Coffea arabica L.

Coffea arabica is an evergreen, shrub or small tree, up to 5 m tall when unpruned, glabrous, with small glossy leaves. Leaves are simple, alternate, opposite, thin, dark-green, shiny surfaced, fairly stiff; axillary and sub-axillary buds often develop into reproductive lateral branches. Leaves petiolate, sometimes bearing interpetiolar stipules. Prominent leaf midrib and lateral veins. Flowers produced in dense clusters along reproductive branches in the axils of the leaves. White, sweet scented, star-shaped and carried on stout but short peduncles. Bracteoles united, forming a cup-shaped epicalyx at the base of the flower. There are 5 calyx segments halfway the length, spreading out very widely at the anthesis and 5 stamens inserted in the corolla tube. Anthers carried on long, slender, upright filaments. Ovary inferior, 2 united unilocular carpels, each containing a single ovule attached to the base of the carpel wall. The ovary bears a slender style, which terminates in short, pointed bifid stigmas. Fruit a drupe; pericarp composed of shiny exocarp, fleshy mesocarp and relatively thin but tough endocarp, in which the seeds are enclosed. Immature berries dull green; on ripening the skin colour changes through yellow to bright crimson. Each berry contains 2 seeds, 8.5-12.5 mm long, ellipsoidal in shape and pressed together by flattened surface that is deeply grooved; outer surface convex. Thin, silvery testa follows outline of endosperm, so fragments are often found in ventral groove after preparation. Seeds consist mainly of green corneous endosperm, folded in a peculiar manner, and a small embryo near the base. Dried seeds, after removal of the silvery skin, provide the coffee beans of commerce. The generic name is derived from the Arabic word used for the drink, which may have come from the region of Kefa in Ethiopia.

The plant is tetraploid, and over 30 mutations have been recognized. In the bisexual flowers, pollen is shed shortly after the flower opens, and the stigma is receptive immediately. Self-pollination can occur, as seed sets even when the flowers are bagged. Pollination is also by honeybees, which collect nectar and pollen from the flowers. Dispersal is mainly by birds and mammals.

Savannah soils of moderate acidity to neutral or slight alkalinity are suitable. Very sandy soils and shallow soils are unsuitable for growing coffee. Soils should be deep, slightly acidic, well-drained loams. They should be rich in nutrients especially potash and with a generous supply of organic matter.

C. arabica thrives in a moderately humid atmosphere and prefers deep friable soil on undulating land; it is unsuited to stiff clay or sandy soils and is considered tolerant of acid soils. It thrives at 1500-2000 m or higher, ideally with rainfall 1500-2000 mm.

Despite its name, C. arabica originated in Ethiopia, where it is an understorey tree in forests. It is believed to have been introduced into Arabia before the 15th century. First planted in Java in 1690, and in the early 18th century was carried to Surinam, Martinique and Jamaica. Cultivation soon spread throughout the West Indies and Central America and favourable regions of South America. Later, it reached India and Sri Lanka. From Amsterdam, it was taken to the Philippines in 1740 and Hawaii in 1825. A single tree from Edinburgh Botanic Gardens was taken to Malawi in 1878, and from there it was introduced into Uganda in 1900 under the name ‘nyasa’. Catholic missionaries took it to Tanzania and Kenya at the end of the 19th century. The French fathers imported seeds from Aden in Yemen into Kenya in 1893. Today, nearly 90% of the world’s coffee comes from this C. arabica.

Propagation is usually by seed. The viability of the seeds is comparatively short, depending upon conditions, and it is advisable to plant within 2 months of harvesting. The older the seeds, the longer they take to germinate and they lose viability. They can be planted with the parchment attached but germination is quicker when it is removed. A traditional method of planting is to put 20 seeds in holes each 3.5 x 3.5 m at the beginning of rainy season; half will be eliminated naturally. A more successful method is to raise seedlings in shaded nurseries; at 6-12 months, seedlings are planted out to the field. It has also been successfully propagated by rooting, layering, marcotting and budding. For rooting of coffee cuttings, the single leaf-bud cutting is commonly used.

The seedlings are planted on contoured fields 2-3 m apart in 3-5 m rows. Weed control is necessary throughout the entire season. Mulches and green manure are commonly used with chemical fertilizers. Typical application consists of 175 g N, 100 g P and 175 g K per bush, the latter 2 added in 2 applications and N over a longer period (4-5 applications). Other elements are added as needed. Shading improves leaf and shoot growth but reduces root growth; however, it may be useful when the plants are young. Done at a later stage, it may reduce yields, especially when the trees are fertilized. Pruning has become an important maintenance operation. High productivity is directly dependent on good pruning practices.

Many fungi attack C. arabica coffee plants, among them Colletotrichum coffeanum and Phoma spp., associated with Elgon die-back and coffee berry disease. Other diseases include Pseudomonas garcae, a bacterial disease, and stem pitting, a viral disease. Cuscuta and Loranthus spp. parasitize trees in some areas. Witches’ broom also occurs. Many nematodes have been found with C. arabica trees, including Achromadora longiseta, Aphelenchus coffeae, Aphelenchoides parietinus, Cephalobus persegnis, Criconemella curvata and Cryptonchus abnormis.

Seed storage behaviour is intermediate. Lowest safe seed mc is 8%, unfreezable mc is 24%, viability is completely lost within 24 hours at -196 deg. C with 8% mc. Results of investigations of desiccation tolerance of 17 seed lots representing 9 cultivars received from 3 continents showed that C. arabica seeds tolerated desiccation to 7-12% mc, that is, in equilibrium with about 40-55% rh, but further desiccation reduced germination in all seed lots; moreover, viability was lost rapidly at cool (5 deg. C and 0 deg. C) and subzero temperatures (-20 deg.C) and at low moisture contents. Optimum air-dry storage environments for the maintenance of seed viability reported are ambient temperature with 10% mc, 10 deg. C with 50% rh (about 10% mc), 9 deg. C with 50% rh, 5 deg. C with 35-55% rh (about 7.5-11% mc), 10 deg. C with 10-11% mc. Excised embryos tolerated desiccation to 16.4% mc; viability was reduced to 56% and 8% on desiccation to 8.4% and 7.7% mc, respectively; no loss in viability after 1 hour’s cryostorage in liquid nitrogen with excised embryos at 16.4% mc, little loss (by 14%) in viability with excised embryos at 8.4% mc, but no excised embryos at 7.7% mc survived 1 hour in liquid nitrogen. There are about 3 200 seeds/kg.

Soil improver: The pulp and parchment are used as manure and mulches. Annual litter fall from both shade and crop trees, including pruning residues, maintain soil organic matter levels and hence the cation exchange capacity; this reduces the risk of leaching losses and permits a more efficient use of any inorganic fertilizers applied. Intercropping: C. arabica is often intercropped with food crops, such as corn, beans or rice, during the 1st few years.

Food: Dried seeds (‘beans’) are roasted, ground, and brewed to make 1 of the 2 most popular beverages in the world. In its native Ethiopia, it has been used as a masticatory since ancient times. Cooked in butter, it can be used to make rich flat cakes. Coffee is widely used as flavouring in ice cream, pastries, candies, and liqueurs. In Arabia, a fermented drink from the pulp is consumed. Fodder: Pulp and parchment are occasionally fed to cattle in India. Apiculture: Honeybees collect nectar and pollen from the flowers. The honey is light with a characteristic flavour. Mixed coffee-orange honey is very highly valued. Timber: Wood is hard, dense, durable, takes a polish well, and is suitable for tables, chairs and turnery. Poison: C. arabica seeds contain caffeine, which has been described as a natural herbicide, selectively inhibiting germination of seeds of Amaranthus spinosus. Medicine: Reported to be analgesic, an aphrodisiac, anorexic, antidotal, cardiotonic, CNS-stimulant, counterirritant, diuretic, hypnotic, lactagogue and nervine. Coffee is a folk remedy for asthma, tropine poisoning, fever, flu, headache, jaundice, malaria, migraine, narcosis, nephrosis, opium poisoning, sores and vertigo. Other products: Coffelite, a type of plastic, is made from coffee beans. Coffee with iodine is used as a deodorant.