We eat a lot of potatoes in our house.  Having a vegetarian and meat-eater in the house can make mealtimes stressful, but baked potatoes topped with broccoli for me and bacon for him makes us both happy.  I kid, but in early nineteenth century Ireland potatoes were no joke… they were the staple food for the lower class, the landless laborers.

Existing dependent on a single food source is risky and in 1845 a plant disease epidemic took out the potato in Ireland (in the field and in storage).  The disease would later be named late blight and is regarded as the disease that birthed the study of plant pathology.   The causal agent of late blight is a Phytophthora infestans (Latin for “plant destroyer”), fungal-like organism called an oomycete.  As a result of this microscopic killer, an estimated 1 million Irish starved and another 1.5 million emigrated from Ireland, dramatically changing not only Ireland but countries like the United States that received the displaced.  Late blight remains a significant threat to potato and tomato industries today (2009 epidemic in Northeast US); however, we now have management options such as fungicides and moderately resistant varieties to minimize losses.

Potato with late blight (foreground); Potato treated with fungicides (background)

Potato with late blight (foreground); Potato treated with fungicides (background)

(Image: Courtesy D. Inglis via apsnet.org)

Last week, Yoshida et al. (2013) released a study identifying the specific strain (or genotype) of P. infestans responsible for the Irish Potato Famine. Researchers isolated samples of the pathogen from preserved potato leaves with late blight symptoms and compared them to modern strains with DNA analysis.  Genotype HERB-1 was consistently isolated from the historic Irish samples, suggesting it was the strain responsible for the late blight epidemic.  HERB-1 is different from modern genotypes and is likely extinct, having been replaced by US-1 by the 20th century, as the predominate genotype outside of P. infestans center of origin (Mexico).  Researchers also note that while US-1 and HERB-1 are related, US-1 is not a direct ancestor of HERB-1.

I think one of the most interesting parts of this study was the use of preserved herbarium samples to generate the dataset.  Just think of other pathogen populations and histories that could be elucidated using this approach!  Aside from the cool factor, understanding how these pathogens evolve is vital for developing new management strategies.

 PS – For more on late blight click here.