Sexual Sporulation in the Basidiomycota
- Formation of basidiospores:
- 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:
- 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.
- 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.
- 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.