop symptoms soon after mechanical inoculation of sap and are used as experimental hosts
- Oryza sativa (rice). Symptoms are induced in seedlings of all rice varieties
tested. About a
week after inoculation yellow dots appear at the bases of the youngest systemically
The dots elongate parallel to the veins; leaves formed later are mottled
and often spirally
twisted. Plants are stunted, form few tillers and no panicles. In cv. Basmati 217
early symptoms are
difficult to discern.
- Oryza punctata. Young systemically infected leaves show only a few elongated
- Dinebra retroflexa. Mild mottling and yellowish-green discolouration of
- Phleum arenarium. Obvious mottling of the systemically infected leaves
(Fig.3) which later
turn yellow and die.
- O. sativa cv. Sindano is a suitable plant for maintaining cultures and a
good source of virus
for purification. Other rice varieties are probably suitable too.
- No known local lesion host. O. sativa cvs. Sindano and IR 20 are suitable
Transmission by Vectors
Transmissible by chrysomelid beetles belonging to the subfamilies Criocerinae,
Galerucinae (Sesselia pusilla
), Halticinae (Chaetocnema
spp.) and Hispinae
). The long-horned grasshopper Conocephalus merumontanus
transmits the virus
carries the virus in the
field. S. pusilla, C. pulla
and T. sericea
sometimes acquire the virus
in 15 min and
also sometimes inoculate in 15 min. Percentage of insects transmitting increases
with increasing length
of acquisition and inoculation feeds up to 2-3 days. S. pusilla
and C. pulla
virus usually for 2-3 days, and sometimes for 8 and 5 days respectively,
whereas T. sericea
retains the virus for one day only
Transmission through Seed
Apparently not seed-transmitted in rice.
Transmission by Dodder
The virus is strongly immunogenic, inducing antibody titres of up to 1/4096.
It forms only one
band of precipitate in agar gel-diffusion tests using 1% agar and antiserum prepared
by a series of
intravenous and intramuscular injections.
The virus cannot be placed in an established group of viruses.
No serological relationship was
detected between rice yellow mottle virus and any of several other isometric viruses,
which also are beetle-transmitted in grasses
Stability in Sap
In sap from rice cv. Sindano tested on seedlings of the same variety, the thermal inactivation
point (10 min) is about 65°C, and the dilution end-point is 10-6
. The infectivity of
sap diluted with 0.01 M phosphate buffer pH 7.0 is retained for 99 days at 20°C or for 260 days
at 4°C. The virus survives for at least a year in leaf tissue stored at 4°C above
The virus is stable in vitro
and easy to purify
Use fresh or
deep-frozen young rice leaves, harvested 10-12 days after infection. Homogenize small
pieces in 0.1
M phosphate buffer pH 5.0 + 0.2% 2-mercaptoethanol (1 g of leaves/20 ml of buffer).
cloth. Emulsify extract with 0.5 vol chloroform (5 min) and centrifuge at low speed.
To each 100 ml
of the aqueous phase add 20 g (NH4
at low speed. Repeat this procedure with the supernatant fluid but this time
retain the pellets after
low speed centrifugation. Resuspend them in a small amount of buffer
pH 5.0 and dialyse against the
same buffer. Clarify by one cycle of differential centrifugation (20 min at
100 min at 78,500 g
). Suspend the sediment from high speed centrifugation
in 0.01 M
phosphate buffer pH 7.0. Dialyse against the same buffer and centrifuge at low speed.
Work at room
temperature during precipitation of the virus with
during the first dialysis, otherwise at 4°C. Yield is about 1 mg virus/g of leaves.
Properties of Particles
Sedimentation coefficient (s
) in 0.01 M phosphate buffer pH 7.0:
about 109 S. No accessory viral components are found by analytical centrifugation.
virus in water or buffer does not withstand freezing.
Absorbance at 260 nm
(1 mg/ml, 1 cm light path):
Particles are isometric, about 25 nm in diameter
No obvious surface structure is
revealed in phosphotungstate negative stain.
Some particles are penetrated by phosphotungstate.
Particle CompositionNucleic acid:
RNA, single-stranded, M. Wt about 1.4 x 106
; constitutes about
23% of particle weight. Molar percentages of nucleotides: G29; A21; C25; U25.
Protein: no information.
Relations with Cells and Tissues
In rice cv. Sindano the virus is found free in the cytoplasm of epidermis and mesophyll cells.
Aggregates of virus particles are common in mesophyll cells of young leaves.
Long flexuous tubules
inclusions with electron-dense centres and aggregates of fibrils are observed by electron
The virus is easily differentiated from other known viruses occurring naturally in rice
by being mechanically transmissible. Among other viruses affecting grasses it resembles
and phleum mottle
Benigno & ABrook, 1972
viruses in having beetle vectors and in several other properties.
Although it resembles phleum mottle
virus in infecting Phleum arenarium,
it differs in being unable to infect
and P. pratense
- Benigno & ABrook, Ann. appl. Biol. 72: 43, 1972.
- Bakker, Neth, J. Pl. Path. 76: 53, 1970.
- Bakker, Agric. Res. Reports 829: 152 pp., 1974.
- Catherall, Pl. Path. 19: 101, 1970.
- Serjeant, Ann. appl. Biol. 59: 31, 1967.
- Ou, in Rice Diseases, Commonwealth Mycological lnstitute, Kew, 368 pp., 1972.
Field infected rice cv. Sindano.
Field infected rice cv. Sindano.
Systemic symptoms in mechanically infected Phleum arenarium.
Mottling of rice cv. Sindano leaves induced by mechanical inoculation.
Adult of the chrysomelid beetle, Chaetocnema pulla.
Virus particles from a purified preparation stained with phosphotungstate.
Bar represents 100 nm.
Flexuous tubules in epidermal cell of mature leaf of RYMV-infected rice cv.
represents 500 nm.