Introduction to Fungi, Third Edition

140 CHYTRIDIOMYCOTA
Fig 6.9 Synchytrium mercurialis.
(a) Section of stem of Mercurialis
perennis showing hypertrophied cells
surrounding a resting sporangium.
(b) Germination of a resting
sporangium to release a sorus of
zoosporangia.Thus in S. mercurialis
the resting sporangium functions as
a prosorus (after Fischer,1892).
Fig 6.10 Pine pollen grains
colonized by Rhizophydium sp.
(a) The rhizoid system attaching
the epibiotic sporangium to the
colonized pollen grain. (b) Mature
sporangium; the cytoplasm has
become cleaved into numerous
zoospores.
found in crude cultures on pine pollen. The
zoospores are at first released into a hyaline
vesicle which soon dissolves, allowing them to
swim away. Gauriloff and Fuller (1987) have
outlined techniques for growing R. sphaerocarpon
in pure culture. This species can also grow
parasitically on filaments of the green alga
Spirogyra.
Douglas Lake (Michigan, USA) is surrounded
by conifers shedding pollen which floats on
the lake and becomes colonized by Rhizophydium
spp. Using the MPN (most probable number)
technique, Ulken and Sparrow (1968) have
estimated that the number of chytrid propagules
in the surface waters (epilimnion) can rise to
over 900 l 1 by late June. Some infected pollen
grains sink through the hypolimnion to the mud
at the floor of the lake. It is thought likely that
these develop resting sporangia which survive
the winter and provide inoculum to start off
colonization of new pollen deposits in the
following season.
Rhizophydium planktonicum
This species is the best-studied chytrid phytoplankton
parasite. It is a biotrophic pathogen of