July 2022

Last month we talked about the impact that climate change is having on coffee and some of the research that came out earlier this year predicting land suitability for coffee growing. This month we are looking at the seed research and varietal selection that is happening on the farm and in research, including at the Royal Botanic Gardens, Kew.

different varieties of coffee cherries, Pacamara are large and are shown here are red and yellow varieties. Bourbons are smallish and come in yellow, orange and red.  Also shown are Maragojipe (large and red) Moca (small, round and red) and F10 (medium sized and a deep red shade)

In April last year Dr Aaron Davis – Senior Research Leader of Crops and Global Change at Kew – published a paper with D. Mieulet, J. Moat, et al, in Nature Plants (Issue 7, April 2021 Arabica-like flavour in a heat-tolerant wild coffee species) outlining that a recently rediscovered varietal was being researched for its potential climate resistant properties. The varietal is Coffea stenophylla, and it was re-found in West Africa in 2018. It had been grown there commercially until the 1920s and was thought to be extinct in the wild so the discovery is exciting. It is also exciting as the number of commercially viable types of coffee is so small that the gene pool for research on how to adapt coffee for the future is tiny. Any additional discoveries are helpful.

There are two species of coffee that have wide commercial success – Coffea arabica and Coffea canephora. Canephora is commonly known as Robusta, named for its resistance to disease, higher temperatures and drought. Arabica, long considered to be superior in flavour, is less resilient and requires a very specific temperature range and rainfall. With a warming climate and unpredictable precipitation, Arabica will struggle. Enter Stenophylla. Stenophylla prefers temperatures around 6.5°C higher than Arabica and shows drought and some coffee leaf rust resistance. And, unlike Robusta, it is considered to have an Arabica-like flavour profile. Unfortunately, it isn’t as productive as Robusta or Arabica which is why it wasn’t grown more widely and almost disappeared 100 years ago. However, with modern growing techniques and limited climate-resistant options, Stenophylla may yet have its day.

The team at Kew led by Dr Aaron Davis have been researching historic varietals like Stenophylla and investigating how they may help productivity and coffee quality in the future. On the farms the aim is the same but the method more immediate.

Most farms have areas of land and trees that produce more or better quality. For propagation, farmers select seed from their own best-performing trees and they will buy seedlings from research centres when there is a new development. Over the last decades, seed selection has focussed on cup quality and resistance to today’s problems – coffee leaf rust for example. As they face more uncertainty, farmers are selecting more for general hardiness and resilience, taking the best performers across several criteria and applying them to the farm. Some farmers are removing varietals planted for their curiosity factor a few years ago and are returning to first principles – planting for their own microclimate, soil type, soil texture, and light availability.

In some areas, seed selection and propagation are being supplemented by good old-fashioned grafting. Done widely with apples in the UK, this is a time-honoured method of splicing more fragile varietals onto hardier plants that suit the local environment. In coffee, Robusta with its strong root system and ability to extract nutrients from difficult places is the base plant often used. Different cultivars of Arabica are grafted onto an established Robusta and grow from there. In the future we may be grafting onto Stenophylla as it is thought to be potentially more resistant to climate problems than Robusta.

For all its warming goodness and encouraging stimulation, coffee has very particular requirements to produce its best quantity and quality. As these absolutes are less guaranteed now, farmers and researchers alike will be continuing their investigations into what makes a coffee tree happy in our future world.

Monmouth x