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A specific feature of the sexual reproduction of Ascomycetes and Basid-iomycetes is that plasmogamy of haploid cells and karyogamy of two nuclei (n) to form a diploid nucleus (2n) are separated from each other temporally as well spatially by the dikaryophase (two-nuclei phase, dikaryon, n + n, ===)




(Fig.1). A dikaryotic hypha is one with two nuclei that derive from two haploid hyphae, but in which the nuclei are not yet fused by karyogamy. Particularly in Basidiomycetes, the dikaryotic phase is considerably ex-tended. By conjugated division of the two nuclei (conjugated mitosis), by division of the dikaryotic hypha, and by means of a special nucleus migration connested with camp formation both daughter cells become again dikaryotic.



 Ascomycetes 


The life cycle of a typical ascomycete is shown in Fig.1 (also Muller and Loeffler 1992; Eaton and Hale 1993; Schwantes 1996; Jennings and Lysek 1999). Haploid (n) spores (A, ascospores or conidia from an anamorph) germi-nate to haploid hyphae and after mitoses to haploid mycelium (B), which is the essential ascomycete with nutrition function and theoretically unlimited growth. Conidia may develop at the haploid mycelium as anamorph .



Fig.1  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 







 Within the fruit body, hyphae develop to gametangia ("sexual organs", C) connected with mitosis. The trichogyne (T, "copulation hypha"), which derives from the ascogonium (As, "female gametangium"), fuses (plasmogamy, gametangiogamy) with the antheridium (An, "male gametangium").



The nuclei from the antheridium migrate (therefore: male) through the trichogyne into the 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.




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 Ascomy-cetes), 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.)



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. ) the short-lived hook mycelium and 1(meiosporangium ) develop, in which karyog,ar. and, meiosis occur. Before ascospore formation, there is commonly an additional mitosis, which brings the number of ascospores (meiospores) in the ascus to eigth.


Fig. 2 Structure of a fruit body (apothecium) of an ascomycete predominantly consisting of haploid hyphae (thin lines, one nucleus), some dikaryotic hyphae (thick lines, two nuclei) and differently matured asci within the hymenium. As-, An ascogonium and antheridium before gametangiogamy, As+ fertilized ascogonium 




 The mature ascus is usually tube-shaped ("tube fungi"). The non-flagellate ascospores disper after disintegration of the ascus or via different opening mechanisms. The ascospores are mono-nuclear or after further mitosis multi-nuclear. They can be septate and show similar conidia characteristics of size, shape, color and wall sculpturing. The relatively small fruit bodies (less than 1 mm in diameter) of the wood-inhabiting Ascohymeniales are the spherically closed cleistothecium, the pearshaped perithecium, e.g., in several blue-stain fungi, or the disk-shaped apothecium .



Fig. 3 Fruit body types of Ascomycetes. P perithecium, A apothecium, C cleistothecium 









Basidiomycetes








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