The fungal disease — called coffee leaf rust — is caused by the fungus Hemileia vastatrix, and it is decimating coffee crops throughout South and Central America, which accounts for most of the world’s production of tasty Arabica beans.
The fungal spores can survive for months and have no problem hitching a ride on wind currents or clothing and other items. But once the spores come into contact with a coffee plant leaf, they germinate and can penetrate the plant’s leaf within hours.
The first signs of infestation with the fungus usually show up as small, pale yellow spots on the upper surfaces of the leaves. These spots gradually increase in size – resulting in masses of orange urediniospores appearing on the underside of the leaf.
Photo taken: Sept. 23, 2010.
The fungus does not kill the coffee plant outright, so it must be a slow, painful death for the plant and the grower. As the leaves die and fall off, this reduces the number of nutrients the plant receives, leading to a feeble yield that gets worse as the disease spreads The plant basically chokes to death.
How serious is the coffee leaf rust? Latin America was hit with an epidemic of the fungus in 2012. Some farms lost 50 to 80 percent of their production, and the epidemic forced 1.7 million people out of work, according to the Global Coffee Report.
“The problem is not just the rust; it’s the rust and catastrophically low coffee prices,” says Stuart McCook, author of the upcoming Coffee is Not Forever: A Global History of the Coffee Rust. “It’s difficult for farmers to weather both.”
150 years ago, it wiped out an empire
We can go back to 1869 and the first time a global outbreak of the fungal disease was reported in Ceylon, in what is now known as Sri Lanka. This outbreak occurred just 10 years after the fungus was discovered by a British explorer around Lake Victoria in what is today Kenya.
At that time, Ceylon was the world’s largest producer of coffee, exporting over 100 million pounds of the beans to a thirsty world. Labor was cheap and market prices were high and the economy was flourishing — that is, until in the south-center of the island, small, pale yellow spots were seen on a few leaves of the coffee plants.
As the spores developed, they soon spread to other plants, and soon, the crop was decimated. Farmers tried planting their few healthy plants in other locations on the island, but wet, windy conditions — ideal for the spread of the fungal spores — didn’t waste any time attacking the new plants.
Ceylon hung on and fought the good fight, but by 1879, however, production began a rapid and steady decline. And so did value, as the market price of coffee plummeted.
That same year, London’s Royal Botanic Gardens at Kew sent an inexperienced, 25-year-old recent Cambridge grad named Harry Marshall Ward to Ceylon to study the disease. In his two years on the island, Ward was able to prove that the parasitic fungus H. vastatrix caused leaf rust and he even worked out the pathogen’s life cycle
While Ward’s work established his reputation as a plant pathologist and physiologist and although he was unable to stop the rust in the coffee plantations of Ceylon — he laid the foundations for solving the problem in the future. By 1890, 90 percent of the land under cultivation for coffee had been abandoned and the coffee crop disappeared from the island.
“Once coffee rust had broken out in Ceylon, the global epidemic was inevitable,” says McCook. By 1920, it had affected most of the coffee-producing countries in Asia and Central and East Africa.
The problem with the fungus
Even though we have known about the fungus that causes coffee leaf rust, we still don’t completely understand the darned thing. This means there is no cure for it and there is no meaningful, lasting method available to help farmers prevent the disease in their crops.
This is because Hemileia vastatrix is an obligate parasite. These parasitic fungi attack living organisms, penetrate their outer defenses, invade them, and obtain nourishment from living cytoplasm, thereby causing disease and sometimes death of the host. Obligate parasites, which require living cytoplasm and have extremely specialized nutritional requirements, are exceptionally difficult, and often impossible, to grow in a culture dish in a laboratory.
Researchers are now working to sequence the parasitic fungi’s genome and to understand its reproductive process, and this will take time. In the meantime, if a fungus isn’t bad enough to contemplate, coffee farmers have to worry about the F-1 hybrid coffee plants developed after the 2012 outbreak.
Most of the F-1 hybrids were supposed to be resistant to the fungus and other plant diseases. However, World Coffee Research (WCR) Scientific Director Dr. Christophe Montagnon told attendees at the Association for Science and Information on Coffee Portland conference on September 19, that this is not a permanent solution.
“Rust resistance coming from different sources of introgression — the transferring of genes from one species to another after hybridization and backcrossing — is being broken step by step,” Dr. Montagnon says. He added that it is only “a matter of time before rust resistance in most of the existing resistant varieties is going to break down.”
And the third problem coffee farmers are facing is global warming. A study in 2017 suggested coffee growing regions globally could shrink by 88 percent by 2050, due to climate change. The study was conducted by David Roubik, an entomologist and senior staff scientist for ecology, behavior, and evolution at the Smithsonian Tropical Research Institute in Panama.
He analyzed how climate change will affect coffee growers, and the results aren’t good. This is because coffee grows at specific temperatures, much like grapes. And we already know that grape producers are moving their crops to other locations. For coffee growers, this could mean either moving crops to higher altitudes or relocating to cooler places.
And that is not as easy as you might think. Roubik cites countries like Nicaragua, Honduras, and Venezuela that just aren’t mountainous enough to make this solution practical. “These regions “are less mountainous, so that coffee and bees have fewer options to move uphill,” Taylor Ricketts, the director of the University of Vermont’s Gund Institute for Environment and a co-author of the recent study.
Basically, there are two varieties of coffee: “robusta,” which as the name implies, is more robust and tolerates a wider range of soils and temperatures, and “Arabica,” which is way less tolerant. And we can add that Arabica is the variety of choice for most coffee drinkers, and that adds a bit of stress to the already stressful situation.
And while I hate doing this, we might as well get it out of the way – Pollinators, yes bees are also an issue. As the temperatures climb, bee populations will decline. “Our results suggest that coffee-suitable areas will be reduced 73–88 percent by 2050 across warming scenarios, a decline 46–76 percent greater than estimated by global assessments,” the study reads.
Enough said. I’m going to get a cup of coffee.
