The coffee is part of Rubiaceae which include some 500 genera and over 6000 species. Most are tropical trees and shrubs that grow in the lower floors of the forest. The family also includes the gardenias and plants which produce quinine and other useful substances, but Coffea is by far the family member’s most important economically.

Since Coffea was described by Linnaeus in the mid-18th century, botanists bicker 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 cover small shrubs and tall trees over 10 meters, the leaves may be yellow, dark green, bronze or purple.

The two species of coffee’s most important economically are Coffea arabica (Arabica coffee) – which represents over 70% of world production – and Coffea canephora (Robusta coffee). Two other species are grown at a smaller scale: liberica Coffea (coffee Liberica) and dewevrei Coffea (coffee Excelsa).

 

Coffea arabica – Arabica coffee

Coffea arabica was first described in 1753 by Linnaeus. The best known varieties are ‘Typica’ and ‘Bourbon’ that gave rise to many strains and cultivars such as multiple Caturra (Brazil, Colombia), Mundo Novo (Brazil), Tico (Central America), the dwarf San Ramon and Jamaican Blue Mountain. Arabica coffee is usually a large shrub with dark green oval leaves. It is genetically different from other coffee species because it has four chromosomes instead of two. Its fruits are oval and mature in 7-9 months they usually contain two flat seeds (coffee 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 a major goal 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 grown variety of this species. It is a shrub or small tree up to a robust 10 meters high, with shallow roots. Its fruits are round and can take 11 months to mature and the seeds are oval and smaller than those of C. arabica. Robusta coffee is grown in West Africa and Central Asia year South East and, to some extent in Brazil under the name Conillon.

 

Liberica Coffea – Coffee Liberica

The coffee plant is a large tree Liberica robust up to a height of 18 meters, with large leaves rubbery. Its fruits 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 flavor characteristics is low.

Plant Selection


Coffea arabica

C. Arabica is a tetraploid (44 chromosomes) autogamous. 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 colony on the island of Bourbon (now Réunion). C. Arabica is autogamous, these varieties have remained genetically stable. However, spontaneous mutations exhibiting desirable characteristics have been cultivated and exploited crossing. Some of these mutants and cultivars are described below.

Mutants: Caturra – compact form of the Bourbon Maragogype – mutant typica with grains elephants. San Ramon – Purpurascens dwarf typica – purple leaves

Cultivars have been developed to obtain maximum economic return under 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
– Novo Mundo – the intersection of Bourbon and Typica, originally grown in Brazil
– Kent – originally developed in India, with some disease resistance
– Catuai-hybrid Mundo Novo and Caturra, characterized by yellow or red cherries: Catuai amarelo-and-Catuai vermelho respectively.

 

Coffea canephora

C. canephora is a diploid self-sterile producing many forms and wild varieties. The identification of cultivars is unclear but both forms are recognized:

“Robusta” – to erect
“Nganda” – trailing growth habit

Hybrids of Arabica and Robusta

Coffee trees were selected to improve the following characteristics: growth and flowering, yield, size and shape of grains, quality tasting, caffeine content, disease resistance, drought resistance.

Crosses of Arabica and Robusta Arabica seek to improve by giving it force and resistance to disease and improve the quality of the tasting Robusta.

Hibrido Timor is a natural hybrid of arabica x robusta which resembles arabica and 44 chromosomes.

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

A new dwarf hybrid called Ruiru 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 performance and supports a planting density twice normal.

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

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

 

Selection techniques

1. Pollination and seed multiplication controlled by two. Vegetative propagation (clonal)

Conventional methods: grafting, cuttings

New methods (tissue culture): micropropagation, somatic embryogenesis

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

 

References

Clifford M.N. and Willson K.C. (Editors) – Coffee; botany, biochemistry and production of beans and beverage. Londres, Croom Helm, 1985
Wrigley G. – Coffee. Londres, Longman, 1988