Coffea (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Coffea L.

Protologue: Sp. pl.: 172 (1753).

Family: Rubiaceae

Chromosome number: x= 11; 2n= 44 (C. arabica); 2n= 22 (all otherCoffeaspecies)

Major species and synonyms

• Coffea arabica L., Sp. pl.: 172 (1753), synonyms: C. vulgaris Moench (1794), C. angustifolia Roxb. (1814), C. sundana Miquel (1856).

• Coffea canephora Pierre ex Froehn., Notizbl. Bot. Gart. Berl. 1: 257 (1897), synonyms: C. robusta Linden (1900), C. laurentii De Wild. (1900), C. ugandae Cramer (1913).

• Coffea liberica Bull ex Hiern - see separate article.

Vernacular names

General:

• coffee (En).
• Caféier (plant), café (product) (Fr).
• Indonesia, Malaysia and Papua New Guinea: kopi
• Philippines: kapé (Tagalog), kahana (Sulu), kapi (Ifugao, Iloko, Tagalog)
• Thailand: kafae
• Vietnam: cà phê.

C. arabica :

• arabica coffee, Arabian coffee (En).
• Caféier arabica (Fr)
• Vietnam: cà phê chè.

C. canephora :

• robusta coffee (En).
• Caféier robusta (Fr)
• Vietnam: cà phê vối.

Origin and geographic distribution

Wild plants of most species of Coffea are components of the understorey of tropical forests in Africa. Whereas many forms of C. canephora can be found in the equatorial lowland forests from Guinea to Uganda, the centre of genetic diversity of C. arabica is restricted to the south-western highlands of Ethiopia.

Arabica coffee of Ethiopian origin was already cultivated in the 12th Century in Yemen. From there it was taken to India and Sri Lanka in the 16th and 17th Centuries by Arabian travellers. The first commercial coffee production outside Arabia started in Java (Indonesia) shortly after 1699, when coffee plants originating from Yemen but raised on the Malabar coast of India were introduced by the Dutch East India Company. In the course of the 18th Century coffee spread into the Caribbean and South America through mediation of the Botanic Garden of Amsterdam which distributed plant material obtained from Java in 1710.

All the coffee plants distributed to Asia and Latin America mentioned above were of C. arabica var. arabica, usually called typica (syn.: C. arabica var. typica Cramer). The coffee introduced by the French from Yemen, first to the island of La Réunion (formerly Bourbon) in 1715, then to Latin America and eventually in the 19th Century to Africa, was different, namely C. arabica var. bourbon (B. Rodr.) Choussy. It has a more compact and upright habit, is higher-yielding and generally produces better-quality coffee than typica.

By 1860 world trade in coffee involved some 250 000 t per year, mostly from Brazil, Indonesia and Sri Lanka. On account of its superior cup quality, arabica coffee would certainly have continued to be the exclusive producer of coffee, had it not been so vulnerable to diseases, particularly to coffee leaf rust (Hemileia vastatrix) when grown at lower altitudes in equatorial zones. Coffee leaf rust had virtually wiped out coffee cultivation in Asia by 1890. Whereas in Sri Lanka coffee was replaced by tea, Indonesia continued to be a major coffee producer, switching to another coffee species, C. canephora, which proved to be resistant to leaf rust epidemics.

Robusta coffee was first introduced into Java in 1900 from Congo. Selection programmes in East Java resulted in high-yielding plant material, which formed the basis for robusta coffee production not only in Asia - major producers being Indonesia, Vietnam and India - but even in tropical Africa.

In South-East Asia, the cultivation of arabica coffee is now restricted to high-altitude areas particularly in Papua New Guinea, but also in Indonesia, Vietnam, the Philippines, northern Thailand and Burma (Myanmar).

Uses

The stimulating effect of the coffee beverage is largely derived from the alkaloid caffeine, but cured beans have to be roasted and finely ground to bring out the characteristic coffee aroma. The habit of drinking coffee as a hot watery extract from roast and ground beans is still prevalent in many countries. Vacuum-sealed packets of whole roast beans or ground coffee prepared from top quality arabicas, or various blends of arabica with robusta coffee are available, especially to the European consumer. In some producer countries it is very common to roast locally available coffee in the home and to prepare the brew (called "kopi tubruk" in Indonesia) by pouring hot water over freshly roast and ground coffee. Over the last 40 years, instant coffee as soluble powder, prepared by dehydrating extracts of roast and ground coffee, has become a very important commodity. Globally about 20% of all coffees are consumed as instant coffee. Higher rates are found in the United Kingdom (80%), Japan (40%) and the United States (30%). Although arabica coffee gives a beverage of better quality, robustas are in great demand by the instant coffee industry because of the higher yields of soluble solids. About 10% of the world's exportable coffee is decaffeinated.

Roast and ground coffee is a constituent of traditional medicines in South-East Asia, e.g. to alleviate stomachache and diarrhoea, to increase blood pressure, and as a diuretic and antidote. It is extensively used to flavour candies. In Java, it is often used to mask the odour of a corpse before funeral. Coffee pulp and parchment are applied as manure and mulch.

Production and international trade

Total world production of coffee (raw beans or green beans) was about 5.9 million t/year from 10.6 million ha over the period 1995-1999. About 70% of this is arabica coffee, mostly from Latin America (but also eastern and central Africa, India, Indonesia and Papua New Guinea), 30% is robusta from Africa and Asia and less than 1% is obtained from C. liberica and other coffees. For at least 20 of the 60 producing countries coffee contributes more than 20% to the total value of exports. Some 75% of all coffee is exported, more than 90% of it to Europe, the United States and Japan. At least half of the world population drinks coffee, average per capita annual consumption varying from 0.1 (India) - 4.5 (Brazil) kg in coffee-producing countries to 2.8 (Japan) - 10.9 (Finland) kg in consuming countries.

The price elasticity of supply is low and prices have fluctuated from US$ 1.0-5.5 per kg green coffee, with top arabicas usually fetching 50-100% more than robusta coffees. The total value of the international trade in green coffee was estimated at US$ 13.5 billion in 1997 against US$ 9.5 billion in 1996.

Coffee production in Indonesia increased from 180 000 t in 1971 to 480 000 t in 1996, mostly robusta coffee except for some 40 000 t arabica mainly from Aceh, North Sumatra, East Java, South Sulawesi, Bali and eastern Timor. C. liberica (liberica and excelsa coffees) are also grown on a limited scale, producing some 4000 t annually. Indonesia has become the third largest coffee producer after Brazil (1.5 million t arabica and 0.3 million t robusta) and Colombia (750 000 t arabica). Vietnam has shown a remarkable recovery and further expansion of its coffee production from a mere 3000 t in 1986 to 400 000 t in 1998 (95% robusta). It is now the second largest robusta-producing country, after Indonesia but before Brazil, Uganda and Ivory Coast. Papua New Guinea, with 60 000 t, is the largest arabica coffee producer in South-East Asia. The Philippines produce some 55 000 t (25% liberica and 5% arabica), Thailand 75 000 t (99% robusta), Malaysia 8000 t (50% robusta and 50% liberica coffee), all for local consumption. Altogether South-East Asia currently produces about 20% of the world coffee and 51% of all robustas.

In most countries coffee is a smallholder crop. For instance, in Indonesia there are about 60 000 ha of government and private coffee estates (size 30-1500 ha), while the remaining 1 100 000 ha of coffee are smallholder farms of 0.3-2.0 ha. Smallholdings also dominate in Malaysia (90%), Thailand (90%), Papua New Guinea (70%) and the Philippines (60%). In Vietnam coffee used to be mostly produced by government-controlled plantations or collective farm units, but as much as 50% of the coffee is now produced by smallholders.

Four main classes of coffee are distinguished in the international coffee trade. They are, in descending order of quality:

• Colombian milds, indicating washed arabicas from Colombia, Kenya and Tanzania;

• other milds that are also washed arabicas;

• dry-processed or hard arabicas (e.g. Brazil, Ethiopia);

• robustas, washed or dry-processed.

Properties

The coffee bean consists largely of endosperm with the following approximate composition per 100 g dried beans: water 10-13 g, proteins and free amino acids 11-16 g, lipids 12-14 g, sucrose and reducing sugars 5-9 g, cellulose and other polysaccharides 32-48 g, chlorogenic and other acids 10-15 g, ash and minerals 4 g. The caffeine content in arabicas ranges from 0.6-1.7% and in robusta coffee from 1.5-3.3%. During roasting most of the water evaporates, the sugars caramelize, the polysaccharides carbonize and many compounds are converted into volatiles (so far about 700 have been identified).

Coffee quality is determined by experienced tasters: visual assessment of the raw bean is followed by trial roasting, brewing and organoleptic evaluation of the beverage. The liquor of high-quality washed arabicas (raw beans typically have a bluish-green colour) will be richly aromatic (flavour) with a pleasing acidity; dry-processed arabicas will be less acid but with more body. Raw beans of washed or dry-processed robustas are brownish in colour and the liquor will have a neutral flavour at best, little acidity, considerable body but a somewhat harsh, bitter and astringent taste.

The 1000-seed weight (18% moisture and with parchment) is 450-500 g for arabica and about 400 g for robusta coffee.

Description

• Shrubs or trees.
• Leaves opposite, usually with characteristic, connate, interpetiolar, subtriangular stipules.
• Inflorescence consisting of axillary clusters of cymes in both axils of a leaf pair or terminal.
• Flowers bisexual, often white; calyx tubular with 4-5(-8) small teeth or lobes; corolla tubular, 4-8-lobed; stamens inserted in throat or lower, exserted or enclosed; ovary inferior, 2-celled, with 1 ovule per cell; style filiform, stigma with 2 linear branches.
• Fruit a drupe (in coffee often called "berry"), with red to black exocarp, usually fleshy mesocarp and horny endocarp containing 2 stones usually.
• Seed (in coffee often called "bean") plano-convex, on the flat side usually grooved.

C. arabica.

• Evergreen, glabrous shrub or small tree, often multi-stemmed, 4-5 m tall, in cultivation pruned to 1.8-2.5 m. Taproot often less than 1 m long, but some lateral roots may grow downwards to depths of 3-4 m for firm anchorage; 90% of feeding roots in the top 30 cm of the soil.
• Leaves decussate; petiole up to 2 cm long; blade ovate, (5-)10-15(-25) cm × 5-10 cm, acute at base, margin somewhat undulate, apex acuminate, glossy, dark green above, lighter green beneath, with domatia (small cavities) beneath at insertion of lateral veins, giving slight protuberances above.
• Flowers in axillary clusters, 10-30 per node, hermaphrodite, fragrant, creamy white, with short pedicel; calyx small and 5-denticulate; corolla tube 10 mm long, lobes 5, ovate, 8 mm long, white; stamens 5, inserted on corolla tube between lobes, anthers bilocular, opening lengthwise; pistil with bilocular ovary, style 12-15 mm long.
• Fruit ovoid-ellipsoidal, 12-18 mm × 8-15 mm, initially green but turning red at maturity, mesocarp fleshy, endocarp (parchment) fibrous, surrounding seeds.
• Seed ellipsoidal, 8-12 mm long, 2 per fruit; testa thin (silver skin), endosperm abundant, embryo at base of the seed, small.
• Seedling with epigeal germination.

C. canephora differs from C. arabica in the following characteristics:

• Larger tree, up to 8-12 m tall, with long flexible branches, shorter taproot and shallower rooted.
• Leaves 15-30(-40) cm × 5-15 cm with corrugated surface and petiole 1-2 cm long.
• Flowers white, up to 80 flowers per node, with 5-7-lobed corolla; stamens and style well exserted.
• Fruits smaller, 8-16 mm long.
• Generally C. canephora is a more vigorous grower than C. arabica and shows a much higher polymorphism.

Growth and development

Coffee has no seed dormancy. At ambient temperatures seed viability is lost within 3-6 months, but when stored moist at 15°C it can be maintained at 90% for 15 (robusta) to 30 (arabica) months. Longer storage by cryopreservation may soon prove possible. After sowing in wet sand, germination is complete within 6-8 weeks. Removal of the parchment halves the germination time. The cotyledons unfold and the first pair of leaves appears 10-12

weeks after sowing. Subsequent leaf pairs, always at right angles to the pair below, are formed at 3-4-week intervals. The first pair of side shoots emerges at the node of the 5-9th leaf pair. Seedlings 30-40 cm tall are ready for field planting 7-9 months after sowing for robusta and 11-15 months for arabica.

Coffee develops according to the architectural model of Roux, which is characterized by a continuously growing monopodial orthotropic stem with plagiotropic opposite branches. A series of buds is found in the axil of each leaf on the orthotropic seedling stem. The highest bud ("head of series") produces a plagiotropic side shoot ("primary"), while the lower buds remain dormant; when forced, orthotropic suckers grow out. The series of buds present in the axil of each leaf of plagiotropic shoots give rise to inflorescences or plagiotropic side shoots ("secondaries"); buds on plagiotropic shoots cannot develop into orthotropic shoots.

Under ideal conditions a 3-year-old unpruned arabica tree (2 years in the field, producing its first crop) is cone-shaped with 25-30 pairs of primary branches on a main stem 150-180 cm tall. Annual shoot growth on primaries may be 22-35 cm with 10-12 new nodes. The fruit of such a tree is borne on the nodes close to the main stem of the lower 15-20 primaries. Nodes flower only once; within a few years the crop on the younger primaries high on the main stem is beyond the reach of pickers, while the crop lower in the tree dwindles as shoot vigour declines. To restrict tree height and maintain vigour in the basal parts, strict juvenation pruning is needed. Cutting back the main stem stimulates the emergence of orthotropic suckers from serial buds, especially below the cut and at the base of the stem. One or several of these basal suckers can replace the main stem, starting a new cycle of productive years.

Coffee shoots tend to grow continuously, but their growth rate is readily slowed down to a virtual standstill by adverse external (e.g. drought) or internal (e.g. a good fruit crop) factors. Growth is rapid at the beginning of a rainy season.

During rapid extension growth no flowers are initiated, but as shoot growth subsides, floral development starts on 5-7-month-old nodes and gradually proceeds towards the shoot tip. Daylength (12-18 h photoperiods) has little influence on floral initiation in coffee. Flower buds become dormant before they are fully developed and as the season progresses more flower buds enter dormancy. Flower bud dormancy is progressively decreased by continued water stress; rapid rehydration - usually accomplished by the first showers at the onset of the rainy season - induces blossoming 6-12 days later. Young buds that are still dormant are triggered by subsequent showers. The more or less simultaneous release from dormancy synchronizes flowering and fruit growth.

C. arabica is self-fertile - less than 10% of the flowers are naturally cross-pollinated - and fruit set is high. The fruitlets hardly grow during the first 6-8 weeks ("pinhead" stage). Since flowering follows the early rains this means that fruit growth is delayed until the rainy season has set in and shoot growth has resumed. In bimodal rainfall areas flowering occurs at the beginning of both rainy seasons and the associated fruit growth periods overlap. The fruits are mature in 8-9 months.

Coffee fruits are strong assimilate-accepting sinks and the tree is unable to regulate the crop load effectively by shedding fruitlets. The key issue in coffee growing is therefore the prevention of excessive cropping that leads to biennial bearing or even shoot dieback. The use of shade trees has a tempering effect on shoot growth, improves leaf retention, but also reduces flower initiation. Without shade, fruiting is much heavier, with up to 20 fruits per node. At least 20 cm² leaf area (one leaf = 30-40 cm²) is needed to support each fruit without affecting vegetative growth. Crop husbandry is therefore aimed at maintaining enough foliage to sustain the crop, as well as new shoot growth throughout the season by pruning, mulching, irrigation, fertilizing, control of diseases and pests and "tonic" sprays of fungicide. The latter treatment improves leaf retention by 2-3 months, particularly in climates with distinct periods of water stress, resulting in progressive yield increases of 50-100%.

The growth of robusta is comparable with arabica, except that primaries become longer and produce few secondary branches. Flower initiation follows shoot growth more closely and flowering periodicity becomes less distinct, especially when rainfall is well-distributed over the year. Nodes on robusta branches may flower twice: first in the season in which the shoot is formed and again two years later. In the intervening year the fruits at these nodes should prevent repeated flowering. C. canephora is allogamous, with a gametophytic system of self-incompatibility. Robusta fruits take 9-11 months to mature.

Other botanical information

Coffea belongs to the subfamily Ixoroideae and the tribe Coffeae. Recent taxonomic studies, including the application of molecular marker technologies to chloroplast and nuclear DNA extracted from several species, confirm a monophyletic origin of all species of the genus Coffea . The process of differentiation into clusters of related species coinciding with geographic regions in Africa has not yet progressed into strong genetic barriers and, therefore, does not justify the distinction into sections as applied in earlier taxonomic classifications. Altogether about 100 species (taxa) of the genus Coffea have been identified so far. They are without exception indigenous to the forests of tropical Africa and Madagascar and all are diploid species, except the allotetraploid C. arabica, which has its origin in the highland forests of south-western Ethiopia. Species close to C. eugenioides S. Moore and to C. canephora (or C. congensis Froehner) are the most likely maternal and paternal progenitors respectively of C. arabica.

There are numerous cultivars of the typica and bourbon varieties of arabica coffee (preferably classified as cultivar groups), but all originate from the genetically very narrow base population of Yemen: "Typica National", "Bourbon", "Mundo Novo", "Caturra", "Blue Mountain", "Maragogipe", "SL 28", "N 39", "Kent", "Padang" and "Blawan Pasumah". Some cultivars are selections from spontaneous interspecific hybrids, e.g. S (288, 333, 795) and BA selections from "India" and "Hibrido de Timor", or from germplasm collections in Ethiopia and nearby Sudan such as "Geisha", "Abyssinia" and "Rume Sudan". "Catimor", from a cross between "Caturra" and "Hibrido de Timor", is a compact cultivar resistant to most races of coffee leaf rust. "Icatu", developed in Brazil from an interspecific cross between C. arabica and (tetraploid) C. canephora followed by backcrossing to C. arabica and selection, is also highly resistant to coffee leaf rust.

In the polymorphic C. canephora two subpopulations (cv. groups) are distinguished:

• "Congolese", with erect growth habit and large leaves, of Central African origin, including robusta forms; and

• "Guinean", with a more spreading growth habit and smaller leaves and fruits, of West (Guinean coast) and Central African (Uganda) origin, including "nganda" and "kouilu" forms.

Important robusta cultivars (clones or seedlings) are the BP and SA selections of Java, "S274" and the BR series of India, the INEAC selections of Congo, and the IRCC selections of Ivory Coast.

Interspecific hybrids such as "Congusta" of Java and the C×R cultivar of India (between C. congensis and C. canephora) and "Arabusta" (between C. arabica and tetraploid C. canephora) also have potential for robusta coffee production at medium to low altitudes.

Ecology

Arabica coffee requires an average daily temperature of 18-22°C with a maximum not exceeding 30°C. This restricts its cultivation to high altitudes in equatorial (0-7N/S) areas (1000-2100 m) or lower altitudes (300-1100 m) further from the equator, as in India, Vietnam, Thailand, and South America (9-23N & S). Temperatures near 0°C will kill the leaves immediately, while long periods of hot (and dry) weather will cause wilting, even at high soil moisture. In the humid lowland tropics, arabica coffee will show poor flowering (star flowers) and shoot dieback. Annual rainfall requirements are 1400-2200 mm with no more than 3 months of less than 70 mm. Lower rainfall can be compensated for by irrigation (e.g. East Africa).

Robusta coffee is well adapted to the warm and humid equatorial climates with average temperatures of 22-26°C, minimum not below 10°C at altitudes of 100-800 m, and well-distributed annual rainfall of 2000 mm or more.

Coffee is able to grow on a wide range of soils provided these are deep (at least 2 m), free-draining loams with a good water-holding capacity, fertile and slightly acid (pH 5-6). The topsoil should contain at least 2% organic matter. The parent material of the major coffee soils may be lava and tuff (e.g. Kenya), volcanic ash (Indonesia, Central America), or basalt and granite (Brazil, West Africa, India). An exception is the western highlands of Papua New Guinea, where high rainfall well distributed over the year permits successful coffee production on clay soil of just 20-30 cm deep over compacted clay of volcanic origin.

Propagation and planting

Most cultivars of the self-pollinating arabica coffee are practically pure lines, propagated by seed. In Kenya F₁hybrid seeds are produced by hand pollinating new disease-resistant arabica cultivars. Robusta coffee is cross-pollinating and is often propagated from seed obtained from biclonal or polyclonal gardens. Vegetative propagation of high-yielding robusta clones is applied on a limited scale in Java (grafting and rooted cuttings), in Congo, Ivory Coast and Uganda (rooted cuttings). New methods of in vitro multiplication in arabica (hybrid cultivars) and robusta coffee, including micro-propagation and somatic embryogenesis, are gradually being applied as well. Seedlings or plants from rooted cuttings are raised on beds or in polythene bags in shaded nurseries. In South-East and South Asia, coffee is grown either in pure stands with temporary or permanent shade trees, or in association with perennial crops (coconut palms, rubber, clove, fruit trees and pepper), or in home gardens with food crops, bananas and perennial crops. In East Africa and South America, arabica coffee is usually grown without shade.

Young plants of 7-15 months old are planted in the field in large holes (60 cm × 60 cm × 60 cm) refilled with topsoil, organic material and rock phosphate. Various spacings and rows (right lines and squares) are used in densities of 1300-2800 trees/ha for arabica and 1100-1400 trees/ha for robusta coffee. High density planting of 3300-5000 trees/ha, as applied in Latin America and East Africa with compact arabica cultivars like "Caturra", "Catimor", and the F₁hybrid "Ruiru 11", is also common in Indonesia and in Papua New Guinea. On slopes of more than 30it is necessary to plant along contour lines or on terraces to prevent erosion.

Common shade trees are Leucaena leucocephala (Lamk) de Wit, Erythrina subumbrans (Hassk.) Merrill, Gliricidia sepium (Jacq.) Kunth ex Walp., Paraserianthes falcataria (L.) Nielsen and Grevillea robusta A. Cunn. ex R. Br. If cultivation is intensive and inputs are optimal, higher yields are obtained with unshaded coffee but at lower standards of crop management or sub-optimal ecological conditions shade will prevent overbearing and shoot dieback.

Husbandry

Pruning is essential in coffee production: (a) to achieve a tree of the desired shape, (b) to maximize the amount of new wood for the next season's crop, (c) to maintain a correct balance between leaf area and crop, (d) to prevent overbearing and thus reduce biennial production, and (e) to facilitate disease and pest control. The main pruning systems are:

• single-stem capped at 1.5-1.8 m (Indonesia, Malaysia) eventually resulting in an umbrella-shaped tree;

• multiple-stem on 2-5 orthotropic capped or uncapped stems (Papua New Guinea, Vietnam, Thailand);

• agobiado, which is a multiple-stem system on a main stem that has been bent over at an early age (Philippines);

• rejuvenation when trees are old and yields are low, by stumping to 30 cm above the ground to encourage new orthotropic shoots.

It is very important to suppress noxious weeds, particularly couch grass (Digitaria scalarum (Schweinf.) Chiov.), by careful tillage without damaging the superficial feeder roots, herbicides, mulching and/or leguminous cover crops.

Fertilizer requirements depend on crop yield and nutrient status of the soil. Nutrients removed by harvesting 6 t of fruits of robusta coffee, equivalent to 1 t of green beans, are: 35 kg N, 6 kg P₂O₅, 50 kg K₂O, 4 kg CaO, 4 kg MgO, 0.3 kg Fe₂O₃and 0.02 kg Mn₃O₄. Fertilizer applications should be based on the nutrient status of the tree, which can be accurately determined by foliar analysis. Generally, nitrogen fertilizers at rates of 50-100 kg N per ha per year give clear yield responses. Responses to potassium fertilizer vary from zero in mulched coffee grown on volcanic soils rich in potassium (e.g. East Africa) to highly significant on soils with a low K status: 0-400 kg K₂O per ha per year. Very high K application may induce Mg deficiency. Phosphate is often applied as compound fertilizers (2-1-2), but its effect is greatest in foliar applications. Calcium in the form of lime is used to correct soil acidity. Magnesium deficiency is best corrected by foliar applications, as are minor elements such as boron and manganese. Organic manures - stable manure, cover crops, mulch and decaying coffee pulp - are not only alternatives to chemical fertilizers, and often the only fertilizers available to smallholders, but are also essential to maintain the humus content of the soil and to improve the soil texture.

Diseases and pests

Coffee leaf rust (Hemileia vastatrix) is the major disease in arabica coffee and is present in all coffee-producing countries, including South-East Asia. It reached Papua New Guinea in 1986. Control by spraying is more effective using copper-based than using systemic fungicides. A new development is the application of granular systemic fungicides to the soil. The very destructive coffee berry disease caused by Colletotrichum kahawae (syn. C. coffeanum) of arabica coffee is still restricted to Africa, although climatic conditions in certain high-altitude areas of Latin America and Asia are thought to be favourable to epidemic outbreaks. Robusta coffee is usually resistant to both diseases. Diseases of both coffee species include brown eye spot (Cercospora coffeicola) on leaves of young coffee, tip dieback caused by Rhizoctonia spp., vascular wilt disease or tracheomycosis caused by Fusarium xylarioides (perfect stage: Gibberella xylarioides), root diseases caused by Fusarium solani, Armellaria mellea, Fomes noxius, Rosellinia spp. and Rigidoporus lignosus, particularly on recently cleared land or where shade trees have been removed, and damping-off in coffee nurseries caused by Rhizoctonia solani.

Several important nematodes attack both arabica and robusta coffee: Meloidogyne spp. causing root knots and galls, Pratylenchus coffea, Radopholus similis and Rotylenchus spp.

Over 900 insect species are known to infest coffee. Major pests on coffee in South-East Asia are, in order of importance: coffee berry-borer (Stephanoderes hampei) particularly in robusta coffee, various stem-borers (Xyleborus spp., Xylotrechus quadripes, Zeuzera coffeae), shot-hole borer (Xylosandrus compactus), green scale (Coccus viridis), brown scale (Saissetia coffea) and mealy bug (Planococcus citri). Integrated pest management (IPM) in coffee, based on early warning systems in combination with chemical, cultural and biological (parasitoids, predators, pathogens and sex-pheromone traps) control, is more effective than frequent application of broad-spectrum and persistent insecticides. Maintenance of the right microclimate is also essential for effective IPM in coffee.

Harvesting

Selective picking of ripe fruits of coffee at 7-10 day intervals is common in Java, Sumatra, Sulawesi and Papua New Guinea, where harvesting extends over a period of 7-9 months. Where the harvesting season is shorter or the cost of hired labour higher, as in South Sumatra and in most other regions in South-East Asia, whole branches are stripped when the majority of fruits are ripe. Costs of harvesting are 2-3 times higher for selective picking than strip picking: 8-9 kg coffee/man-day are hand-picked in Aceh (North Sumatra), whereas 20 kg/man-day are obtained in Lampung (South Sumatra) by stripping. In Java, coffee beans are sometimes collected from marten ("luak") droppings and marketed as "kopi luak". This coffee is regarded as being of high quality because it is certain to have been derived from ripe coffee fruits.

Yield

Yield may vary from 200 kg green coffee beans per ha from low-input smallholder plots to 2 t/ha for arabica and 3.5 t/ha for robusta coffee at conventional spacings and without shading. Yields of 5 t/ha have been obtained in high-density experimental plots of arabica coffee in Colombia and Kenya. Average yields/ha of robusta coffee per region in Indonesia are: East Java 600 kg (mostly estates), Central Java 350 kg, Lampung 750 kg and Aceh 600 kg. For arabica coffee, average yields per ha vary from 800 kg in East Java to 950-1000 kg in Aceh and South Sulawesi. The national average in Vietnam and in Papua New Guinea is about 1.3 t/ha.

Handling after harvest

There are two methods of post-harvest handling in coffee.

• The wet process: ripe fruits are pulped within 12-24 hours after harvesting, fermented to degrade the mucilage, washed, carefully dried in the sun (7-10 days) or mechanically (6-20 hours) or by a combination of both methods, and stored as dry (11-12% moisture content) parchment coffee. This process is carried out in coffee factories owned by estates and smallholder cooperative societies, or with small hand-pulpers and basins by individual smallholders.

• The dry process: fruits from strip picking - various stages of green, ripe and overmature fruits - are dried directly for 3-4 weeks in the sun on platforms or mechanically (2-3 days). Dry-processed coffee is more difficult to store than parchment coffee because of its strong hygroscopic properties.

Curing of dried parchment coffee - including hulling to remove the parchment, polishing to remove remains of silver skin and grading - takes place in central coffee mills. Dry-processed coffee is treated in a similar manner, but requires a different type of huller. The clean coffee is graded according to international standards of size and shape of beans, colour and percentage defects (broken beans, stones, husks). The clean green coffee is exported in bags of 60-70 kg, and can be stored under dry and cool conditions for 1-2 years without loss of quality. The final stage of coffee processing - blending, roasting and packaging as whole beans or ground coffee - always takes place close to the consumer market, to assure optimum quality. About 20% of the green coffee is processed into instant coffee.

Genetic resources

Systematic collections of wild and semi-cultivated C. arabica in the primary centre of genetic diversity in Ethiopia were made by the FAO coffee mission in 1964/65, by a coffee mission of the "Institut de recherche pour le développement" (IRD, formerly ORSTOM) in 1967 and by the Ethiopian Institute of Agricultural Research since 1970. This valuable material is preserved and being studied at coffee research institutes in Ethiopia, Kenya, Tanzania, Ivory Coast, Cameroon, Madagascar, Costa Rica, Brazil, Colombia, India and Indonesia. IRD has made several collections of germplasm of C. canephora and other diploid species in primary centres of genetic diversity in West and Central Africa since 1975 and in Madagascar since 1960. This material is now available at research institutes in Ivory Coast, Cameroon, the Central African Republic and Madagascar. The Indonesian Coffee and Cocoa Research Institute (ICCRI) maintains germplasm collections for C. arabica, C. canephora and other Coffea species at 3 locations in Java (2000 accessions). Absence of strong genetic barriers between species of the genus Coffea offers considerable prospects of introgressing desirable characters from wild into the two most important cultivated species by interspecific hybridization.

The International Plant Genetic Resources Institute (IPGRI) emphasizes the great urgency for intensifying germplasm collection within the still existing wild populations of Coffea species, in tropical Africa and Madagascar, before the natural habitats disappear.

Breeding

Arabica coffee represents a rare example of a woody perennial to which breeding methods common to self-pollinated crops have been applied successfully. Most of the cultivars currently grown in the world are pure lines developed by selection within genetically narrow source populations.

Breeding for resistance to coffee leaf rust started in India in the 1920s but was later also taken up in Angola, Brazil and Colombia. Much of the fundamental work on Hemileia vastatrix - identification of physiological races of the pathogen and the genetics of resistance in the host - was performed and coordinated by the Coffee Rust Research Centre at Oeiras in Portugal. One result was the new cultivar Catimor, certain lines of which are homozygous for dominant resistance genes SH₆-SH₉, making this cultivar resistant to all known races of coffee leaf rust. The grave threats posed by coffee berry disease (Colletotrichum kahawae) to arabica coffee in Africa prompted an entirely new breeding programme in Kenya in 1971, resulting in F₁hybrid cultivars resistant to both diseases in 1986. Selection for resistance to coffee berry disease is also being carried out in natural coffee populations in Ethiopia. The demand for resistance to both diseases to be combined with high yield and bean quality, as well as with compact growth for high-density planting, led to fundamental studies being carried out in Kenya on the inheritance of resistance to coffee berry disease and of yield and quality components.

Robusta coffee is a strictly cross-pollinating species; inbreeding is prevented by self-incompatibility. All plants in a seedling population will be highly heterozygous, and desired genotypes can only be fixed by vegetative propagation. Plots of cross-compatible robusta clones may outyield fields established from seedlings by 40-50%. However, in response to poor farmer take-up and major logistic problems connected with conventional methods of vegetative propagation, coffee breeders in Indonesia, Congo, Ivory Coast and Vietnam eventually adopted breeding plans based on recurrent selection, leading to polycross seed from clonal gardens.

Large-scale in vitro propagation by embryogenesis has been proven feasible and could overcome these problems. The possibility of developing pure inbred lines through haploidy, as a basis for F₁hybrid seed cultivars, is currently being studied in Ivory Coast. Such a breeding plan also includes interpopulation hybrids with a high yield potential.

Earlier expectations that arabica × robusta interspecific crosses, such as the Arabusta hybrids developed in Ivory Coast, would increase quality in traditional robusta production in the tropical lowlands of Africa and Asia have not materialized so far.

Prospects

The exploitation of genetic resources in Coffea did not start until recently, and therefore there are high hopes for further improvement in yield, disease and pest resistance and other desirable characteristics, by conventional and innovative breeding methods. Molecular markers are increasingly being applied in coffee for the detection of genetic diversity and in marker-assisted selection. In the long term genetic transformation could contribute to host resistance to important pests (e.g. berry borer). In South-East Asia, ecological conditions are favourable for coffee and production per ha could be increased considerably by more intensive crop management.

On the other hand, the high probability of continuous overproduction of coffee at mondial level and the pressure to shift land use on fertile land to food crop production to feed the ever-increasing population would make further expansion of coffee production a questionable policy. However, the spectacular yields obtained in close-spaced and intensively managed coffee become a realistic proposition with new compact-growing and disease-resistant cultivars. This would mean that national coffee quotas could in future be met from less than half of the land currently under coffee. Land would thus become available for food cropping and possibly other land-use systems.

Literature

• Charrier, A. & Eskes, A.B., 1997. Les caféiers [Coffees]. In: Charrier, A., Jacquot, M., Hamon, S. & Nicolas, D. (Editors): L'amélioration des plantes tropicales [Tropical plant breeding]. Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD) & Institut français de recherche scientifique pour le développement en coopération (ORSTOM), Montpellier, France. pp. 171-196.
• Clarke, R.J. & Macrae, R. (Editors), 1985-1988. Coffee. Vol. 1. Chemistry, Vol. 2. Technology, Vol. 3. Physiology, Vol. 4. Agronomy, Vol. 5. Related beverages, Vol. 6. Commercial and technico-legal aspects. Elsevier Applied Science, London, United Kingdom. Vol. 1 (1985) 306 pp., Vol. 2 (1987) 321 pp., Vol. 3 (1988) 388 pp., Vol. 4 (1987) 334 pp., Vol. 5 (1987) 214 pp., Vol. 6 (1988) 233 pp.
• Clifford, M.N. & Willson, K.C. (Editors), 1985. Coffee: botany, biochemistry and production of beans and beverage. Croom Helm, London, United Kingdom. 457 pp.
• Cramer, P.J.S., 1957. A review of literature of coffee research in Indonesia. Miscellaneous Publication No 15. Inter-American Institute of Agricultural Sciences, Turrialba, Costa Rica. 262 pp.
• de Graaff, J., 1986. The economics of coffee. Economics of crops in developing countries No 1. Pudoc, Wageningen, the Netherlands. 294 pp.
• Eskes, A.B., 1983. Incomplete resistance to coffee leaf rust (Hemileia vastatrix). Doctoral Thesis Wageningen Agricultural University, Wageningen, the Netherlands. 140 pp.
• Krug, C.A. & de Poerck, R.A., 1968. World coffee survey. FAO Agricultural Studies No 76. Food and Agriculture Organization of the United Nations, Rome, Italy. 476 pp.
• Rodrigues Jr, C.J., Bettencourt, A.J. & Rijo, L., 1975. Races of the pathogen and resistance to coffee rust. Annual Review of Phytopathology 13: 49-70.
• van der Vossen, H.A.M., 1982. Consequences of phytotonic effects of fungicide to breeding for disease resistance, yield and quality in Coffea arabica. Journal of Horticultural Science 57: 321-329.
• van der Vossen, H.A.M., 1998. Quality aspects in arabica coffee breeding programmes in Africa. In: 17ème Colloque Scientifique International sur le Café, 20-25 July 1997, Nairobi, Kenya [17th International Scientific Colloquium on Coffee, 20-25 July 1997, Nairobi, Kenya]. ASIC (Association Scientifique Internationale du Café), Paris, France. pp. 430-438.
• Walyaro, D.J., 1983. Considerations in breeding for improved yield and quality in arabica coffee (Coffea arabica L.). Doctoral Thesis Wageningen Agricultural University, Wageningen, the Netherlands. 119 pp.
• Wrigley, G., 1988. Coffee. Tropical Agriculture Series. Longman Scientific & Technical, Harlow, United Kingdom. 639 pp.

Authors

H.A.M. van der Vossen, Soenaryo & S. Mawardi