Centuries of Potato Late Blight: Tracking Global Epidemics and Managing Future Outbreaks.

Phytophthora infestans killed the potato crop in Ireland in 1845, leading to widespread famine and the death of more than one million people. Historic herbarium specimens from the famine era were used to understand the pathogen's biology and track its global spread, providing a valuable resource for research. Historic outbreaks in the United States and Europe were caused by the FAM-1 lineage, whereas the US-1 lineage spread later. The famine lineage was basal in the phylogeny and ancestral to modern US-1, Mexican, and globally aggressive lineages. An admixture between the famine lineage and the Andean species Phytophthora andina was revealed, indicating a South American origin of the disease. Temporal changes in the presence and abundance of virulence genes were observed in historic compared to modern genomes. Expansion in effector abundance occurred as new genotypes emerged in the mid-twentieth century. Disease surveillance and genotyping on a global scale have helped to inform disease management.