Plant Pathology in an International Context

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• Plant Pathology in an International Context
• Diversity of international agriculture
• What is unique about tropical plant pathology?
• Colonial cash crop agriculture costly lessons

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There is not one international plant pathology
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Maize in South Africa
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Poinsettias grown in Guatemala for export 700
workers, ship 1.5 million cuttings/day
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Bedding plants grown for export in Guatemala
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Rice, the worlds most important crop, grown in
paddies or upland from Asia to Africa
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• There is not one international plant pathology
• -Intensively managed high-yield wheat grown in
  Germany
• Hothouse fresh market cucumbers in Algeria
• Ornamental bedding plants for export from
  Guatemala
• Mixed corn and beans grown for subsistence in
  Central America
• Paddy rice grown 3 seasons/year in the
  Philippines
• Cassava grown as a carbohydrate subsistence crop
  in West Africaetc etc

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What is Unique About Tropical Plant
Pathology? SOILS Tropical soils often thin and
nutrient-poor nutrients are tied up in
biological materials SEASONS No winter, so pest
populations can remain high year-round SOCIAL/ECO
NOMIC FORCES drive towards large-scale export
cash crops, with small-scale subsistence or
market farming wedged into marginal land
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Top 10 Global Crops (commercial, by
weight) Sugar Cane Maize Wheat Rice Potato S
ugar Beet Soybean Oil Palm Fruit Barley
Tomato
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Major Global Subsistence Crops Cassava Rice Plant
ains Corn (maize) Beans Tef Millet Potatoes Palm
hearts Sorghum Peanut, Mango, Papaya, etc.
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Often little attention is given to pest problems
of non-commercial subsistence crops in the
developing tropics -no industrial
interest -universities under-resourced and lack
expertise -experts in the developed world unaware
or uninterested (no funding, little baseline
data, logistical difficulties) -NGOs like the
CGIAR centers work on these problems, but have
limited resources
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Disease control in the developing tropics Often
weakly regulated Serious environmental and human
health threats
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Black Sigatoka Disease Mycosphaerella fijiensis
Panama Wilt Disease Fusarium oxysporum f. sp.
cubanense
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Cassava (manioc) major source of carbohydrates
in Africa and S. America
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Cassava mosaic virus symptoms
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Oil Palm- largest global source of food oil
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Sudden wither of oil palm- Possibly Phytomonas
(phytoplasma bacterium)?
Fatal yellowing of oil palm- cause unknown
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Palm oil plantation with forest burning in
background
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Costly Lessons from Colonial/Industrial Cash Crop
Agriculture Coffee Rust
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Coffee

• Grown in 50 countries, all in the tropics
• Produced by an estimated 25 million farmers
• 2nd most valuable commodity of developing
  countries, after oil.
• Global production is estimated at 60 billion
  annually
• Global production in 2002/2003 was approximately
  16.1 billion lbs.

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The Coffee Tree Coffea arabica or Coffea
canephora
Needs warm days cool nights Cannot tolerate
freezing
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Coffee Rust Originally described in 1869 by
Rev.Berkeley and Mr Broome, as a mycological
curiosity By 1875 no plantation on the island
was free of the disease Production dropped from
100M lb/yr in 1870 to 5M lb/yr in 1890 Monetary
losses of 200 million British pounds per year
Economy of Sri Lanka in ruins - social unrest
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Coffee Rust-Hemileia vastatrix
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Coffee Rust caused by Hemileia vastatrix
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www.apsnet.org
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Shade-grown vs. sun-tolerant coffee production
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South American Leaf Blight of Rubber caused by
Microcyclus ulei
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Black pod of cacao caused by Phytophthora
palmivora
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Black pod of cacao caused by Phytophthora
palmivora
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Witches Broom caused by Crinipellis perniciosa
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Witches Broom caused by Crinipellis perniciosa
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Integrated rice and duck farming - Furuna
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Lessons 1. Genetic vulnerability - all coffee
descended from 1 tree, large acreages of same
genotype - very vulnerable. NO variety at all.
Not like native situation in Ethiopian forests
where spore has few chances to find a host, hosts
have varying levels of resistance. 2. Shift in
areas where coffee is grown - went to Latin
America to avoid disease, changed many
economies 3. Once it appeared in L.A., cultural
practices had to change - no more shade, loss of
overstory tree diversity 4. Fungicide now
continuously applied - environmental
contamination problems (e.g soil-contaminating
lead arsenate re-legalized in Costa Rica for rust
control)
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Coffee Rust Disease

• Occurs mainly on leaves but can also develop on
  fruits, buds, and stems
• Recognized by yellow to orange lesions on the
  abaxial (underside) of leaves.
• Lesions are typically concentrated at the leaf
  margin and develop through the canopy from the
  bottom up
• Unlike many rusts, sporulation occurs through
  the stomata and not through the rupturing of the
  epidermis
• Leads to premature leaf drop and eventual
  defoliation, death of the tree

Coffee Rust
www.apsnet.org
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Coffee originated in Ethiopia long used by
native peoples who chewed the leaves and made a
paste of the green beans, which they ground
mixed with honey. Around 200 BC, Persians
conquered area, searched for spices stimulants
found coffee began to trade it Around 550 AD,
first record of planting coffee in Yemen (Arabia)
in oases. Port of Mokka in Yemen was main source
of coffee all of Europe depended on this source.
Arabs would not allow export of unroasted
(fertile) beans wanted to maintain control of
coffee market. Was an extremely expensive luxury.
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In 1616, Dutch brought a few trees from India -
multiplied them by cuttings in greenhouses One
tree sent as a gift by Dutch to Louis 16th of
France, who had it propagated sent to the
French colonies (descendents of this tree are
known as "Bourbon" variety since Louis was a
member of the Bourbon dynasty). French trees
were sent to Martinique by boat with Chevalier de
Clieu boat hit the doldrums ran low on fresh
water. de Clieu gave his drinking water ration
to one tree, which survived was parent to all
trees in French W. Indies, Latin
America. Brazilians obtained some of these trees
when de Melhu, the Brazilian ambassador to French
Guyana (central America), seduced wife of a
government official persuaded her to help him
steal coffee seedlings. British eventually got
one of these.
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So very narrow genetic base in colonial coffee
plantations even though back in Ethiopia there
are several different species C. canephora, C.
robusta - although these have different, less
desirable flavor. In 1700's coffee consumption
increased dramatically in Europe N. America -
coffeehouses very popular Ceylon (Sri Lanka) was
by then a British colony heavily planted to
coffee, became leading producer in the world.
Nearly the whole island cleared of jungle
planted to coffee -railroad built to transport
coffee beans, -Thousands of Tamil people from
S. India imported to labor on the coffee
plantations, setting the stage for ethnic strife
btwn Tamils native Sinhalese people that
continues to present.
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Following the disaster in Sri Lanka, coffee
production shifted to Latin America, which
remained disease-free (under quarantines) until
1970 - but then coffee rust appeared spread
quickly. First in Bahia in Brazil, then
Paraguay, Peru, Venezuela, then Nicaragua, now
all over Central America. Not the disaster it
would have been 50 years ago because of modern
fungicides - but it has changed coffee
agriculture throughout Latin America.
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1. Must apply rust controlling fungicides by air,
so... 2. Cultural practices had to be changed -
no more growing under shade, had to use
sun-tolerant dwarf "Caturra" coffee, considered
less desirable ("trash coffee"), needs more
chemical input. Loss of shade cover trees loss
of critical rainforest diversity, bird animal
habitat -More than 1/3 of all migratory birds
that breed in US spend the winter in Latin
America - Over the last 20 years, many bird
populations have declined, due in part to habitat
loss. -In the last 40 years, 2/3 of rainforest
in Central America has been lost to pasture,
sugar cane, rice, bananas. -Traditional shaded
coffee plantations provide some of the last
habitat in Central America for migratory birds
other wildlife, plants.
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(a) Soil amendment practice with poultry refuse
and mustard oil-cake in eggplant and cabbage for
disease control (b) IPM practice in cabbage for
controlling leaf-eating insects (c) Fruit and
shoot borer control in eggplant by using
pest-resistant varieties (d) Eggplant grafting
for bacterial wilt disease control (e) Fruit fly
control in sweet gourd by bait trapping (f) IPM
package for fruit and shoot borer control in
eggplant and (g) Tomato production by using
improved tomato varieties. The scientists and
the participator farmers explained the trials and
demonstrations and clarified the questions asked
by the Honble Minister or/and the participants.
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