Figure 1A. Late blight lesion on potato foliage Figure 1B. Lesion as seenthrough a dissecting microscope Figure 1C. Micrograph of sporangia Disease Cycle Click on any picture to see the enlarged image. In most of the United States and Canada, Phytophthora infestans requires a living host to survive between seasons. Infected tubers that are planted or cull tubers that survive the winter may be sources of the pathogen that initiate epidemics the following season. Sporangium from which a zoospore is germinating.
Infections are visible as small lesions after three to four days.
Sporulation may occur on lesions that are only four to six days old. Potato leaflet with older lesion that is not sporulating. Tomato fruits infected with P. infestans . Green Tomato fruits. The pathogen is sporulating from the infected fruits.