Cacao yellow mosaic virus
A. A. Brunt
Glasshouse Crops Research Institute, Littlehampton, Sussex, England
Brunt et al. (1965).
A virus infecting cacao in Sierra Leone, readily transmitted by inoculation of sap
to a moderately wide range of hosts, and having isometric particles c. 28 nm in
diameter. Although no vector has yet been found, the virus is serologically distantly
related to the beetle-transmitted viruses
turnip yellow mosaic and
wild cucumber mosaic.
Naturally infected West African Amelonado cacao leaves produce large circular
chlorotic blotches which often coalesce to give a complete chlorosis or yellow mosaic
Infected trees are not severely debilitated, but the actual effect of infection
on growth and yield has not been determined. The virus occurs also, but is virtually
symptomless, in Cola nitida
and Culcasia scandens
(Blencowe et al., 1963
Recorded only from Sierra Leone
(Blencowe et al., 1963
Host Range and Symptomatology
Natural host range is narrow but the virus is transmitted readily by mechanical
inoculation of sap to members of 9 of the 21 dicotyledonous families tested.
- Theobroma cacao (cacao). Seedlings grown from inoculated Amelonado cacao beans
produce conspicuous chlorotic leaf mottling symptoms, usually within 20-30 days of
- Chenopodium amaranticolor. Numerous circular necrotic local lesions c.
1-2 mm in diameter within 5 days
soon followed by systemic chlorotic and
- Chenopodium quinoa. Numerous circular chlorotic local lesions 1-2 mm in diameter
within 5 days, soon becoming necrotic. Systemic symptoms usually a mosaic.
- Tetragonia expansa. Circular chlorotic local lesions 8-10 days after inoculation.
- Cacao and Vinca rosea; Chenopodium quinoa, Nicotiana clevelandii and Nicandra
physalodes are also useful sources of virus for purification.
- Chenopodium amaranticolor and C. quinoa.
None distinguished - single isolate only studied.
Transmission by Vectors
Not soil-borne or transmitted by mealybugs
(Brunt et al., 1965
not yet tested as vectors.
Transmission through Seed
Not seed-borne in cacao.
Transmission by Dodder
The virus is strongly immunogenic, antisera with titres of at least 1/8192 being
prepared without difficulty. The virus and its homologous antiserum combine well both
in conventional precipitin tube tests, producing typical granular (somatic)
precipitates, and in agar gel-diffusion tests, producing a single curved line of
precipitate adjacent to the antigen depot.
The virus reacts with antisera to
wild cucumber mosaic virus
but not with those to
turnip yellow mosaic virus
even though the last two viruses are themselves distantly
(MacLeod & Markham, 1963
Brunt et al., 1965
however, indicate that wild cucumber mosaic virus has some antigenic groups common to both
turnip yellow mosaic and cacao yellow mosaic viruses
(Brunt et al., 1965
No serological relationship has been detected between cacao yellow mosaic virus and
the following beetle-borne viruses:
Andean potato latent,
ononis yellow mosaic,
bean pod mottle,
bean (southern) mosaic,
turnip rosette and
(Brunt et al., 1965;
Gibbs et al., 1966;
Stability in Sap
In cacao leaf extracts, the thermal inactivation point (10 min) is 60-65°C,
dilution end-point about 20-3
, and infectivity is retained
for 16-32 days at 25-30°C or over 100 days at 0-4°C. Lyophilized sap stored
remains infective for over 5 years without appreciable loss of infectivity.
The virus is easily purified from cacao and other hosts. Infected cacao leaves are
homogenized in an extractant (wt./vol. = 1/20) at pH 7.0 containing 0.05 M phosphate
buffer and either 0.005 M diethyldithiocarbamate or 0.01 M thioglycollate. After clarifying
the extract by low speed centrifugation (8000 g
for 20 min), virus is
precipitated by 50% saturation with ammonium sulphate (but not ethanol or acetone), or
by ultracentrifugation (75,000 g
for 90-120 min is adequate). After
resuspension and dialysis against 0.005 M phosphate buffer, virus may be further
concentrated by ultracentrifugation. Higher yields of top
component are obtained by
precipitation with ammonium sulphate.
The virus may also be purified from Nicotiana clevelandii, Chenopodium amaranticolor
and C. quinoa by one or more cycles of differential centrifugation after
treating the extract with chloroform (25% v/v) or n-butanol (to 8.5% v/v) to aid
Purified preparations are readily fractionated into their two components by
centrifugation in sucrose density-gradient columns.
Properties of Particles
The particles are all the same size, but sediment as two components
protein shells without nucleic acid (top component),
and infective nucleoprotein
Sedimentation coefficients (s20, w) at infinite dilution: 49 and
A260/A280 (bottom component):
1.42; maximum absorbance at 263-265 nm is presumably
caused by relatively large amounts of cytidylic acid and small amounts of guanylic acid.
Electrophoretic mobilities: two components, -11.8 x 10-5 and -11.3 x
10-5 cm2 sec-1 volt-1 in 0.06 M phosphate
buffer pH 7.0. These two components apparently do not correspond to the 49 and 108
(Brunt et al., 1965).
Particles are isometric c.
28 nm in diameter
symmetry, and are composed of 180 structural subunits arranged in pentamer-hexamer
clusters (20 sixes and 12 fives) to produce 32 morphological units. Top component
particles are penetrated by 2% potassium phosphotungstate but bottom component
particles are not.
Probably single-stranded. Molar percentages of nucleotides: G 16; A 22;
C 33; U 29. RNA is estimated to be c.
38% of particle weight; sedimentation
coefficient and molecular weight not determined.
Protein: 62% of particle weight; molecular weight and amino acid composition
Relations with Cells and Tissues
No intracellular inclusions detected by light microscopy.
Particles of cacao yellow mosaic,
turnip yellow mosaic
wild cucumber mosaic
viruses are similar in size, shape, external morphology and sedimentation velocity, and
contain similar amounts of nucleic acid of similar composition. Although beetles have not
yet been tested for their ability to transmit cacao yellow mosaic virus, its properties
and its distant serological relationship to the other two viruses indicate that it should
be grouped with beetle-transmitted viruses.
- Blencowe, Brunt, Kenten & Lovi, Trop. Agric. Trin. 40: 233, 1963.
- Brunt, Kenten, Gibbs & Nixon, J. gen. Microbiol. 38: 81, 1965.
- Gibbs, Hecht-Poinar, Woods & McKee, J. gen. Microbiol. 44: 177, 1966.
- MacLeod & Markham, Virology 19: 190, 1963.
Symptoms in a naturally infected West African Amelonado cacao leaf.
Systemically infected Amelonado leaf from a seedling grown from an inoculated
Circular necrotic lesions in an inoculated Chenopodium amaranticolor leaf.
Systemically infected C. amaranticolor leaf.
Purified virus preparation mounted in 2% neutral potassium phosphotungstate.
Bar represents 100 nm. (Micrograph courtesy R. D. Woods.)
Schlieren diagram produced by purified virus in the analytical ultracentrifuge
showing (left) 49 S and (right) 108 S components. (Photo courtesy
R. D. Woods.)