Fighting a Fungal Siege on Cacao
Pathogenic fungi that cause witches' broom on cacao tree limbs and trunks also
attack pods, destroying the valuable beans inside.
Americans love chocolate. Unfortunately, so do three pathogenic fungi that
attack cacao trees, Theobroma cacao. These trees produce the pods that
contain the beans used for making chocolate. The fungal infections lead to
diseases known as black pod rot, frosty pod rot, and witches'-broom.
Black pod rot is caused by Phytophthora species. They are cousins
to the fungi that cause pepper blight and late blight of potato. Probably about
five or more different species of soilborne Phytophthora cause the pod
rot disease that also attacks seedlings and causes cankers on stems, trunks,
and crowns that are actually the base of cacao trees.
Frosty pod rot, caused by Moniliophthora roreri, produces masses of
spores that appear as a white or tan powder on the pod's surface. The disease
distorts the pods; they become asymmetric or develop a mosaiclike pattern of
green, yellow, and cream. It rots the pod's interior and destroys the beans.
Witches'-broom is caused by Crinipellis perniciosa. This fungus
causes the tree to send up a spray of crazy shoots from its flower clusters and
branch tips and also infects the pods, making them unusable. Witches'-broom
severely reduces the ability of trees to produce pods filled with beans.
"All three fungi have caused severe yield losses to the 3-million-ton
annual cacao bean crop," says Eric M. Rosenquist. He is international
program coordinator for the Agricultural
Research Service's National Program Staff. "The fungi have inflicted
economic hardship on the 5 to 6 million small farmers in South America, Africa,
and Asia who produce and depend on the annual cash crop."
Where Cacao's a Top Crop
Brazil exports about $100 million in cacao beans to the United States
annually and has traditionally been the top South American cacao exporter.
But witches'-broomand other problemshave made Brazil slip to
eighth place in the past 5 years.
"In 1992, Bahia, Brazil, was the world's second biggest producer of
cacao," says John B. Lunde, director of international environmental
programs for M&M Mars, Inc., of Hackettstown, New Jersey, one of the
world's largest chocolate manufacturers.
"Harvest and export to the United States of Brazilian beans from Bahia
have plummeted from 430,000 tons in 1985-86 to about 130,000 tons today. The
major culprit is witches'-broom disease," says Lunde.
Martin Aitkin (left), director of the M&M Mars, Inc., Almirante Farm, and a
local farmer assess damage from a large, dry witches'-broom growth in a cacao
tree at the Luz de Maria farm in Uruçuca, Brazil.
M&M Mars and other importers of cacao beans are concerned that West
African countries, the current major exporters of cocoa, cannot handle alone
the world's growing appetite for chocolate. The Ivory Coast supplies about 50
percent of the cacao beans for the world. Such reliance could endanger the U.S.
supply of beans in cases of droughtwhich is not unusualpolitical
unrest, or high rates of infection with Phytophthora or other
To find a solution to cacao's fungal problems, Rosenquist went to ARS plant
pathologist Robert D. Lumsden at the ARS Biocontrol of Plant Diseases
Laboratory (BPDL) in Beltsville, Maryland.
Rosenquist says the lab is "uniquely suited to solving these problems.
Based on methods developed by ARS, biocontrol products are now being marketed
to control several pathogens of greenhouse, fruit, and vegetable crops."
"Not all these fungal pathogens are problems in all cacao-growing
regions," says Lumsden. "Current strategies available to control the
diseases include cultural practices such as pruning diseased trees and cleaning
up infected pods and branches; spraying with copper-based fungicides; and
breeding trees for resistance."
"Chemical controls for the fungi don't work very well and are
expensive," says M&M Mars microbiologist Prakash K. Hebbar, who is
working with Lumsden at Beltsville. "But," Hebbar notes,
"cultivars tolerant of the fungal diseases are largely unidentified or
have not been propagated in sufficient quantities."
"The ARS program represents a major step forward in cacao disease
research and brings important cutting-edge science, skills, and needed
technical leadership to a serious global problem that threatens the long-term
health of the chocolate industry," says Lunde.
"Eric Rosenquist's program is making an important and essential
difference. The program is also providing some needed hope to many small cacao
farmers facing financial ruin and to environmentalists concerned about the loss
of cacao agroforests."
Plant pathologist Robert Lumsden counts the fanlike basidiocarps (right)
produced by Crinipellis perniciosa mushrooms growing on dry
witches'-broom incubated in a humid chamber. He will collect fungal spores for
laboratory and greenhouse studies to identify prospective biocontrol agents.
Hebbar and Lumsden are part of a cooperative research project that includes
various national and international research institutes. Their goal is to
identify biological control strategies to be used in integrated pest management
(IPM) systems to fight these diseases.
Research strategies include combining environmentally compatible biological
control techniques with resistant cacao lines and using cultural practices that
encourage sustainable cacao cultivation in the natural forest ecosystem.
It Takes a Consortium
The international effort is funded by the U.S. Department of Agriculture,
coordinated by Rosenquist; the American Cocoa Research Institute (ACRI) in
McLean, Virginia; and M&M Mars, Inc.
Cooperators include ACRI; Comissião Executiva do Plano da Lavoura
Cacaueria (CEPLAC) in Itabuna, Brazil; CABI-Bioscience in Ascot, United
Kingdom; Servico Nacional de Sanidad Agraria of Lima, Peru; U.S. Agency for
International Development in Washington, D.C.; the Organization of American
States in Washington, D.C.; the Smithsonian Tropical Research Institute in
Panama City, Panama; Centro Agronómico Tropical de Investigación
y Enseñanza (CATIE) in Turrialba, Costa Rica; Pennsylvania State
University; and the University of Maryland's Wye Institute, Eastern Shore.
One of a few successes reported thus far came from a Brazilian scientist,
Cleber N. Bastos, of CEPLAC, and British scientist Harry C. Evans, of
CABI-Bioscience. They discovered a beneficial fungus, Cladobotryum
amazonense, with potential for use in biocontrol of witches'-broom.
Bastos also discovered a funguswhich he initially identified as
Trichoderma viridethat inhibits witches'-broom. He showed how
this species was effective in suppressing the witches'-broom pathogen under
laboratory conditions by actively parasitizing it.
Spores released from the fan-shaped basidiocarp of this inch-wide Crinipellis
perniciosa mushroom can infect cacao trees and drastically reduce yields of the
beans from which cocoa and chocolate products are made.
Hebbar asked ARS mycologist and Trichoderma expert Gary J. Samuels
at the Systematic Botany and Mycology Laboratory at Beltsville for help in
identifying the beneficial fungus.
Samuels' job is to describe and catalog new species of fungi for USDA's U.S.
National Fungus Collection, the world's largest herbarium of fungal
specimensabout 1 millionat Beltsville. His work lays the foundation
for other scientists who, like Lumsden, develop biological agents to combat
pathogenic fungi that destroy crops.
Also Out of the Amazon
Samuels says many biocontrol fungi belong to the genus Trichoderma.
Using both morphological and molecular characteristics, he discovered that the
fungus which parasitizes the witches'-broom fungus had been misnamed. Differing
from T. viride in its appearance and DNA characteristics, it was
renamed T. stromaticum.
"It's a new species of Trichoderma from the Amazon Basin of
Brazil," says Samuels. "Trichoderma is one of the most often
used biofungicides. In experiments, it has controlled other diseases caused by
Phytophthora species, the organism responsible for crown rot of apple
trees. It also controls various species of Pythium and
Rhizoctoniasoilborne fungi that cause damping-off diseases in
seedlings of agricultural and nursery crops."
"Commercial formulations of other Trichoderma species are the
fungi most often used as biofungicides," says Lumsden, "including
SoilGard, a form of Trichoderma (syn. Gliocladium)
virens developed by the BPDL."
In Uruçuca, Brazil, Martin Aitkin (right) of M&M Mars, Inc.,
discusses low bean yield with local farmers. Before widespread witches'-broom
problems, this 40-by-80-foot drying platform would have been covered with
harvested cacao beans.
Initial small-scale field and lab trials conducted in Brazil in
collaboration with J.L. Bezerra and J.B. Costa at the CEPLAC research center
showed that T. stromaticum could reduce formation of fruiting bodies,
or basidiocarps, of the witches'-broom fungus by 99 percent when brooms were in
contact with the soil, and by 56 percent in brooms remaining on trees. It
reduced pod infection by 31 percent.
To confirm these results, several labs in cacao-growing countries are
scaling up production of strains of biocontrol fungi, including T.
stromaticum, in collaboration with BPDL scientists. Large-scale field
trials are being performed in Bahia, Brazil, at CEPLAC and at M&M Mars'
Almirante Farm, Center for Cacao Studies; at the CABI-USDA Project in Huallaga
Valley, Peru; and at CATIE in Costa Rica.
Putting the Heat on Frosty Pod
"After frosty pod rot arrived in Peru in 1991," says Hebbar,
"cacao production fell from 1,236 tons in 1992 to 427 tons in 1993. Pod
yields of 520 pounds of beans per acre were well below the national average of
781 pounds per acre. Losses of up to 100 percent and the lack of economical
disease control led to neglect and abandonment of cacao fields. This made cacao
production even less profitable."
In January 1997, under the direction of CABI-Bioscience's Ulrike Krauss,
USDA and CABI-Bioscience started the biocontrol of cacao disease project in
Peru. For the first year of trials, the scientists used three abandoned fields
that were highly diseased. Flowers and pods of 20 trees per treatment were
sprayed monthly with a mixture of five strains of Trichoderma species.
"Results of these tests are very encouraging," says Hebbar.
"Frosty pod rot, the main disease in Peru, was reduced
significantlyby about 49 percent, under a wide range of growing
Biocontrol improved the number of healthy pods by about 62 percent in all
fields, though yields increased only in the shaded plots where disease was
controlled early. Yields were raised considerably more with a mixture of the
five biocontrol strains than with a single one.
Producers on small farms like Fazenda Santa Maria, near Uruçuca, are
searching for alternative crops that will enable them to survive if
cacao-destroying fungi cannot be curbed.
Still a Lot To Learn
Hebbar says that "biocontrol agents that are adapted to a variety of
conditions are being studied and should be tested. These organisms are from the
cacao environment and may perform best if combined into mixed sprays to cover
the entire range of conditions."
Initial results showed that to be most effective, biocontrol sprays must be
applied at the peak of flowering.
Cacao cultivation can be managed best under the shade of the tropical
rainforest. "Growing cacao trees under the rainforest shade canopy, or
cabruca, protects the trees and allows biocontrol sprays to last longer and
remain more effective," says Hebbar.
"The biocontrol fungal sprays were produced in one of two ways,"
he adds, "either as a preparation in sterilized liquid cultures or as a
solid substrate preparationboth composed of desiccation-resistant spores
of the fungi."
ARS scientists are investigating how the new Trichoderma species
works to control witches'-broom. Learning the mechanism of action may provide
clues for enhancing biocontrol activity. They are also trying to improve the
economical mass-production of the beneficial fungus.
"This would make it easier and more cost effective for small farmers to
use," says Hebbar. At the M&M Mars, Inc., Almirante Farm,
microbiologist Smilja Lambert oversees seven experiments involving monthly
spraying of new Trichoderma strains. Almost 12,000 cacao trees are
included in these trials.
At the M&M Mars, Inc., Almirante Farm facility, biologist Smilja Lambert
(left), microbiologist Prakash Hebbar (center), and agronomist Claudio Pinto
examine healthy pods on cacao cultivars resistant to witches'-broom
Results from harvesting pods showed that fewer pods per tree were infected
by witches'-broom when trees were treated with the Trichoderma strains
and prunedcompared with untreated and unpruned controls.
"We found that combinations of biocontrol agents were more effective
than a single strain," says Hebbar. "Time of application and shade
conditions are crucial for biocontrols to be effective. We will continue to
evaluate spore types of biocontrol agents for their efficacy."
With the exception of facilities at CEPLAC and the M&M Mars Almirante
Farm in Brazil, facilities to mass-produce biocontrol agents are currently
lacking in Latin America. Scientists in Peru are scaling up their facilities to
mass-produce the agents.
To better evaluate the disease-control potential of biocontrol agents
currently available and being used in small field trials, Hebbar says, "it
will help to have scaling-up fermentation and formulation facilities with
carefully monitored quality-control protocols."
Current facilities must be upgraded to mass-produce biocontrol agents. Then,
these agents must be tested as soon as possible at field sites with the
agricultural extension network and other agencies, says Hebbar.
Cooperative research agreements are currently in place to transfer
technology from ARS and CABI-Bioscience to scientists in Peru, Panama, and
Costa Rica to mass-produce biocontrol agents, test them under field conditions,
and improve methods of applying them.
"The emphasis will be on developing integrated pest management
strategies, as well as on mass-producing the agents themselves," says
The IPM technology to control cacao disease epidemics will be helped by a
cooperative project funded jointly by ARS, ACRI, and M&M Mars to predict
disease outbreaks and manage and protect natural resources, soil and water
ecology, and cacao genomics.
"Biocontrol is not a magic bullet that will suppress all three major
fungal diseases," says Hebbar. "Applying biocontrol sprays along with
pruning, proper plant nutrition, and use of disease-tolerant cultivars should
improve yields by lessening the incidence of disease."By
Hank Becker, Agricultural
Research Service Information Staff..
This research is part of Plant Diseases, an ARS National Program (#303)
described on the World Wide Web at
Robert D. Lumsden and
Prakash K. Hebbar are at the
USDA-ARS Biocontrol of
Plant Diseases Laboratory, Bldg. 011A, 10300 Baltimore Ave., Beltsville, MD
20705-2350; phone (301) 504-5872/7985, fax (301) 504-5968.
C h o c o l a t e
Delicious & Nutritious!
Not only does chocolate taste good, it may be a good source of
phytochemicals and essential micronutrients, too.
Recent Agricultural Research Service studies in cooperation with the
University of California, Davis, and M&M Mars, Inc., show chocolate
contains a variety of compounds that may contribute to cardiovascular health.
In addition to carbohydrates, fats, and protein, it contains several
micronutrients, including the minerals iron, potassium, and zinc, and is
especially rich in magnesium, copper, and manganese. Also present are B
vitaminsriboflavin and niacin.
Though relatively high in vegetable fat (50 to 55 percent), cocoa butter has
been shown to have no effect on blood cholesterol levels in humans. That's
because of its unique fatty acid composition, which is mainly stearic and oleic
acids. Cocoa is also packed with antioxidants that may help cut the risk of
developing cancer and heart disease.
Because of the emerging body of evidence that links phytonutrients and
long-term health, ARS has put together a world-class team of researchers led by
nutritionist Beverly A. Clevidence, who heads the Phytonutrients Laboratory in
Beltsville, Maryland. ARS and M&M Mars, Inc., are collaborating to better
understand the phytonutrient potential of chocolate and cocoa.
"Fighting a Fungal Siege on Cacao Farms" was published in
the November 1999 issue of
Agricultural Research magazine.