None of the traditional cultivars of arabica coffee are completely resistant to all the pathogens we listed in Chapter 4 of this course, but their flavour potential is so good that the specialty market still encourages farmers to plant them. The key to safe and secure performance of a traditional cultivar is to grow it in an environment that resembles the climate that has existed in the cloud forests of Ethiopia since coffee cultivation began. Colombian agronomist Leonardo Henao explained to us that he no longer advises farmers to grow traditional varieties if their climate doesn’t fall into the 17–21°C (64–70° F) temperature range.
In a review of the existing literature, J. Sha et al. (2014) found shade was effective in reducing temperature in 100% of the studies. However, this approach has its limits. Under 45% shade protection — the level considered optimal for increasing plant yields — the temperature of outer leaves of trees was reduced by only 2° C, compared with the temperature of neighbouring trees that experienced full sun exposure (P Vaast et al., 2015).
Owing to recent advances in sensory science, breeding organisations such as World Coffee Research have become more aware of the flavour potential of important varieties of arabica, such as geisha. Species such as Coffea liberica can comfortably endure temperatures up to 40° C, and they carry some of the genes from geisha that are responsible for its incredible floral aromas (A Davis, 2013). At the moment it is not easy for plant breeders to obtain the germplasm they need for their breeding programs. Of the 19 germplasm banks in the world, only CATIE, an agricultural research centre in Costa Rica, has the necessary treaties to permit it to share its library with other breeders (WCR, Jul. 2019).
Germplasm for coffee needs to be held as living plants because coffee seeds don’t remain viable for more than a couple of years when they are stored in seed banks.