Basidiomycota (Basidiomycetes or Club – Fungi)
These are among the most familiar fungi: edible mushrooms, devastating plant pathogens rusts and smuts, puffballs, and bracket/shelf fungi are all club fungi. Basidiomycetes are named so for their characteristics, club-shaped (hence also called club fungi) sexual reproductive structure, the basidium (plural basidia). Nuclear fusion in the basidium is followed by meiosis.
Fig. 8.10Basidiomycetes. A meshroom’s fruiting structures. The gills on underside of mushroom’s cap are lined with basidia, on which basidiospores are produced.
Four haploid sexual spores, called the basidiospores, are born on, not inside, each basidium. During most part of their life cycle the hyphae are septate; the cells are uni-nucleate during one phase, and binucleate (dikaryotic) during the remaining, lengthy phase. Their characteristic fruiting bodies, or visible mushrooms, are formed entirely of dikaryotic mycelium. Puccinia species are most common rust fungi, and Ustilago species most common smut fungi.
| Rusts are called so because of numerous rusty, orange-yellow coloured disease spots on their host surface (mostly stem, leaves), later revealing brick/rust-red spores of the fungus. Smuts are called so because of their black, dusty spore masses that resemble soot or smut; these spore masses replace the grain kernels such as those of wheat, corn etc. (Fig. 8.22, 8.15) |
Spores (teliospores) of Ustilago tritici (loose smut of wheat) are carried by wind from infected wheat ears to healthy flowers, where they germinate, the resulting hyphae penetrate flower ovaries. Inside the ovary mycelium spreads and becomes dormant and remains so in the seed (grain). When such infected seeds are sown next season, the hyphae also grow within the growing plant and form smut spores inside the kernel, thus destroying them completely. The covering of the grain braks exposing the black spores mass, that may be dispersed by wind (fig. 8.11)
Fig. 8.11:disease cycle of loose smut of wheat caused by a club- fungus (ustilago tritici)
Deuteromycota (Deuteromycetes or Imperfect Fungi)
This heterogenous grou includes all such fungi in which sexual phase has not been observed. Most of them are related to their sexually reproducing relatives of ascomycetes; however some are related to other two phyla (Zygomycota, Basidiomycota) as well. If sexual structures are found on an imperfect fungus, it is then reassigned to the appropriate phylum. Biologists now can classify most imperfect fungi on the basis of DNA sequences, though sexual structures may not be found.
| Despite absence of sexual reproduction, imperfect fungi show special kind of genetic recombination, called parasexuality, in which portions of chromosomes of two nuclei lying in the same hypha are exchanged. |
Penicillium (blue, green molds), Aspergillus (brown molds), Alternaria, fusarium, helminthosporium are some of the economically important genera of Deuteromycetes (see economic importance of fungi).
Penicillium sp. (blue, green molds) are wide spread saprotrophic species common on decaying fruit, bread etc. its hyphae are septate. Penicillium reproduces asexually by means of naked spores called conidia. These are found in chains at the tips of special hyphae called conidiophores, which are branched. Brush-like arrangement of its conidia is characteristic of penicillium (fig. 8.12). these conidia give colour to the mycelia colony, which is circular. Mature conidia are easily and readily dispersed.
Fig. 8.12penicillium (a) a moldy orage: the blue mold is caused by saprobic species of penicillium. (b) penicillium showing asexual reproduction, characteristic brush-like arrangement of conidia.