Similar fungus disease shows there is no quick remedy

A.M. Costa Rica archive Contemporary engraving shows the desperation of an Irish family evicted from their home at the height of the potato famine.

Many similarities exist between today’s epidemic of coffee blight and the Irish Potato famine in the 1840s. Both today’s coffee plants and the 19th century Irish potatoes lack genetic diversity.

Cornell University researcher Phil Arneson notes that nearly all the coffee in commercial production when rust appeared in the Americas, could trace its lineage to a single tree planted in the conservatory of King Louis XIV in 1713.

So, too, did an estimated third of the Irish population depend on a potato variety that is known as the lumper. This variety did well on poor Irish soil but it was highly vulnerable to the potato blight, Phytophthora infestans.

Thanks to the politics of the time and this form of monoculture, the cost to Ireland was 1 million dead from famine and millions more emigrating elsewhere. The country has not really recovered.

Potato blight continues to be a serious problem, although agricultural practices and spraying can battle the spores.

The situation is more complex with coffee. The plants grown here are of the arabica species, which is known for its taste that is in high demand.  The species also seems to be highly vulnerable to blight. Coffea canephora, therobusta coffee that is forbidden in Costa Rica, contains most of the resistant commercial species. Robusta is considered a lower grade coffee with a bitter taste. There are about 25 other coffee species that have not been studied well, according to a research report by Arneson.

A recent National Public Radio report in the United States addressed the efforts by the Center for Tropical Agricultural Research and Education in Turrialba to find resistant species.

In both potato blight and coffee rust, Hemileia vastatrix,the disease is caused by fungus spores entering small openings in the leaves and then propagating.

The orange coffee rust causes the plants to shed leaves and either kills the host or reduces the yield. Potato blight appears as purple blotches on the leaves, and it can infect the potatoes underground. Scientists are still trying to find a resistant potato of high commercial value. And even if they do, the blight may evolve to defeat the resistance. The same is truewith an potentially resistant coffee variety.

Both pathogens are spread by the wind and rain. There is some debate in coffee circles whether shade-grown plants are less susceptible to the rust. Some scientists say that growing coffee grown in full sun can reduce the infestation spores like wet leaves.

While scientists seek genetic answers, growers are encouraged to use aggressive management to reduce infestation by spraying, pruning infected branches and fertilizing to keep plants healthy, as Arneson noted.

As with potato blight, the disease is likely to be around for a long time.

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