Pythium
Introduction
Pythium aphanidermatum and P. ultimum are the main types of pythium. Both types have a wide range of host plants.
P. aphanidermatum prefers warmer environments, and can cause severe damage in every crop phase, particularly if the plant is in a weakened condition.
P. ultimum is active at lower temperatures, and mainly affects seedlings.
Life cycle
Pythium primarily damages young, soft plant tissue. The infection enters through injuries in the root system. Thick-walled resting spores form in affected tissue. These resting spores can survive for over two months in soil or substrate. In favourable conditions, the resting spores germinate and ultimately form swarm spores (zoospores): these are motile spores with a flagellum. These swarm spores disperse themselves through water and splashing soil particles.
Indicators of damage
Light brown wet rot forms where the soil or substrate comes into contact with the air. Ultimately, the base of the plant can actually rot right through. The fungus can also damage the roots. The bark then becomes loose from the central root cylinder and slides off easily.
