F1 hybrids

Why the parents are chosen to be unlike each other

CoffeeHQ explanation

Most cultivated arabica is closely related. A cross between two ordinary varieties joins two very similar sets of genes. A cross between a cultivated line and a wild or landrace Ethiopian plant joins two sets that have been apart for a long time, and first-generation offspring of such a cross commonly grow more vigorously and yield more than either parent. Breeders call the effect hybrid vigour.

It also lets a breeder combine traits that rarely occur together. One parent brings what decades of selection built: compact stature, high yield, resistance to rust. The other brings diversity from the species' homeland, which is where the catalogue locates arabica's highest cup quality.

What has actually been measured

Sourced

The catalogue states that F1 hybrids tend to have significantly higher production than non-hybrids. For Centroamericano, a cross of the Sarchimor line T5296 with the Ethiopian landrace variety Rume Sudan, it reports production increases of 22 to 47 per cent over the standard varieties of Central America in breeding evaluations. It rates Centroamericano's quality potential at high altitude as very good, while the text of the same entry speaks of exceptional cup quality potential when the variety is well managed at high altitude.

The published account of Starmaya by its breeders reports the same general pattern: in trials, F1 hybrids showed higher yield and vigour than conventional cultivars. Those trials were run by the people who made the varieties, in a limited number of sites. They establish that the effect is real; they do not tell a farmer what to expect on a particular hillside.

The catalogue adds cautions of its own. Centroamericano may have difficulty establishing roots in its first two years and needs careful nutrition while it does.

Why saved seed does not work

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1. Every F1 plant has one set of genes from each parent. That is what makes the generation uniform: all the plants got the same two halves, so they look and behave alike.
2. Its own seed reshuffles those halves. When an F1 plant sets seed, the two parental sets are mixed afresh in every seed. The catalogue calls this segregation.
3. The next generation scatters. Some seedlings resemble one grandparent, some the other, most something in between. The catalogue warns of losses of yield, disease resistance, quality and other traits.
4. So new plants must be made again from the parents. Either by repeating the cross by hand for every batch of seed, or by cloning an F1 plant in a laboratory. Both are slow and costly, which is why these varieties are sold as nursery plants.

The catalogue's advice to farmers is to buy F1 seedlings only from trusted nurseries.

The one that can be grown from seed

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Starmaya is the exception, and how it came about shows the problem clearly. If two fertile varieties are simply planted together, most seed comes from each variety pollinating itself, because arabica does. Only some is the hybrid. As early as 1998 breeders saw that this could be avoided if one parent produced no pollen at all: every cherry on that parent would then have to be a cross.

In 2001, researchers working on a farm in Nicaragua noticed such a plant, a male-sterile arabica growing among a collection of wild Ethiopian and Sudanese coffees. They crossed it with Marsellesa, a rust-resistant Sarchimor. The result performed well in field trials and was released as Starmaya, which the catalogue describes as so far the only F1 hybrid that professional seed producers can propagate by seed.

It is not perfectly uniform. The catalogue notes that around 15 per cent of plants will differ in appearance or performance from the standard.

An older hybrid that is rarely called one

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The catalogue files Ruiru 11, released in Kenya in 1985, in the same genetic group as the Central American hybrids. Its seed is made by hand-pollinating compact Catimor mother plants with pollen from a complex tall male parent, and what farmers receive is a mix of first-generation siblings.

The table below therefore spans two programmes a quarter of a century apart, one in East Africa and one in Central America, that arrived at the same method for the same reason: no single stable variety held all the traits they needed.

What the label does and does not tell a drinker

Tendency, not a guarantee

The catalogue rates most of these hybrids very good for quality potential at high altitude and one, Casiopea, exceptional. Those are ratings of potential under good management at the right altitude. The catalogue also notes that these varieties are relatively new, that only a handful have become commercially available, and only in some countries.

For a drinker the practical meaning is modest. A named F1 hybrid on a bag identifies a known cross from a known programme, which is more than most variety labels can claim. It does not predict flavour, and CoffeeHQ has not tasted any of them.

What to do next

• Sarchimor — The group that supplies one parent of most of these hybrids.
• Ruiru 11 — The Kenyan variety made the same way since 1985.
• Timor Hybrid — Why the introgressed hybrids carry robusta genes.
• Species and varieties — Where hybrids sit among mutations, selections and landraces.
• Become a coffee expert — A structured programme from the plant and its processing to roasting, water and tasting.