Over the 150 years that separate us from the first epidemic of potato late blight in Europe and the onset of phytopathology as a science, Phytophthora infestans (Mont.) de Bary has been one of the most extensively studied plant pathogens. It is now commonly perceived as a typical example of an aerial, almost obligate parasite, but the soil stages of its life cycle often have been overlooked. However, sexual or asexual soilborne inoculum is (or could be) significant in three major areas of the biology and pathology of P. infestans: (i) survival of the pathogen and production of primary inoculum (19,25,40); (ii) infection of daughter tubers (49,56); and (iii) variability and evolution of the pathogen (31).