Robusta and conilon cultivars

Four words that get used as if they were one

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Canephora

The species. Everything else on this page is a kind of canephora.

Robusta

Used two ways: loosely for the whole species, and in Brazil for one of the two botanical groups grown there, as distinct from conilon.

Conilon

The other group grown in Brazil, concentrated in Espírito Santo, where canephora arrived in the early 1900s. Breeders describe conilon plants as intermediate between the two wild African groups and presume the group arose from a cross between them before it reached Brazil. That origin is a presumption in the literature, not a settled finding.

Nganda and Erecta

Ugandan terms for two growth habits. Nganda plants are bushy and spreading. Erecta plants, which trace to seed brought from Indonesia in 1910, are upright, compact and earlier to bear. The two interbreed freely on Ugandan farms.

Two wild populations with opposite strengths

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Studies of canephora's diversity sort it into two primary groups named for where they grow wild. Plants of the Guinean group, from West Africa, are described as short, with close-set leaves, high in caffeine, small in the bean, early to ripen and resistant to drought. Plants of the Congolese group, from Central Africa, are described as tall and later ripening, with larger beans, intermediate caffeine and resistance to leaf rust, and as susceptible to drought.

Neither has everything a farmer wants, which is the standing argument for crossing them. The review of breeding programmes this page draws on makes a second point that matters as much: cultivated robusta everywhere descends from a small number of founder plants, most of them from Central and East Africa, so the forests the species comes from still hold variation that no breeding programme has used.

The variety catalogue assigns each of its robusta entries to a group, and the pattern follows the history. The Vietnamese and Indonesian clones it lists are filed as Congolese. The Brazilian ones are filed as crosses of the two groups. The Ugandan ones are given a group of their own.

Why nobody plants a single clone

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Arabica pollinates itself, so one arabica plant can found a uniform variety that comes true from seed. Canephora cannot. It has half arabica's chromosomes, two sets of eleven where arabica has four, and it is self-incompatible: a flower sets fruit only with pollen from a genetically different plant of a compatible type.

Two things follow. Seed from a robusta tree is a mixture, never a copy of its mother, so a selected plant is kept by taking cuttings, which makes it a clone. And a field planted to a single clone has nothing compatible to pollinate it. A robusta variety is therefore usually a set: several clones chosen to flower together and pollinate one another, released and planted as a group. The catalogue records this in what it calls each entry, a clone or a polyclonal variety, and the Brazilian programme describes releasing its clonal cultivars in sets for this reason.

The same biology explains the seed-propagated varieties. Vietnam's TRS1 is seed from a garden where four chosen clones pollinate each other; India's Sln. 1R is seedling progeny of two selected mother plants. They are cheaper to multiply than cuttings and less uniform.

What each country was trying to fix

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Indonesia

The first robusta breeding programme, begun in the Dutch East Indies. The review describes experiments with selection, inbreeding, cloning and grafting from 1907, and lists varieties released from 1920. It treated ease of propagation as a trait to select for and worked out the two-clone and many-clone seed gardens that other programmes later used. The catalogue carries four of its clones, among them BP 534 and BP 936, which the programme has since used as parents of newer hybrids.

India

Robusta was brought to Wayanad in Kerala from Indonesia in the early 1900s after leaf rust devastated arabica there. A later introduction from Sri Lanka, renamed Old Robusta, became the benchmark. The national institute then released three selections in sequence, Sln. 1R in the 1940s, Sln. 2R about two decades later and Sln. 3R in the 1970s. The first two were each released for better cup quality, bean size or evenness of yield than what came before, the third for cup quality and a more compact bush.

Vietnam

Introduced by the French in the early 1900s from the Congo, from Indonesia or both. Formal breeding began in the late 1970s at the research institute in the Central Highlands, aimed at varieties for that region. Its released clones, including TR4, TR9 and TR11, are described as rust resistant, high yielding and good in the bean. The review traces Vietnamese robusta to the Congolese group.

Uganda

A programme working with a native plant, since canephora grows wild in Uganda's forests. Selections from farms and forests were the country's planting material until the early 1990s, when coffee wilt disease, a fungus that has so far stayed largely within Africa, destroyed most of the varieties in common use. Breeding turned to resistance, and ten wilt-resistant clones followed: KR 1 to 7 in 2009 and KR 8 to 10 in 2017.

West Africa

Several West African countries are themselves home to wild canephora of the Guinean group. Ivory Coast, Ghana and Cameroon bred for yield, drought tolerance, resistance to local pests, plant shape and cup quality, drawing on material exchanged widely across Africa and from Asia. Their releases include both clonal varieties and seed-propagated hybrids.

Brazil

The review lists five institutions at work on the crop. Two have entries in the catalogue. The Espírito Santo state institute breeds conilon, and the review calls it arguably the most important conilon breeding institution in the world; its method takes twelve years from first selection to a released set of clones. The federal research corporation's station in Rondônia breeds both types for the western Amazon, and eight of its ten catalogued varieties are recorded as natural crosses between conilon and robusta plants, selected in farmers' fields, with the other two from controlled crosses. The priorities the review gives for Brazil include yield, even ripening, resistance to pests and diseases, tolerance of heat, drought and poor soils, and suitability for machine harvesting.

The robusta under an arabica tree

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Some canephora is grown for its roots alone. Where soil nematodes attack arabica, growers graft arabica onto a resistant robusta rootstock. Brazil's Campinas institute developed the clone Apoatã for this purpose, and it was used widely to bring coffee back to infested land in São Paulo, Minas Gerais and Espírito Santo. The variety catalogue lists a Central American rootstock, Nemaya, among its arabica entries for the same reason: nobody harvests it, but the trees above it would not survive without it.

How to read the catalogue's robusta entries

CoffeeHQ explanation

The table below is a selection from the 47 robusta entries in the World Coffee Research catalogue, chosen to show one or two from each programme. Three cautions apply to all of them.

The entries are the ones breeders supplied data for, so the list is a record of who took part and not a census of what is grown. The West African programmes described above have no entry at all. The disease ratings are categories given by each breeder for its own conditions, and are not directly comparable between countries. And where the catalogue quotes a yield for a clone, it is the breeder's trial figure, which the catalogue itself warns is not what a farm should expect; this page does not repeat those figures.

What the entries do show reliably is the argument of this page: that the word robusta covers plants of different ancestry, bred in different decades for different problems.

What to do next

• Robusta, the species — The plant itself: where it grows, its caffeine and its place in world production.
• Timor Hybrid — The natural cross that carried canephora's rust resistance into arabica.
• Espírito Santo — Where Brazil's conilon is grown and bred.
• Uganda — The country where robusta is a native plant.
• Become a coffee expert — A structured programme from the plant and its processing to roasting, water and tasting.