The plant destroyer behind the Great Famine
The microbe that triggered the Irish potato famine has been identified from 150-year-old DNA.
Few crop failures have been as devastating as those caused by potato late blight in the 1840s. This disease is caused by a filamentous microbe called Phytophthora infestans, which spread from North America to Europe in 1845, leading to the Great Famine in Ireland and to severe crop losses in the rest of Europe. Phytophthora is thought to have originated in the Toluca valley of Mexico, where many different strains evolve alongside wild potato relatives, but the exact strain that caused the Great Famine, and how it is related to modern strains of the pathogen, has remained a mystery.
Kentaro Yoshida, Verena Schuenemann and colleagues used a technique called ‘shotgun’ sequencing to map the genomes of 11 historical strains of P. infestans and 15 modern strains. The historical strains were extracted from the leaves of potato and tomato plants that were collected in North America and Europe, including Ireland and Great Britain, from 1845 onwards and stored in herbaria for future research. By comparing the genomes of the historical and modern samples, Yoshida, Schuenemann and colleagues found that the historical strains all belonged to a single lineage that shows very little genetic diversity.
Previously it has been proposed that this lineage was the same as US-1, which was the dominant strain of potato blight in the world until the end of the 1970s, or that it was more closely related to modern strains than to US-1. Yoshida, Schuenemann and colleagues ruled out both of these possibilities and showed that the lineage that caused the Great Famine, which they call HERB-1, is clearly distinct from US-1. However, the two lineages are closely related, and so it’s likely that both HERB-1 and US-1 might have dispersed from a common ancestor that existed outside of Mexico in the early 1800s. Why US-1 later replaced HERB-1 as the dominant strain in the world is an important question for future studies.
To find out more
Listen to Sophien Kamoun and Hernan Burbano talk about genomics and potato famines in episode 1 of the eLife Podcast
Read the eLife research paper on which this eLife Digest is based: “The rise and fall of the Phytophthora infestans lineage that triggered the Irish potato famine” (May 28, 2013).
Read a commentary on this research paper: “Genomics: The early days of late blight”.
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Public Domain Dedication. The original “eLife digest” can be found in the linked eLife research paper.
