Infection of tomato roots by P. lycopersici. (A) Light micrograph of a pycnidium with erupting conidia. (B) Light micrograph of conidiophores with conidia. (C) Stereomicrograph of a P. lycopersici microsclerotium germinating on artificial media. (D) P. lycopersici hyphae (black arrows) transformed with GUS + growing within young tomato roots. (E) Symptoms caused by P. lycopersici growing on young tomato rootlets artificially infected with the fungus. (F) Naturally-infected tomato roots with extensive corky root rot symptoms.