Phytophthora blight
from the root to the foot, but direct infection of the foot also occurs. Exudates leaking from growing root tips promote germination and attract the zoospores [...] fungal growth on the leaves. The centre is grey-brown with a light-green edge. On the stem, elongated brown lesions occur, usually circling the stem. On potato [...] through the skin. The Great Famine was a period of mass starvation caused by this disease which ravaged potato crops throughout Europe during the 1840s.