How infection occurs Root and crown rot fungi live in the soil as saprophytes on dead plant material or survive by producing resistant resting structures. When new susceptible plants are transplanted into soil, the fungi grow into succulent roots and stems. Fusarium lives on dead plant tissue and in soil, and overwinters as thick-walled, resistant spores called chlamydospores. Cylindrocladium survives on dead plant material and as resistant resting structures called microsclerotia in the soil. Pythium and Phytophthora are blown with infested soil or splashed by rain or irrigation water.
Pythium survives by producing resistant structures called oospores in dead roots.
Immature, succulent roots and stems are most susceptible to significant plant damage when infected by Pythium . Well-developed woody plant seedlings have thicker, lignified cells that limit the spread of Pythium , so only the feeder roots are rotted. Fine feeder roots are vulnerable to damage at any stage of plant growth, but a plant with good vitality can limit the extent of Pythium growth into older roots. Phytophthora overwinters as oospores or chlamydospores in infected roots or stems. These are blown or splashed onto nearby susceptible plants which become infected.