Breeding coffee (coffea arabica) for sustainable production

Abstract

Coffee is one of the worlds most valuable export commodities, ranking second in the world market after petroleum products. The total retail sales value exceeded US$70 billion in 2003 and about 125 million people depend on coffee for their livelihoods in Latin America, Africa and Asia (Osorio 2002). Commercial production relies on two species, Coffea arabica L. and C. canephora Pierre. The cup quality (low caffeine content and fine aroma) of C. arabica makes it by far the most important species, representing 70% of the world production. C. arabica has its primary centre of genetic diversity in the highlands of southwest Ethiopia and the Boma Plateau of Sudan. Wild populations of C. arabica have been also reported in Mount Imatong (Sudan) and Mount Marsabit (Kenya) (Thomas 1942, Anthony et al. 1987). Cultivation of C. arabica started in southwestern Ethiopia about 1,500 years ago (Wellman 1961). Modern coffee cultivars are derived from two base populations known as Typica and Bourbon which were spread worldwide in the eighteenth century (Krug et al. 1939). Historical data indicate that these populations were composed of progenies of very few plants, that is, only one for the Typica population (Chevalier and Dagron 1928) and the few plants that were introduced to the Bourbon Island (now Reunion) in 1715 and 1718 for the Bourbon population (Haarer 1956). Breeders exploited these narrow genetic bases, resulting in Typica- and Bourbon-derived cultivars with homogeneous agronomic behaviour characterised by high susceptibility to many pests and low adaptability (Bertrand et al. 1999). As with cereal crops, Arabica coffee growing was turned completely upside down by a veritable green revolution over the 19701990 period. However, as it was not a matter of solving the worlds hunger problems, which was the case for rice, wheat or maize (Borlaug 1968), the Arabica revolution received little media attention. Traditionally, coffee was grown under forest trees or planted trees (often used for firewood). Use of traditional varieties (Bourbon, Typica) with a tall growth habit, or even wild types (Ethiopia), with planting densities of around 1,5003,500 trees/ha was commonplace. Fertiliser use in such a system was very limited (0100 units of nitrogen). Through several concurrent technical advances in 1950s and 1960s that cropping system evolved and the conditions for a veritable green revolution were created. From an extensive system under forest cover, a switch was made to full sunlight with abundant use of fertilisers (notably 300600 units of nitrogen/ha and 150800 units of potassium) and pesticides. As a result, yields more than doubled from 150 to 500 kg of green coffee/ha to more than 1,000 kg, and even exceptional yields of more than 3,500 kg/ha under good ecological conditions. Just as the new varieties of wheat were at the heart of the green revolution, the new semi-dwarf mutant varieties (that is Caturra and Catuai derived from the traditional Bourbon and Typica varieties; Carvalho 1988) served as a catalyst (Castillo 1990) in this coffee-growing revolution. By using those varieties, it was possible to double or even treble planting densities (5,0008,000 trees/ha). The plantation sector moves into the new millennium and the coffee industry has several new challenges to address. The coffee production is surplus worldwide and the prices are highly variable and frequently low. Hence, minimising the production cost and maintenance of product quality to suit consumer preferences are the key factors to thrive in highly competitive international market. The new wave of sustainable development and the reality of World Trade Organization (WTO) have led to new quality trends in commodity sector. Accordingly, stringent environmental/eco-friendly quality parameters are being imposed in producing countries. These developments have direct impact on R&D and there is a need to reorient the research priorities to address the new challenges. Genetic improvement for sustainable production appears therefore as an essential issue. In this chapter, we review research aspects linked to the origin and genetic diversity of C. Arabica, the introgressive breeding, the development and micropropagation of improved F1 hybrid varieties.