Pythium irregulare causes damping-off and root rot of
plants. P. irregulare has hundreds of plant hosts and
infects under moist conditions that favour the movement of
zoospores. Infections can occur under field and greenhouse
conditions.
The pathogen grows and colonizes a plant by producing hyphae. When
hyphae from opposite mating types meet, they fuse and produce
oospores, which serve as overwintering structures. Upon
germination, an oospore either forms hyphae or develop a
zoosporangium, which produces motile zoospores that swim and infect
plants. When reaching the root cortex, zoospores form cysts that
then germinate, infect and invade the plant root. The infection
progresses with the growth of hyphae. (Purdue Extension)
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