Release of Zoospores by Pythium


Pythium is a fungus-like organism. One of
the facts that separates it from true fungi is the fact that it forms a swimming spore
form called a zoospore, and true fungi don’t do that. Now, what you’re going to see is
in the lower part of the picture, the hyphae, and on the end of the hyphae is kind of a
lemon shaped structure called the sporangium, and when the temperature and moisture conditions
favor, what happens is the cytoplasm and the sporangium begins to form the zoospores and
in the case of pythium, the sporangium forms a vesicle, or sort of like a balloon like
structure at the end of the sporangium. But the cytoplasm moves from the sporangium into
the vesicle and then starts dividing up to zoospores. You can sit and watch, with a compound
microscope as that happens. Over about a five-minute period, the zoospores begin to form and then
they become very active. And that’s what we’re going to see in the video. Over time they
start moving a little bit faster and a little bit faster. Then eventually, the vesicle breaks
and the zoospores are released. What you’ll see towards the very end of this video is
that one of the zoospores gets trapped in the vesicle, and you will be able to see one
of the vesicles in the lower left hand area. It looks like a line or kind of a little faint
shadowy area, but eventually that zoospore is released. The end result is hyphae gives
rise to one sporangium, but that one sporangium gives rise to many many zoospores, and theoretically,
each zoospore could infect a different root. So the end result would be you can get a lot
of infection from a very little bit of pithium. The difference between pythium and phytophthora
is phytophthora releases the zoospores directly from the sporangium and it doesn’t form a
vesicle outside the sporangium.

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