March 17, 2008

It's St. Patrick's Day, So Let's Talk Blight

Being that today is the day when everybody is supposed to be a little bit Irish, it's a good day to remember how an organism that was until fairly recently classified as a fungus once changed Ireland, America and the world. I'm talking about Phytophthora infestans which, in fairness, isn't actually a fungus but an oomycete. Oomycetes, unlike fungi, don't have a chitinous cell wall and there are some other differences as well. Still, just as non-Irish people are today a little bit Irish, let's play along and say that oomycetes are a little like fungi.

Phytophthora infestansPhytophthora infestans is the pathogen that caused the Irish Potato Famine of the 1840's that led to a wave of Irish migration to the United States. Many Irish-Americans can trace their ancestry back to an emigrant who left Ireland precisely because of the blight which, in turn, caused the collapse of not only the Irish economy but the British as well due to some very ill-advised speculation in grain futures. What those emigrants didn't know was that they were actually traveling back along the path by which P. infestans had gotten to Ireland in the first place. The population of the organism that caused the blight was native to America; it had already triggered the destruction of potato crops throughout the eastern US. From here, it traveled aboard a shipment of potatoes to Belgium and proceeded to demolish potato crops in that country and the Netherlands before finding its way to Ireland and triggering greatest wave of emigration from that country in all of its history.

For those who would like to read more about the specifics of how the Blight reached Ireland, today's New York Times is running a column entitled "The Fungus That Conquered Europe" (warning: registration is necessary to read the piece).

Of course, Phytopthora is a genus still very much with us. In recent years, close relatives of the potato famine pathogen have also damaged citrus crops in Florida with root and crown rots and are also responsible for sudden oak death and, to a lesser extent, are pathogens of a great number of vegetable crops. There are other parallels in the modern world to the Irish famine of the 1840's, too. As I've noted previously, the Ug99 strain of Puccinia graminis poses a major threat to world wheat crops and the rice blast fungus, Magnaporthe grisea, is a major pathogen with enough genetic variability around the world to pose an ever-looming threat as well.

Victims of Phytophthora infestans, c. 1845Despite my nom d'blog, I'm not actually Irish — not even a little bit. Considering how much something like a fungus affected Ireland less than two centuries ago and how much that something changed the face of America forever, too, it's a good day for a bit of mycological reflection. For most of us, fungi aren't something we give much thought. Until they affect us by taking food off our tables or eating through the walls of our homes, fungal pathogens really don't get much opportunity to escape into conscious consideration. They could at any moment, though, change our lives forever. They've certainly done so before.

St. Patrick may have driven the snakes out of Ireland according to legend, but he doesn't seem to have been very good against Phytophthora. Still while you're hoisting a green beer at O'Malley's Pub today, keep in mind that a few errant cells from the right fungus can do a lot more than ferment what's in your mug; they can also foment massive changes in the course of human history.

Happy St. Patrick's Day to all.

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