THE PROCESS IN MOTION

Why does a rust attack one coffee plant and not its neighbor?

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

▶ Play the process01A living catalog02An SH gene closes the door03A v gene opens it04More than fifty races05Nine genes, three species

A living catalog

The Coffee Rust Research Center (CIFC) is founded in 1955 at Oeiras, near Lisbon, in a country that does not produce coffee. Coffee plants and rusts from all over the world are brought there to be crossed systematically: in 1965, 2,101 coffee accessions and 783 rust samples, each kept alive on plants.

Read the stages without animation

1. A living catalogThe Coffee Rust Research Center (CIFC) is founded in 1955 at Oeiras, near Lisbon, in a country that does not produce coffee. Coffee plants and rusts from all over the world are brought there to be crossed systematically: in 1965, 2,101 coffee accessions and 783 rust samples, each kept alive on plants.
2. An SH gene closes the doorA race is defined by its attack profile on differential coffee plants, clones that carry known resistance genes, alone or combined. Race II, which attacks only arabicas without any particular SH gene, makes no pustule on a coffee plant that carries SH3.
3. A v gene opens itTo each resistance gene there corresponds a virulence gene in the fungus, v1 to v9. A race carrying v3 gets around SH3 and forms its pustule; a race is named by the genes it is able to get around. The grid in the drawing applies this rule to two example races.
4. More than fifty racesMore than fifty physiological races are described, 49 in Barka and coauthors in 2020. Race II is the most widespread in the world. The Peruvian samples of 2024 were read on 27 differentials.
5. Nine genes, three speciesNine dominant genes are identified: SH1, SH2, SH4 and SH5 come from Ethiopian lineages of pure arabica, SH3 from liberica, SH6 to SH9 from canephora. Outside arabica, the only sources have been liberica in India and canephora everywhere else.

To remember: A resistance is a lock: it holds until a race carries the key that answers it.

Read the full article and its sources ↓

Since the fungus exists as races, we need to know which ones, where, and which ones open what. That is the job of the Centro de Investigação das Ferrugens do Cafeeiro (CIFC), founded in 1955 in Oeiras, near Lisbon, in a country that does not produce coffee: a living catalog to which coffee plants and rusts from all over the world are brought and in which they are systematically crossed with one another.

In 1965, the center had assembled 2,101 coffee accessions and 783 rust samples, each kept alive on plants, race by race. A race is defined by its attack profile on a series of differential coffee plants carrying known combinations of resistance genes.

McCook 2019, p. 132-133; LC ch. 13 and 16

Nine dominant resistance genes have been identified, SH1 to SH9. SH1, SH2, SH4 and SH5 come from Ethiopian lineages of pure arabica, SH3 from Coffea liberica, SH6 to SH9 from Coffea canephora. The CIFC differential clones carry them alone or combined; to each resistance gene there corresponds a virulence gene in the fungus (v1 to v9), and a race is named by the genes it is able to get around.

More than fifty physiological races have been described (49 in Barka et al., 2020); race II, which attacks only arabicas with no particular SH gene, is the most widespread in the world. The Peruvian samples of 2024 were read on 27 differentials. The only sources of resistance available outside arabica have therefore been two related species: liberica in India, canephora everywhere else.

Silva et al., Coffee Leaf Rust Resistance: An Overview (Springer, 2022); “An overview of physiological specialization of coffee leaf rust”, Agronomy Journals 2 (2019); BSPP 2022, p. 18; Quispe-Apaza et al., Agronomy 14 (2024), 1811; LC ch. 13