Outbreak of coffee rust threatens Latin American coffee supply

A fungus outbreak is threatening to wipe out Latin American coffee crops and trigger a global coffee crisis.

According to the American Phytopathological Society, coffee rust is a disease caused by the fungus hemileia vastatrix, which is characterized by half-smooth spores.

Infections usually start on the lowermost leaves of a coffee plant, where the fungus protrude through the stomata on the undersides of leaves.

The disease causes powdery yellow-orange lesions to appear on the bright green leaves, making them turn a brownish yellow tinge. These lesions produce more spores, which spread by wind or rain to infect others.

Though the fungus doesn’t kill coffee plants, it debilitates them by causing leaves to fall out. With its nutrition source gone, the plant is unable to produce coffee cherries.

Coffee rust currently has no cure, and while copper-based fungicides have proven effective in controlling infection, chemicals can accumulate and become toxic to the environment.

Scientists have also turned to genetic resistance, cross-breeding the rust-susceptible Arabica with a natural hybrid immune to the disease to create a more rust-resistant variety.

The resulting beans, though not as high quality as the Arabica, were at least good enough to be accepted by growers and buyers, according to the BBC.

However, the World Coffee Research has warned that the fungus is evolving, and may overcome once-immune genes in five to ten years. As of 2017, the Honduran Lempira was no longer resistant, and the natural Timor Hybrid’s resistance is also breaking down.

Coffee rust had previously wiped out crops in present-day Sri Lanka during the late 1800s. But while that region bounced back by switching to tea production, it’s unlikely Latin America will be able to do the same.

1. Hemileia vastatrix spores
2. Spores infecting a coffee bean leaf
3. Fungus infecting leaf
4. Fungus spreading through coffee plant
5. Fungus developing new spores
6. Fungus spores transferred to other trees
7. Half of leaves disappear
8. Coffee cherries deprived of nutrition, plant loses ability to grow new cherries
9. Fungicides effective in controlling rust, but can be toxic to environment
10. Arabica cross-bred with rust-resistant variety to form hybrid
11. Fungus evolving, could break down rust resistant varieties in 5 to 10 years

American Phytopathological Society, Chemical & Engineering News, BBC, CNN, NPR