Breeding strategies and cultivated varieties
Arabica Varieties
About 60% of the coffee produced worldwide (84.3 million 60 kg bags in 2014/2015, according to ICO statistics) comes from Arabica beans. Traditional varieties like Typica and Bourbon, originally from Yemen, along with their variations like Caturra, have long been known for high productivity and consistent quality. Some selections such as Laurina, Moka, or Blue Mountain are prized for their premium quality. However, coffees from regions like Ethiopia and Sudan, such as Gesha and Rume Sudan, are considered wild or semi-wild, catering to niche markets due to their lower productivity.
In the early 1980s, the threat of coffee leaf rust (CLR) disease pushed geneticists to develop resistant Arabica varieties. Although Arabica and Robusta species are genetically similar, creating hybrids proved to be a lengthy process for introducing resistance genes. Thus, breeders primarily turned to the Timor hybrid (a natural blend of Arabica and Robusta) as a source of resistance genes. This effort resulted in varieties like Catimors and Sarchimors, which offer both productivity and rust resistance. However, some new varieties like Costa Rica 95 have faced criticism for their inferior quality compared to traditional ones. Yet, selective breeding has shown that focusing on quality can lead to introgressed Arabica varieties with excellent cup quality.
In Colombia, varieties like Colombia and Castillo have been evaluated for their sensory attributes. Studies have shown that while these varieties are composite, their sensory profiles are comparable to traditional varieties like Caturra, Typica, or Bourbon. Similarly, Ruiru 11, a composite cultivar from Kenya, offers disease resistance, high yield, and fine quality.
In Brazil, extensive selection efforts since 1973 have resulted in various lineages from germplasms like Catuaí, Mundo Novo, and Sarchimor. While some show superior quality, others have issues like a high proportion of shell beans and poor beverage quality.
Robusta Varieties
Robusta breeding faces challenges due to the species self-incompatibility. Breeding strategies involve selecting clones or hybrids propagated through controlled pollination. Massal selection, mainly practiced in Brazil and Vietnam, and hybridization between distant genetic groups, developed in Ivory Coast, are the primary approaches.
Robusta cultivation began in the 19th century to address damages caused by CLR on Arabica plantations. Robusta landraces from regions like the Belgian Congo were favored for their vigor, productivity, and CLR resistance. Over time, clonal selections in countries like Uganda, Congo, and Ivory Coast have improved productivity and bean size.
Genetic basis of coffee quality
Biochemical Determinants of Quality
Coffee quality encompasses physical, chemical, and sensory attributes influenced by various factors, including genetics, physiology, and agricultural practices. Genetic potential plays a crucial role in determining quality, affecting size and biochemical composition.
Different Coffea species exhibit variations in biochemical compounds linked to quality attributes. Understanding these variations is crucial for coffee breeders to enhance commercial varieties.
Genetics of Quality
Studies have shown that quality traits in both Arabica and Robusta coffees are heritable. Hybrids from parents with good quality attributes tend to produce coffee with superior quality. Genetic mechanisms influencing traits like caffeine content and bean weight have been identified, offering avenues for improvement through conventional breeding.
Experimental Approaches
New analytical methods and DNA technologies have improved the study of sensory quality in coffee. Metabolomics and transcriptomics offer insights into biochemical and molecular markers associated with quality traits, aiding modern breeding strategies.
The future in coffee breeding
Climate change poses challenges for coffee production, emphasizing the need for varieties adapted to higher temperatures. Future breeding efforts will focus on combining high sensory quality with resilience to biotic and abiotic stresses.
For Arabica, hybrid varieties show promise for increased productivity and adaptability. Robusta breeding can leverage untapped genetic diversity to develop hybrids with improved yield and vigor. Despite progress in identifying genetic markers for quality, challenges remain in implementing them efficiently in breeding programs. The recent decoding of the C. canephora genome offers promising tools for future research and breeding endeavors.