Introduction to Fungi, Third Edition

198 ZYGOMYCOTA
Fig 7.30 Mortierella hyalina. (a) Branched sporangiophore as viewed with the dissection microscope. (b) Intercalary chlamydospore.
(c) One-spored sporangium (sporangiolum) showing separate walls, the outer belonging to the sporangium and the inner to the
sporangiospore. (d) Multi-spored sporangium with the sporangial wall disintegrating. (e) Apex of a sporangiophore in which the
sporangium has dehisced, leaving fragments of the sporangial wall as a frill. Note the absence of a bulging columella. (b e) to same
scale. Reprinted from Weber and Tribe (2003), with permission from Elsevier.
Zygospore production takes place in culture,
often embedded in the agar, on media with a
relatively poor nutrient content which
discourages profuse development of aerial mycelium.
A common feature is that zygospores are
heterogametangic, one suspensor being considerably
larger than the other. The smaller progametangium
or gametangium does not enlarge
and may disappear soon after plasmogamy. The
early development of such heterogametangic
zygospores is illustrated in the heterothallic
M. umbellata (Fig. 7.32; Degawa & Tokumasu,
1998). In this species, hyphal coiling occurs at the
point of contact of compatible mycelia, followed
by the development of club-shaped progametangia
which grow parallel and closely appressed to
each other. One, the macroprogametangium,
soon becomes much larger than the other, the
microprogametangium. In each progametangium
a septum delimits a terminal gametangium
from a suspensor. The macrogametangium
and macrosuspensor both enlarge considerably,