Infestans

Peronosporeae De Bary published his first work on fungi in 1861, and then spent more than 15 years studying Peronosporeae, particularly Phytophthora infestans (formerly Peronospora infestans) and Cystopus (Albugo), parasites of potato.

Disaster struck in August 1845, when a killer fungus (later diagnosed as Phytophthora infestans) started to destroy the potato crop.

The origin of the pathogen has been traced to Toluca Valley of Mexico, Neiderhauser, JS 1991 Phytophthora infestans: the Mexican connection pp 25–45 Symposium of the Mycological Society.

When Phytophthora infestans arrived from the Americas in 1845 to Ireland, the lumper had no resistance to the disease leading to the nearly complete failure of the potato crop across Ireland.