Potato blight on leaf. Coloured scanning electron micrograph of potato blight sporangia emerging from a potato leaf. Potato blight is caused by the fungus Phytophthora infestans. Here, sporangia (reproductive branches) of the fungus are seen emerging from the stomata of the leaf. The first widespread infection of commercial importance was in 1845, when most of Europe suffered decimated potato crops due to blight. Prevention of blight depends on spraying and, increasingly, on selective breeding. Magnification: x400 at 6x4.5cm size.