347 - A new history of coffee
Coffee now represents the primary source of wealth of many tropical countries. Only two species are cultivated, which produce the renowned Arabica and Robusta. However, a total of nearly 120 wild Coffea species exist which, starting from their origin in Lower Guinea, colonized the whole of Equatorial Africa and the Madagascar region in 400 000 years. That has been found by a recent study by IRD researchers and their Brazilian partner 1, using DNA sequencing of 26 species. Up to now, owing to the presence of coffee bushes in Africa, Madagascar and India, botanists thought that they originated from the Horn of Africa, before the Gondwana supercontinent broke up, more than 100 million years B. P. These investigations prompt a reorientation of research onto the coffee genome, with a view to improving this plant so highly important in agronomic and socio-economic terms.
Once upon a time there was a young shepherd called Kaldi, who found his goats unusually agitated after grazing on the red fruit of a shrub which was unknown to him. Coffee was thus said to have been discovered in this way in Ethiopia in the VIIIth Century. However, the legend does not say that, well before it was cultivated in over 50 tropical countries, Coffea shrubs arose in Lower Guinea, in Atlantic Central Africa. This was shown recently by IRD researchers and their Brazilian partner 1 in a study on the origin, diversification and expansion of wild coffee plants.
The origins of coffee
With around 120 known species, the taxonomy of coffee bushes is complex. As François Anthony, director of research at the IRD and co-author of these investigations remarks “Very few studies have been done on their phylogeny up to now . That remained poorly defined. ” DNA sequence analysis on plastids of 26 different species of the genus Coffea , led him and his team to identify two separate evolutionary lines, or clades: one that can be traced over the whole present area of distribution of coffee, from West Africa over to Madagascar, and another which occurs only in Lower Guinea. That region, known for its floral richness, shows the greatest diversity in DNA sequences. It is therefore a major centre of speciation 2 for Coffea . It is thus Lower Guinea and not Kenya, implicated by the hypothesis postulated in the 1980s, where the cradle of these shrubs would be found. “The current distribution of coffee in Africa, Madagascar and up to India suggests the presence in East Africa of ancestral forms, which would then have been isolated by the break-up of the Gondwana supercontinent, 100 million years ago ”, the geneticist explains.
A very recent history
The research team has completely overturned this chronology: the origin of these plants goes back only 400 000 years. The scientists defined a molecular clock to estimate the age of Coffea by use of DNA sequences of a species of a related genus (Rubia ), whose origin is dated at the Upper Miocene. They thus calibrated the time scale for the evolution of coffee and reconstructed its history. This is the first ever attempt at dating their origin.
Coffee’s taxonomic explosion
Over the past 400 000 years, the Earth’s climate has been marked by a succession of cycles of glaciation/deglaciation about every 100 000 years. These have induced a high variability in climate and intense phases of cooling which are expressed by more severe drought as far as the Equator. During these arid periods, the flora has survived in regions suitable for forests, known as “refuge zones”, often situated at altitude or near oceans, such as Lower Guinea. These regions are now known as biodiversity hot spots. Conversely, during the interglacial periods, warmer and more humid, the tropical forest and its flora spread. “Coffee bushes experienced a wave of dispersal which enabled them, from their area of origin, to colonize all the types of forest in equatorial Africa and in the Madagascar region, from the sempervirent, “always green”, forests, to the gallery forests, surrounded by savannah” , explains François Anthony. The species then diversified: “in the course of their recent history, the African forests have undergone a real radiative 3 explosion of coffee plants ”, the researcher comments.
Coffea species are bushes of the underwood, and therefore particularly threatened by environmental changes. In this respect, they give evidence of disturbances undergone by the tropical forests during the past 400 000 years, notably in response to climate changes. Research on them should help trace back the history of the forests.
Given the very recent evolution and the speed of their diversification and dispersal, there is little difference between the genes of one species of coffee and another, but considerable difference in the level of their expression. “The conclusions of our study are therefore being redirected towards the genetics of the coffee bush, with a view to improvement of this plant which is of great importance in agronomic-and socio-economic terms ”, concludes François Anthony. Its genome is undergoing sequencing by the IRD scientists and their partners 4.
1. This work was conducted by scientists of the research unit “Résistance des plantes aux bioagresseurs” (UMR IRD / Université Montpellier 2/ CIRAD) in conjunction with the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico of Brazil.
Rédaction DIC – Gaëlle Courcoux
Translation - Nicholas Flay