Introduction to Fungi, Third Edition

CONIDIUM PRODUCTION IN ASCOMYCETES
233
Fig 8.7 Enteroblastic phialidic (left) and enteroblastic (right) annellidic conidiogenesis. From de Hoog et al.(2000a),withkind
permission of Centraalbureau voor Schimmelcultures.
Phialidic conidiogenesis
Annellidic conidiogenesis
a. Apex of conidiophore expands to form a phialide a. Apex of conidiophore differentiates to form a conidiogenous
with a blown-out holoblastic conidium initial (o).
cell (annellide) and the initial of a holoblastic first conidium (1).
b. The first-formed conidium (1), surrounded by a new wall b. The first conidium is cut off by a septum.
secreted inside the phialide, is pushed out and breaks
the outer wall of the phialide whose tip persists as a cap.
c. The first conidium is cut off by a septum. c. A second conidium (2) develops beneath the first.
d. A second conidium develops below the first, also d. The septum cutting off the second conidium is formed beyond
surrounded by new wall secreted inside the phialide. the point at which the original annellide wall was ruptured
and persists as an annellation.
e. A third conidium develops in basipetal succession
adding to the length of the conidial chain.The lower
part of the broken original wall of the phialide has
persisted as a collarette, the extent of which is shown
by vertical dashed lines. Successive layers of wall
material may accrete in the neck of the phialide to
form a periclinal thickening.
e. The development of further conidia results in the addition
of more annellations so that an annellated zone, marked by
vertical dashed lines, increases in length.
thickening may be seen even with the light
microscope, but in others it is less obvious.
During maturation of the phialoconidium,
the spore may increase in size, its wall may
become thickened and ornamented by spines
and may become pigmented by melanin and
other materials. In some genera of ascomycetes
and their conidial derivatives, the phialospores
are dry and appear in chains. Dry-spored conidial
chains are often persistent and are typical of
Aspergillus and Penicillium (see Figs. 11.16 11.18).
The hydrophobic nature of the spore wall is due
to incorporation of hydrophobin rodlets. The
adherence of the conidia in chains depends on
the strength of the septum between adjacent
spores. Secession of the conidia into separate
spores occurs by breakage of the septum. Where
the spore wall is wet, the succession of conidia
may briefly persist in the form of a short chain
(false chain) or may collapse into slimy balls at
the tips of the phialides (no-chain phialides).
An example of the latter is Trichoderma (conidial