Fungi and their Economic Importance

Study Notes

Fungi were originally classified with photosynthetic plants, but later separated and grouped with algae and protozoa (protista) and eventually placed in the Kingdom Mycota.
Fungi lack chlorophyll and have cell walls containing chitin, mannan, and β-glucans, characteristics shared with some animal cells.

Fungi are divided into two broad groups: microscopic (moulds and yeasts) and macroscopic (mushrooms, puffballs, jelly fungi, etc.).
Microscopic fungi can exist as unicellular (yeasts) or multicellular forms, while macroscopic fungi are primarily filamentous in growth form.
Fungal bodies consist of long, slender filaments called hyphae, which together form an entangled mass called mycelium.

Hyphae are of two types: aseptate (coenocytic) and septate.
Aseptate hyphae are continuous or branching filaments filled with cytoplasm and multiple nuclei.
Septate hyphae are made up of long chains of cells joined end-to-end and divided by cross-walls called septa, which have pores.

Vegetative hyphae grow as submerged or surface filaments, digesting, absorbing, and distributing nutrients to other parts for growth and development.
Aerial hyphae project above the surface in culture medium.
Reproductive/fertile hyphae produce asexual spores on the surface of the substrate.

Fungi acquire nutrients through parasitism, saprophytism, or symbiotic associations with other organisms.
Parasitism: obtaining nutrients from another living organism (e.g., Phytophthora sp. being parasitic on cocoa plants).
Saprophytism: absorbing nutrients from dead organic matter (e.g., Termitomyces sp. feeding on litter).
Symbiotic associations: exchanging nutrients with other organisms, especially roots of higher plants, to form structures called mycorrhizae (e.g., Boletus spp. and Glomus spp. associating with roots).

Fungi reproduce through three ways: sexual, asexual, and vegetative (budding, as seen in yeast).
Asexual reproduction involves forming conidia or asexual spores, while sexual reproduction involves forming sexual spores.

Both sexual and asexual reproduction occur in fungi.
During asexual life cycle, spores settle on a substrate, develop an outgrowth known as a germ tube, and then elongate into a hypha.
Through continued growth and branching, an extensive mycelium is produced.

The four major groups of fungi are: Chytridiomycota, Zygomycota, Ascomycota, and Basidiomycota.
Chytridiomycota: characterized by motile spores (zoospores), commonly called chytrids.
Zygomycota (coenocytic true fungi): characterized by production of non-motile spores, with coenocytic mycelial organization.
Ascomycota (sac fungi): characterized by sexually produced spores (ascospores) contained within a sac-like structure called the ascus.
Basidiomycota (club fungi): characterized by production of basidiospores in a structure called the basidium.

Recycling of nutrients/maintenance of soil fertility: fungi decompose dead organic material, releasing nutrients back into the ecosystem, enhancing soil fertility and promoting crop productivity.
Formation of symbiotic association with plant roots: some fungi are vitally important for plant growth and development through mycorrhizal associations with plant roots.
Food: fungi are consumed directly as food or used indirectly in food and beverage industry (e.g., mushrooms, cheeses, bread, and some soya bean products).
Medicines: fungi produce antibiotics widely used to control diseases in human and animal populations (e.g., Penicillium chrysogenum).
Biocontrol of soil-borne pathogens: some fungi are used to control pests and nematodes in soil.
Crop diseases: fungi cause the majority of known plant diseases, which can result in significant economic losses if not treated with antifungal agents.
Animal disease: fungi can parasitize domestic animals, causing diseases, although this is not usually a major economic problem.
Spoilage of food and goods: fungi cause spoilage of food and other consumable goods, as well as rotting of wood.