Genomic analysis of Phytophthora infestans, which causes potato late blight, indicates that one particular strain contributed to the Great Famine in Ireland in the 1840s. An international team of researchers performed shotgun sequencing of 11 herbarium samples of infected potato and tomato leaves that were collected in continental Europe, Great Britain, Ireland, and North America between 1845 and 1896 that they then compared to 15 modern strains of P. infestans.
As the researchers report in a forthcoming eLife paper available at arXiv, their analysis implicated the HERB-1 genotype in the epidemic. That strain, they add, appears to have gone extinct, possibly due to increased resistance breeding in the plants. Previously, the US-1 strain had been thought to be behind the blight epidemic. The two strains, the researchers tell NPR, are closely related.
NPR adds that this work wasn't only an exercise in historical curiosity. "Potato blight is still a huge problem worldwide," Sophien Kamoun from the Sainsbury Laboratory in the UK tells NPR. "[It's] the third most important food crop in the world, and potato blight is the major constraint for growing potatoes."