Cacao swollen shoot virus
A. A. Brunt
Glasshouse Crops Research Institute, Littlehampton, Sussex, England
- Theobroma virus 1 (Rev. appl Mycol. 27: 178)
- Marmor theobromae (Rev. appl. Mycol. 27: 178)
- Theobromavirus inflans (Rev. appl. Mycol. 38: 677)
A virus of great economic importance in West Africa, with numerous symptomatologically
distinct variants and a restricted host range; transmitted by 14 mealybug species, which
retain it for a few hours. Can be mechanically transmitted to cacao beans and has
bacilliform particles c. 121-130 x 28 nm.
In Theobroma cacao,
most strains induce conspicuous symptoms and reduce
yield, but are non-lethal unless subsequent attack by capsids debilitates trees further
and allows heavy infection with the die-back fungus Calonectria rigidiuscula
A few avirulent strains occur in limited widely scattered outbreaks,
usually induce stem swellings only, and have little effect, if any, on growth or yield.
Some virulent strains are widespread and lethal; in West African Amelonado cacao the
severe New Juaben strain induces conspicuous swellings in stems and tap roots
necrosis of lateral roots
defoliation, and the production of
small rounded mottled pods
containing fewer and smaller beans than normal
pods, a transient red vein-banding on young leaves and interveinal chlorotic speckling
and fern leaf patterns
on mature leaves
decreases yield by 25% within one year, 50%, within two years and usually kills trees
within 3-4 years
(Crowdy & Posnette, 1947
By contrast, Upper Amazon types of
cacao imported into West Africa in 1944 from Trinidad and Brazil, particularly those
originating from the Nanay
(Posnette & Todd, 1951
show resistance and tolerance to infection, intercrosses often producing highly
Widespread in West Africa (Ghana, Ivory Coast, Nigeria, Togo Republic and Sierra
Leone) and also occurs in Ceylon and possibly Sabah.
Host Range and Symptomatology
Experimental host range is limited to c.
30 species in the Bombacaceae,
Tiliaceae, Sterculiaceae and Malvaceae, some showing differential susceptibility to
(Posnette, Robertson & Todd, 1950
Tinsley & Wharton, 1958
Natural host range is restricted to cacao, Cola chlamydantha, Ceiba pentandra, Cola
(Posnette et al., 1950
(Legg & Agbodjan, 1969
- Theobroma cacao (cacao). Amelonado cacao is very susceptible
cacao beans being readily infected by viruliferous mealybugs
(Posnette & Strickland, 1948)
and by mechanical inoculation with concentrated virus preparations
(Brunt & Kenten, 1962);
seedlings usually produce acute red vein banding and chlorotic leaf
symptoms within 20-30 days and, 2-12 weeks later, swellings on shoots and tap roots
and interveinal leaf chlorosis characteristic of the particular strain
(Thresh & Tinsley, 1959).
- Corchorus spp. These are hypersensitive and quickly killed by most strains
(Tinsley & Wharton, 1958).
- Most other hosts remain symptomless; some strains, however, induce transient
chlorotic vein-banding leaf symptoms in Ceiba pentandra, Cola chlamydantha,
and Cola gigantea, and conspicuous, permanent leaf chlorosis and severe
stunting in Adansonia digitata
(Posnette et al., 1950).
- Cacao is a suitable plant for maintaining cultures; cacao, Adansonia digitata
and Bombax brevicuspe are convenient sources of virus for purification.
- Cacao: by recording the proportion of inoculated Amelonado cacao beans producing
Many distinct variants can be recognized; at one time they were named alphabetically
but now, as originally
they are usually named from the locality of
their origin. The best known is the severe New Juaben strain (strain A; Theobroma
virus 1A) which is widespread in the eastern region of Ghana (see Main Diseases).
The characteristic features of other well known strains occurring in Ghana (e.g. Bisa,
Bosomuoso, Bosumtwe, Mampong, mild New Juaben and Nkawkaw), Nigeria (e.g. Balogun,
Ilesha, Elepo and Offa Igbo), Ivory Coast (e.g. Kongodia and Sankadiokro) and Ceylon
have been summarized by
Thresh & Tinsley (1959)
Attafuah, Blencowe & Brunt (1963)
describe those of a strain from Sierra Leone.
Transmission by Vectors
Transmissible by at least 14 mealybug species (Hemiptera: Coccidae).
is often the most important, although in Nigeria
P. njalensis, Planococcus kenyae
and Planococcus citri
equally abundant. Nymphs (1st, 2nd and 3rd instars) and female adults are equally
efficient vectors but male adults are unable to transmit. A pre-acquisition starvation
period slightly increases vector efficiency, perhaps because it induces the insects
to settle more quickly. The minimum acquisition feeding period is 20 min and the
optimum, for long thought to be c.
(Posnette & Robertson, 1950
is probably 2-4 days
There is no detectable latent period; insects
may transmit within 15 min, but maximum transmission occurs after 2-10 hr
(Posnette & Robertson, 1950
The virus persists in feeding insects for 3 hr or
(Posnette & Strickland, 1948
but starved adults and 1st instar nymphs can
retain virus for 49 and 24 hr respectively
No transmission occurs
Vector specificity: Ferrisia virgata has transmitted all isolates tested
except that from Mampong which, like cacao mottle leaf virus, is transmitted
specifically by Pseudococcus longispinus
Transmission through Seed
The New Juaben and Bisa strains are not seed-borne
Transmission by Dodder
Not transmitted by Cuscuta chinensis
(Posnette et al., 1950
Antisera with titres of 1/128 have been prepared against strains from New Juaben,
Mampong and Anibil; the low titres are probably due to the relatively low virus content
of the preparations used for immunization. Gel-diffusion serological tests distinguish
specific reactions from those attributable to host protein contaminants (Kenten &
The three strains tested show some antigenic differences, but are related to each
other and to
cacao mottle leaf virus
(Kenten & Legg, unpublished).
Stability in Sap
Crude saps are non-infective but extracts made with antioxidants sometimes infect
up to 5% of inoculated cacao beans
(Brunt & Kenten, 1962
using concentrated virus
preparations, transmission rates from 60 to 90% are obtained. In partially purified
preparations, the thermal inactivation point (10 min) is c.
and infectivity is retained without appreciable
loss for 2-3 months at 2°C
(Brunt, Kenten & Nixon, 1964
Kenten & Legg, 1965
Difficulties due to mucilaginous and polyphenolic material are overcome by extracting
cacao leaves in ten to twenty times their weight of 0.05 M phosphate buffer at pH
6.0-8.0 containing added protein (1-2% w/v egg albumin, bovine serum albumin or,
preferably, hide powder) in addition to either 0.05 M thioglycollate or 0.01-0.005 M
(Brunt & Kenten, 1963
Virus can then be sedimented by one
or more cycles of differential centrifugation, or by ultracentrifugation (75,000
for 1 hr) following a preliminary concentration by precipitation with
(Kenten & Legg, 1965
Properties of Particles
Sedimentation coefficient (s20,w
) at infinite dilution of Mampong
strain: 218 S.
Particles are bacilliform
about 121-130 x 28nm, with no discernible
substructure when mounted in neutral 2% potassium phosphotungstate
(Brunt et al., 1964
Kenten & Legg, unpublished). Empty square-ended tubular particles present
in some preparations are probably degraded bacilliform particles
(Kenten & Legg, 1967
Relations with Cells and Tissues
Tissues in chlorotic areas of leaves remain undifferentiated, contain small
flattened chloroplasts and have reduced intercellular spaces; secondary xylem and
phloem are both increased in stem and root swellings, but no phloem necrosis occurs
(Knight & Tinsley, 1958
Cacao swollen shoot and
cacao mottle leaf viruses
are both transmitted by mealybugs
have similar particles and properties
(Brunt et al., 1964
Kenten & Legg, 1967
and are now known to be serologically distantly related
(Kenten & Legg, personal communication). It is uncertain, therefore, whether
cacao mottle leaf virus should be considered a distinct virus or a serotype of cacao
swollen shoot virus.
Two distinct virus strains transmissible by mealybugs infect cacao in Trinidad and
another mealybug-transmitted virus infects pineapple in Hawaii
is known about these and the viruses reported to infect cacao in Java, Colombia,
Dominican Republic and Venezuela
(Thresh & Tinsley, 1959)
so that comparisons with
cacao swollen shoot and mottle leaf viruses are not possible.
- Attafuah, Blencowe & Brunt, Trop. Agric. Trin. 40: 229, 1963.
- Brunt & Kenten, Ann. appl. Biol. 50: 749, 1962.
- Brunt & Kenten, Virology 19: 388, 1963.
- Brunt, Kenten & Nixon, J. gen. Microbiol. 36: 303, 1964.
- Carter, Ann. N.Y. Acad. Sci. 105: 741, 1963.
- Crowdy & Posnette, Ann. appl. Biol. 34: 403, 1947.
- Dale, Rep. W. Afr. Cocoa Res. Inst. 1954-55: 33, 1955.
- Dale, Rep. W. Afr. Cocoa Res. Inst. 1955-56: 35, 1957.
- Kenten & Legg, Ghana J. Sci. 5: 221, 1965.
- Kenten & Legg, J. gen. Virol. 1: 467, 1967.
- Knight & Tinsley, Ann. appl. Biol. 46: 7, 1958.
- Legg & Agbodjan, Rep. Cocoa Res. Inst. Ghana 1967-68: 25, 1969.
- Lister, Rep. W. Afr. Cocoa Res. Inst. 1952-53: 9, 1953.
- Posnette, Ann. appl. Biol. 34: 388, 1947.
- Posnette, Ann. appl. Biol. 37: 378, 1950.
- Posnette & Robertson, Ann. appl. Biol. 37: 363, 1950.
- Posnette & Strickland, Ann. appl. Biol. 35: 53, 1948.
- Posnette & Todd, Ann. appl. Biol. 38: 785, 1951.
- Posnette, Robertson & Todd, Ann. appl. Biol. 37: 229, 1950.
- Roivainen, Rep. Cocoa Res. Inst. Ghana 1967-68: 40, 1969.
- Thresh, Emp. J. exp. Agric. 28: 193, 1960.
- Thresh & Tinsley, Tech. Bull. W. Aft. Cocoa Res. Inst. 7: 32 pp., 1959.
- Tinsley & Wharton, Ann. appl. Biol. 46: 1, 1958.
West African Amelonado cacao leaf with interveinal chlorosis induced by the
severe New Juaben strain. (Photo courtesy A. F. Posnette.)
Chlorotic vein banding (fern leaf patterns) on mature Amelonado leaf
infected with the New Juaben strain. (Photo courtesy A. F. Posnette.)
Stem swelling on naturally infected Amelonado tree. (Photo courtesy R. H.
Root systems from 6-week-old seedlings; (left) healthy, (right)
infected with the severe New Juaben strain.
Virus particles from a partially purified preparation of the strain from Anibil,
Ghana; mounted in 2% neutral potassium phosphotungstate. Bar represents 100 nm. (Photo
courtesy R. D. Woods.)
(Left) small, rounded pod from severely affected tree, (right)
normal pod. (Photo courtesy A. F. Posnette.)