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TYPES OF COFFEE (BOTANY):
Plant breeding Coffee belongs to the botanical family
Rubiaceae, which has some 500 genera and over 6,000 species. Most are
tropical trees and shrubs which grow in the lower storey of forests. Other
members of the family include the gardenias and plants which yield quinine
and other useful substances, but Coffea is by far the most important member
of the family economically.
FAMILY
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GENUS
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SPECIES: many
including
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VARIETIES
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Rubiaceae
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Coffea
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Arabica
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Typica
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-
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-
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Canephora
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Robusta
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-
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-
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Liberica
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-
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Since Linnaeus first correctly described Coffea, in the mid 18th century,
botanists have failed to agree on a precise classification system. There
are probably at least 25 major species, all indigenous to tropical Africa
and certain islands in the Indian Ocean, notably Madagascar. Difficulties in
classification and even in designation of a plant as a true member of the
Coffea genus arise because of the great variation in the plants and seeds.
All species of Coffea are woody, but they range from small shrubs to large
trees over 10 metres tall; the leaves can be yellowish, dark green, bronze
or tinged with purple. The two most important species of coffee
economically are Coffea arabica (Arabica coffee) - which accounts for over
70% of world production - and Coffea canephora (Robusta coffee). Two other
species which are grown on a much smaller scale are Coffea liberica (Liberica
coffee) and Coffea dewevrei (Excelsa coffee). Some differences between
Arabica and Robusta coffee
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Arabica
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Robusta
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Date species
described
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1753
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1895
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Chromosomes (2n)
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44
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22
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Time from flower
to ripe cherry
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9 months
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10-11 months
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Flowering
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after rain
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irregular
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Ripe cherries
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fall
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stay
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Yield (kg
beans/ha)
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1500-3000
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2300-4000
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Root system
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deep
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shallow
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Optimum
temperature (yearly average)
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15-24°C
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24-30°C
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Optimal rainfall
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1500-2000 mm
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2000-3000 mm
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Growth optimum
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1000-2000 m
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0-700 m
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Hemileia
vastatrix
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susceptible
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resistant
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Koleroga
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susceptible
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tolerant
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Nematodes
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susceptible
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resistant
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Coffea
arabica - Arabica coffee
Coffea arabica was first described by Linnaeus in 1753.
The best known varieties are 'Typica' and 'Bourbon' but from these many
different strains and cultivars have been developed, such as caturra (Brazil, Colombia),
Mundo Novo (Brazil),
Tico (Central America), the dwarf San Ramon and the Jamaican Blue
Mountain. The average
arabica plant is a large bush with dark-green oval leaves. It is
genetically different from other coffee species, having four sets of
chromosomes rather than two. The fruits are oval and mature in 7 to 9
months; they usually contain two flat seeds (the coffee beans) - when only
one bean develops it is called a peaberry. Arabica coffee is often
susceptible to attack by pests and diseases, therefore resistance is a
major goal of plant breeding programmes. Arabica coffee is grown throughout
Latin America, in Central and East Africa, in India
and to some extent in Indonesia.
The term 'robusta' is actually the name of a widely grown
variety of this species. It is a robust shrub or small tree growing up to
10 metres in height, but with a shallow root system. The fruits are rounded
and take up to 11 months to mature; the seeds are oval in shape and smaller
than those of C. arabica. Robusta coffee is grown in West and Central
Africa, throughout South-East Asia and to some extent in Brazil,
where it is known as Conillon.
Liberica coffee grows as a large strong tree, up to 18
metres in height, with large leathery leaves. The fruits and seeds (beans)
are also large. Liberica coffee is grown in Malaysia
and in West Africa, but only very small
quantities are traded as demand for its flavour characteristics is low.
Standard referencesClifford M.N. and Willson K.C. (Editors) -
Coffee; botany, biochemistry and production of beans and beverage. London, Croom Helm,
1985 Wrigley G. - Coffee. London,
Longman, 1988
C. arabica is a tetraploid (44 chromosomes) and is
self-pollinating. There are two distinct botanical varieties: arabica
(typica) and bourbon. Historically, typica was cultivated in Latin America
and Asia, whereas bourbon arrived in South America and, later, East Africa
via the French colony of Bourbon (Reunion).
Because C. arabica is self-pollinating, these varieties tended to remain
genetically stable. However, spontaneous mutations showing desirable
characteristics have been cultivated in their own right, as well as being
exploited for cross-breeding purposes. Some of these mutants and cultivars
are described below.
Mutants: Caturra - a compact form of bourbon Maragogipe - a mutant
typica with large beans San Ramon - a dwarf typica
Purpurascens - purple leaved forms Cultivars have been developed to
give the maximum economic return under specific regional conditions such as
climate, soil, methods of cultivation and the prevalence of pests and
diseases. Some of the better known cultivars are:
Blue Mountain - grown in Jamaica and Kenya
Mundo Novo - a cross between typica and bourbon, originally grown in
Brazil
Kent - originally developed in India, showing some disease
resistance
Catuai - developed as a hybrid of Mundo Novo and Caturra,
characterized by either yellow or red cherries:
Catuai-amarelo and
Catuai-vermelho respectively.
Coffea canephora
Canephora is diploid and self-sterile, producing many
different forms and varieties in the wild. The identification of cultivars
is confused, but two main forms are recognised: 'Robusta' - upright forms
'Nganda' - spreading forms
Arabica / robusta hybridsCoffee has been selectively bred to improve
characteristics of: growth and flowering, yield, bean size and shape, cup
quality, caffeine content, disease resistance, drought resistance. Crosses
between arabica and robusta aim to improve arabica by confering disease
resistance and vigour or to improve on the cup quality of robusta. Hibrido
de Timor is a natural hybrid of arabica x robusta which resembles arabica
coffee and has 44 chromosomes. Catimor is a cross between Caturra
and Hibrido de Timor and is resistant to coffee leaf rust (Hemileia
vastatrix). A new dwarf hybrid called Ruiru Eleven, developed at the Coffee
Research Station at Ruiru in Kenya, was launched in 1985.
Ruiru 11 is resistant to coffee berry disease and to coffee leaf rust. It is
also high yielding and suitable for planting at twice the normal density.
Icatu hybrids are the result of repeated backcrossing of interspecific
arabica x robusta hybrids to arabica cultivars Mundo Novo and Caturra.
Arabusta hybrids are fertile interspecific Fl hybrids from crosses between
arabica and induced auto-tetraploid robusta coffee. Techniques used in
coffee breeding Controlled pollination and multiplication by seed
Vegetative (clonal) propagation Traditional methods: grafting, taking
cuttings New methods (tissue culture): micropropagation, somatic
embryogenesis In recent years the potential of genetic manipulation of
Coffea using recombinant DNA technology and tissue culture techniques has
been investigated. By introducing new genes for characteristics such as
resistance to pests or to herbicides, or genes coding for desirable cup
quality attributes, it may be possible to produce plants with any
combination of features required. Standard references Clifford M.N. and
Willson K.C. (Editors) - Coffee; botany, biochemistry and production of
beans and beverage. London,
Croom Helm, 1985 Wrigley G. - Coffee. London,
Longman, 1988
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