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The Artful Amoeba

The Artful Amoeba

A Blog About the Weird Wonderfulness of Life on Earth

Chocolate Frosty Pod Rot and You

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Coffee drinkers recoiled in horror when news that their favorite plant had come under serious attack by a fungus called rust this year. The news came close on the heels of news that the bacterial disease huanglongbing is devastating the Florida citrus industry, driving up prices and threatening quality. As a faithful o.j. drinker, I was not happy to hear about this myself. But there's one crop for which I've long dreaded hearing similar news: Theobroma cacao, bringer of chocolate. That day, sadly, has come.

This week I am at the American Phytopathological Society/Mycological Society of America joint meeting in Austin, Texas, scouting for story and blog post ideas and reconnecting with my former teachers and classmates from Cornell. There is indeed a lot of talk here about huanglongbing and the scurrilous psyllids who spread it. But to my horror, I discovered in the poster session that there is also a disease (actually, two or three) of cacao well-poised to harm the chocolate industry: frosty pod rot of cacao. Here it is:

These are cocoa pods on the cacao tree. Inside are the beans/seeds/nibs that get roasted to make cocoa and chocolate. These pods, however, are never going to see the inside of a Hershey's factory. From Alme and Phillips-Mora 2005. Click image for source.

Let's first take a moment to savor this name. Frosty Pod Rot is one of the best I've seen. It starts out like an obnoxiously sweet breakfast cereal (and the effect is only heightened if you add "chocolate" to the front) and ends in a disgusting mass of fungi and macerated plant tissue. Unlike the human public health community, which has abandoned such eloquent and haunting names as "consumption", "malaria", "yellow fever" and "whooping cough" in favor of horrible acronym soups like SARS, AIDS, and MERS, plant pathologists have kept up the tradition of descriptive disease naming. I am a huge fan. Most are more straightforward: black leg of canola, or late blight of potato (cause of the Irish Potato Famine), for instance. But we also have huanglongbing (literally, "yellow dragon disease"), fire blight, powdery mildew, sooty mold, witches' broom, or as I learned this week, the new disease "funky flower" of cranberry (whose causal pathogen is still unidentified, but early evidence indicates may be a virus). Keep up the good work, plant pathologists.

Frosty pod rot -- both the disease and its handle -- have been with us for a long time. It made its debut in the late or possibly early part of the 19th century. The fungus eats the inside and outside of cocoa pods and leaves them a total loss. Here's a close-up:

Conidia (asexual spores) and filaments of Monilophthora roreri, the fungus that causes frosty pod rot. Note the chains in which the simple spores are produced. Creative Commons Ronnydv10. Click image for license and source.

For a long time frosty pod rot was relatively confined to Colombia, Ecuador, and western Venezuela in northwest South America. Since the 1950s, it has spread throughout South and Central America, reaching Panama in 1956, Costa Rica in 1978, Nicaragua in 1980, Peru in 1988, Honduras in 1997, Guatemala in 2002, Belize in 2004, and Mexico in 2005. It can cause growers to abandon entire cacao plantations, as losses in infected groves can near 100%

Frosty pod rot, along with its close relative witch's broom of cacao, together have devastated cacao-farming regions in these countries, and "are responsible for the plummet in tropical American cocoa production," according to a 2005 article in Mycologia. That sounds bad. At least one scientist, according to the authors of the Mycologia article, believes that M. roreri is "still in an invasive phase ... and is poised to devastate already crippled production in Bolivia and Brazil, once it arrives in those countries." Apparently, that is still true in 2013, as the poster that I discovered this pathogen on stated that frosty pod rot is still a "serious threat" to cacao plantations in Bolivia and Brazil, and even West Africa.

Plant pathologists don't just exist to give plant diseases kick-ass names -- they also exist to help farmers stay in business, keep food affordable for the rest of us, and to prevent catastrophes like famine or the functional loss of entire crop species or cultivars (see the Gros Michel banana and Panama Disease for a premier example). Clearly, they also exist to keep us all well supplied with chocolate. As much as I love frosty pod rot the concept, I do not love frosty pod rot the disease. Keep fighting the good fight, plant pathologists, and let's hope the day that frosty pod rot hits the front page of the New York Times is still a long way off -- or never comes.

Reference

Aime M.C. & Phillips-Mora W. (2005). The causal agents of witches' broom and frosty pod rot of cacao (chocolate, Theobroma cacao) form a new lineage of Marasmiaceae, Mycologia, 97 (5) 1012-1022. DOI:

The views expressed are those of the author and are not necessarily those of Scientific American.

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