THE PROCESS IN MOTION

Why cross the two halves of canephora?

Start the scene or choose a stage. The animation simplifies the mechanism; what follows gives the details and the available references.

▶ Play the process01Two wild groups02Two opposite trees03Crossing the two halves04One more round

Two wild groups

In the 1980s, Berthaud distinguishes two large sets, named after the regions where the wild populations grow: the Guinean group, in Upper Guinea, and the Congolese group, in Lower Guinea and the Congo basin. Genetic markers tie this structure to the forest refuges of the glaciations, where isolated populations diverged each on its own side.

Read the stages without animation

1. Two wild groupsIn the 1980s, Berthaud distinguishes two large sets, named after the regions where the wild populations grow: the Guinean group, in Upper Guinea, and the Congolese group, in Lower Guinea and the Congo basin. Genetic markers tie this structure to the forest refuges of the glaciations, where isolated populations diverged each on its own side.
2. Two opposite treesThe Congolese is tall, with long internodes, little branched, late, resistant to rust, with large beans and intermediate caffeine, but sensitive to drought. The Guinean is short, with tight internodes, early, drought-resistant, with small beans rich in caffeine.
3. Crossing the two halvesIn Côte d'Ivoire, the CNRA built reciprocal recurrent selection on this opposition: systematically crossing Guineans and Congolese, retaining the best hybrid progenies, then starting again from them. One is not looking for the good tree, one is looking for the good parents.
4. One more roundThe gain has been measured: yields 16 to 140% above the average of two commercial clones. The heritability of yield, the share that is really passed on to the offspring, is 0.25 to 0.45 over four years: progress is real, but it is earned generation after generation.

To remember: The defects of each group are the qualities of the other: their cross is the method, not an accident.

In history: Cirad's ROBUST project extends the Ivorian program, aiming at climate change.

Read the full article and its sources ↓

The structure of the species was read twice: first in the field, by eye, then in the DNA. The two readings agree, which is rather reassuring.

In the 1980s, Berthaud proposes distinguishing two large sets, named after the regions where the wild populations grow. On one side Upper Guinea: the “Guinean” group. On the other Lower Guinea and the Congo basin: the “Congolese” group.

In 2000, Montagnon subdivides the Congolese group into four. SG1, on the Atlantic coast of Central Africa, from which the Brazilian Conilon comes. SG2, in the Congo basin, which is Robusta in the strict sense, the one planted all over the world. B, for the rest of the basin. And C, for the Central African Republic and Cameroon.

Then genetic markers take over, and they add an explanation that the field could not give. Microsatellites, in Gomez in 2009 and Cubry in 2013, tie this structure to the forest refuges of the glaciations: when the forest fragmented, populations became isolated, and each diverged in its own corner. Recent human migrations did the rest.

The 8,580-SNP chip of Mérot-L'Anthoëne, in 2019, refines the picture further. A SNP is a position in the genome where a single DNA letter changes from one tree to another. Reading 8,580 at once separates populations that earlier markers confused.

The subgroups are designated by letters, and each is tied to a region.

• AGabon, Congo and western DRC.
• EDRC.
• CCameroon.
• BEastern Central African Republic.
• OUganda.
• GAngola.
• RSouthern DRC.

Gomez et al., BMC Evolutionary Biology, 9:167, 2009; Cubry et al., Genetic Resources and Crop Evolution, 2013; Mérot-L'Anthoëne et al., Plant Biotechnology Journal, 2019; Kawuki et al. 2026, introduction; level: peer-reviewed journals, read through their abstracts and through the 2026 review

The two large groups have opposite phenotypes that breeders exploit. The Congolese is tall, with long internodes, little branched, late, resistant to rust, with large beans and intermediate caffeine, but sensitive to drought; the Guinean is short, with tight internodes, early, drought-resistant, with small beans rich in caffeine. The Conilon behaves like an intermediate, which has led to the supposition of an ancient hybridization between the two.

Kawuki et al. 2026, introduction; Gomez et al. 2009; atlas sheets

The Ugandan populations form a separate group, established by Musoli (2009) and confirmed by Kiwuka (2021): on 18 markers, they fall into none of the known groups. Two forms coexist there, the Nganda, with a spreading habit and weak stems, considered to come from the local forests, and the Erecta, with an upright habit, strong stems and large cherries, which the literature derives from Javanese seeds received in 1910.

Kawuki et al. 2026, introduction and § 2.4; Musoli et al., Genome, 2009 (doi 10.1139/G09-037); Kiwuka et al., PLoS ONE, 16 (2), e0245965, 2021

In Côte d'Ivoire, the CNRA built a method on this opposition, reciprocal recurrent selection. The principle: systematically cross the Guinean and the Congolese, retain the best hybrid progenies, then start again from them for the next round. One is not looking for the good tree, one is looking for the good parents.

The gain has been measured. Leroy and his coauthors (1997) report yields 16 to 140% higher than the average of two commercial clones. Montagnon (2003) puts the narrow-sense heritability of yield between 0.25 and 0.45 over four years, that is, the share of yield that is really passed on to the offspring. A middling value: progress is real, but it is earned generation after generation.

It is the only program in the world to have organized the meeting of the two halves of the species. Cirad's ROBUST project extends it, aiming this time at climate change, through agroforestry and through the diversity of genetic resources.

Kawuki et al. 2026, § 2.5 and 2.7.2, citing Leroy et al. 1997 and Montagnon et al. 2003