Botanical aspects

Coffee is one of Rubiaceae which include some 500 genera and over 6000 species. Most are tropical trees and shrubs that grow in the lower forest floors. The family also includes the gardenias and plants which produce quinine and other useful substances, but Coffea is by far the member of the largest family economically. Since Coffea was described by Linnaeus in the mid 18th century, botanists squabble on a specific classification system. There are probably at least 25 major species, all native to tropical Africa and certain islands in the Indian Ocean, including Madagascar. The difficulties of classification and designation of a plant as a member of the genus Coffea are due to the wide variety of plants and seeds. All species of Coffea are woody, but they represent a small shrubs and large trees over 10 meters; leaves may be yellow, dark green, bronze or purple.
The two most economically important species of coffee tree view are Coffea arabica (Arabica coffee) - which represents over 70% of world production - and Coffea canephora (Robusta coffee). Two other species are grown on a smaller scale: Coffea liberica (Liberica coffee) and Coffea dewevrei (Excelsa coffee).

Differences between Arabica and Robusta

Arabica Robusta
Date description of the species 1753 1895
Chromosomes (2n) 44 22
Time between flowering and ripe cherry 9 months 10-11 months
Yield (kg grain / ha) 1500-3000 2300-4000
Roots deep shallow

Optimum temperature (annual average)

15-24 ° C 24-30 ° C
Optimal precipitation 1500-2000 mm 2000-3000 mm
Optimum altitude 1000-2000 m 0-700 m
Hemileia vastatrix sensitive resistant
Koleroga sensitive tolerant
Nematodes sensitive resistant
CWD resistant sensitive
Berry sensitive resistant
Caffeine content of grains 0.8-1.4% 1.7 to 4%
Grain Shape flat oval
Characteristic taste acidity bitterness, roundness
Body average 1.2% average 2%

Coffea arabica - Arabica coffee
Coffea arabica was described for the first time in 1753 by Linnaeus. The best known varieties are 'Typica' and 'Bourbon' which gave birth to many strains and multiple cultivars such as caturra (Brazil, Colombia), Mundo Novo (Brazil), Tico (Central America), the dwarf San Ramon and Jamaican Blue Mountain. The regular Arabica coffee is a large shrub with dark green oval leaves. It is genetically different from other species of coffee as it has four instead of two chromosomes. Its fruits are oval and mature in 7-9 months; they usually contain two flat seeds (beans) - when the cherry contains only one seed it is called caracoli or pearl. Arabica coffee is often susceptible to pests and diseases, and resistance is one of the main objectives of plant breeding programs. Arabica coffee is grown throughout Latin America, Central and East Africa, India and, to some extent, Indonesia.

Coffea canephora - Robusta coffee
The term "Robusta" is a widely cultivated variety of the species. It is a shrub or small sturdy tree can reach a height of 10 meters, with shallow roots. Its fruits are round and can take 11 months to mature; seeds are oval and smaller than those of C arabica form. Robusta coffee is grown in West Africa and Central Africa, Southeast Asia year, and, to some extent, in Brazil as the Conillon.

Coffea liberica - coffee Liberica
The coffee Liberica is a big strong tree can reach a height of 18 meters, with large rubbery leaves. Fruit and seeds (grains) are also big. Liberica coffee is grown in Malaysia and West Africa but only very small quantities are traded as demand for its characteristic flavor is low.

References
Clifford MN and Willson KC (Editors) - Coffee; botany, biochemistry and Production of beans and beverage. London, Croom Helm, 1985
Wrigley G. - Coffee. London, Longman, 1988


Plant selection

Coffea arabica
C. arabica is tetraploid (44 chromosomes) self-pollinating. There are two distinct botanical varieties: Arabica (typica) and Bourbon. Historically, typica was cultivated in Latin America and Asia while Bourbon arrived in South America and later in East Africa through the French settlement on the island of Bourbon (now Reunion). C. arabica is self-pollinating, these varieties have remained genetically stable. However, spontaneous mutations exhibiting desirable characteristics have been grown and harvested for the purpose of crossing. Some of these mutants and cultivars are described below.
Mutants: Caturra - compact form of Bourbon Maragogype - mutant typica with elephants grains. San Ramon - typica Purpurascens dwarf - purple leaf cultivars have been developed to achieve maximum economic efficiency in specific regional conditions of climate, soil, cultivation methods and prevalence of pests and diseases. The most popular cultivars are:

  • Blue Mountain - grown in Jamaica and Kenya
  • Mundo Novo - crossing Typica and Bourbon, originally grown in Brazil
  • Kent - originally developed in India, with some disease resistance
  • Catuai -hybride Mundo Novo and Caturra, characterized by yellow or red cherries: Catuai-vermelho-amarelo and Catuai respectively.

Coffea canephora
C. canephora is a self-sterile diploid that produces many shapes and wild varieties. The identification of cultivars is unclear but two forms are recognized:

  • 'Robusta' -, erect
  • "Nganda" - to creeping

Hybrid Arabica and Robusta
Coffee trees were selected to improve the following: growth and flowering, yield, size and shape of grains, quality tasting, caffeine content, disease resistance, drought resistance. Crosses Arabica and Robusta Arabica looking to improve by giving it resistance to disease and effect and to improve the quality tasting Robusta.
Hibrido Timor is a natural hybrid Arabica Robusta x resembling Arabica and 44 chromosomes.

Catimor is a cross between Caturra and Hibrido Timor; it is resistant to leaf rust (Hemileia vastatrix).

A new hybrid called Ruiru dwarf Eleven, developed at the Research Station Coffee Ruiru (Kenya), was launched in 1985 Ruiru 11 is resistant to coffee berry disease and leaf rust. It has a high efficiency and a planting density support twice the normal.

Hybrid Icatu are the result of repeated backcrossing of interspecific hybrids x Arabica Robusta and Arabica cultivars Mundo Novo and Caturra.

Hybrid Arabusta are fertile interspecific hybrids Fl resulting from crosses between Arabica and Robusta induced autotetraploid.

 

Selection techniques
  1. Pollination and seed multiplication by controlled
  2. Vegetative propagation (clonal)
  • Conventional methods: grafts, cuttings
  • New methods (tissue culture): micropropagation, somatic embryogenesis

In recent years, we investigated the potential of genetic engineering Coffea using the technique of recombinant DNA techniques and tissue culture. By introducing new genes for resistance to pests or herbicides, or genes conferring qualities tasting cup, it might be possible to produce plant material comprising all the desired characteristics.

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References
Clifford MN and Willson KC (Editors) - Coffee; botany, biochemistry and Production of beans and beverage. London, Croom Helm, 1985
Wrigley G. - Coffee. London, Longman, 1988

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Text from the world of coffee
Source: French Committee of coffee
http://www.comitefrancaisducafe.fr/

 

 

 

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