Sexual Sporulation in the Basidiomycota

Formation of basidiospores:
Diagram illustrating basidiospore formation.
  • Two HAPLOID NUCLEI in an apical dikaryotic hyphal compartment (often within a basidiocarp) FUSE to form a DIPLOID NUCLEUS.
  • The DIPLOID NUCLEUS undergoes MEIOSIS to yield four haploid nuclei.
  • Four small outgrowths - STERIGMATA - begin to form at the top of the hyphal compartment and the tip of each sterigma begins to inflate.
  • A fluid-filled VACUOLE develops near the base of the compartment and gradually enlarges - as it enlarges it forces protoplasm into the inflated portions of the sterigmata.
  • When each swelling at the tip of a sterigma has almost attained its full size a NUCLEUS PASSES INTO IT.
  • The uninucleate swelling at the the tip of each sterigma matures into a BASIDIOSPORE.
  • The compartment supporting the sterigmata and basidiospores is called a BASIDIUM.
Classification of fungi belonging to the Basidiomycota is based upon the presence or absence of fruiting bodies (BASIDIOCARPS) and the type of basidiocarp formed.
Basidiocarps are amongst the most familiar of fungal structures, including toadstools, brackets and puff-balls. But the Basidiomycota also contains many species that produce microscopic sporulating structures, i.e. micro-fungi.
Classification of fungi belonging to the Basidiomycota:

1. Teliomycetes

  • In this group the basidia are NOT grouped together side-by-side in or on a basidiocarp (fruiting body).
  • The UREDINALES and USTILAGINALES are two important orders of PLANT-PATHOGENIC FUNGI belonging to the Teliomycetes.

2. Hymenomycetes

Diagram illustrating fruiting bodies in the Hymenomycetes.
  • The largest class in the Basidiomycota.
  • The basidia are arranged in a layer known as a HYMENIUM that is fully exposed at maturity.
  • The hymenium may cover the surface of GILLS, line VERTICAL DOWNWARD-FACING PORES, or cover an ERECT CLUB or SYSTEM OF VERTICAL BRANCHES or TEETH.
Example of a basidiocarp in the Hymenomycetes. - CLICK TO VIEW THIS EXAMPLE OF A BASIDIOCARP FROM THE HYMENOMYCETES - 100 KB

3. Gasteromycetes

  • Includes fungi known as PUFF-BALLS, EARTH-STARS and BIRDS' NEST FUNGI.
  • The spore-producing hymenium is NOT EXPOSED at maturity.
  • But these fungi have evolved a variety of mechanisms to ensure efficient spore liberation.

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