The fungus Phytophthora infestans (Irish potato famine of 1845-1849) caused one million deaths, up to two million refugees, and a century-long population decline in Ireland. Today, P. infestans remains a threat to potato production worldwide. In 2013, Thomas Gilbert and others at the University of Copenhagen sequenced five 19th-century European strains from archival herbariums – including the oldest-known European specimen (1845). Comparisons with modern strains illuminated the fungus’s migratory story and revealed P. infestans as an aggressive pathogen, mutating quickly to overcome fungicides and the breeding of resistant potato crops.
Did you know? Ireland’s disproportionate dependency on the Irish Lumper potato variety reduced genomic diversity of the crops and contributed to the devastation.