6 Wood Discoloration

2.2 Growth and Spreading 19
Fig.2.12. Generalized life cycle of an euascomycete. A ascospores or conidia, B germinated
monokaryons, C plasmogamy of ascogonium (As)-trichogyne (T) and antheridium (An),
D–G section of ascogonium after incorporation of “male” nuclei, D ascogenous hypha, E
hook formation, F karyogamy in the tip hypha, G dikaryon and ascus after meiosis, H ascus
after mitosis with eight ascospores, I anamorph with conidia
the essential ascomycete with nutrition function and theoretically unlimited
growth. Conidia may develop at the haploid mycelium as anamorph (I).
Within the fruit body, hyphae develop to gametangia (“sexual organs”, C)
connectedwithmitosis.Thetrichogyne(T,“copulationhypha”),whichderives
from the ascogonium (As, “female gametangium”), fuses (plasmogamy, gametangiogamy)
with the antheridium (An, “male gametangium”). The nuclei
fromtheantheridiummigrate(therefore:male)throughthetrichogyneintothe
ascogonium. There may be various modifications of the generalized scheme:
Antheridia are absent, and mono-nuclear spermatia (from an anamorph) fuse
with the trichogyne (deuterogamy). Somatogamy of “normal” hyphae takes
place (see Chap. 2.2.3.2). One sex is missing or not functional, and fertilization
occurs between two nuclei of the same sex (automixis).
In the hymenial Ascomycetes (Ascohymeniales, wood-inhabiting Ascomycetes),
the fruit bodies (ascocarps, ascomata) develop after the fertilization of
the ascogonium from basal cells of the gametangia, and thus the fruit bodies
predominantly consist of haploid hyphae (Fig. 2.13).
From the “pollinated” ascogonium, ascogenous hyphae develop, into which
migrates each one pair of two genetically different (compatible) nuclei. In
Ascomycetes, the dikaryotic phase is limited and without nutrition function.
By means of hook formation (Fig. 2.12E) the short-lived hook mycelium and
the ascus (meiosporangium) develop, in which karyogamy and meiosis occur.
Before ascospore formation, there is commonly an additional mitosis, which
bringsthenumberofascospores(meiospores)intheascustoeight.Themature
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