In this article we will discuss about the ways of zygospore germination in lower fungi.
(a) The diploid contents of the zygospore (A) undergo meiosis but meiospores are not formed. The zygospore containing the haploid protoplast then directly germinates to give rise to new haplomycelium (B). Monoblepharis is an example.
Rarely as in Allomyces, the diploid zygospore (C) germinates by putting out a germ tube (D) which grows and branches to form the diplomycelium. No meiosis takes place prior to or during germination of the zygospore.
(b) Prior to germination, the diploid unclei undergo zygotic meiosis. The resultant haploid nuclei are fashioned into meiospores. The latter are extruded either by the rupture of zygospore wall into a sessile vesicle (E, Albugo Candida) or the zygospore forms a short exit tube which terminates in a vesicle (F, Pythium perioplocum).
With the bursting of the vesicle wall, the meiospores are liberated. They swim about for a while, retract their flagella and encyst. The encysted meiospore germinates by a germ tube.
(c) In some other species, the diploid contents of the zygospore, prior to germination, undergo meiosis. Upon germination, the haploid contents grow into a hypha which grows to a limited extent. It is called the promycelium. The latter bears a terminal sporangium or germ sporangium.
The haploid contents of the germ sporangium undergo cleavage to form either motile (Plasmopara viticola, G), or non-motile (Mucor, H) germ spores. The former are called meiozoospores and the latter meioaplanospores. On liberation, each germ spore germinates under suitable conditions to form the haplomycehum.
