Edited by Ho Dinh Hai Long An - Vietnam Updated: 08/05/2014
1- Introduction to Fungi
Common Edible Mushrooms
1.1- Definition of Fungus The Biology Online Dictionnay define fungus as bellow: Fungus (Science: microbiology) A generalterm used to denote a group of eukaryoticprotists, including mushrooms, yeasts, rusts, moulds, smuts, etc., which are characterised by the absence of chlorophyll and by the presence of a rigid cell wall composed ofchitin, mannans and sometimes cellulose. They are usually of simplemorphologicalform or show some reversiblecellularspecialisation, such as the formation of pseudoparenchymatous tissue in thefruiting body of a mushroom. The dimorphicfungigrow, according to environmental conditions, as moulds or yeasts. Source: http://www.biology-online.org/dictionary/Fungus 1.2- Etymology The English word fungusis directly adopted from the Latinfungus (mushroom), used in the writings of Horace and Pliny. This in turn is derived from the Greek word sphongos("sponge"), which refers to the macroscopic structures and morphology of mushrooms and molds; the root is also used in other languages, such as the German Schwamm ("sponge") and Schimmel ("mold"). The use of the word mycology, which is derived from the Greek mykes (mushroom) and logos (discourse), to denote the scientific study of fungi is thought to have originated in 1836 with English naturalist Miles Joseph Berkeley's publication The English Flora of Sir James Edward Smith, Vol. 5. 1.3- Classification of Fungi + General A fungus (plural: fungi or funguses) is any member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds (British English: moulds), as well as the more familiar mushrooms. This fungal group is distinct from the structurally similar myxomycetes (slime molds) and oomycetes (water molds). The discipline of biology devoted to the study of fungi is known as mycology (from the Greek μύκης, mukēs, meaning "fungus"). Mycology has often been regarded as a branch of botany, even though it is a separate kingdom in biological taxonomy. Genetic studies have shown that fungi are more closely related to animals than to plants. Living things are organized for study into large, basic groups called kingdoms. Fungi were listed in the Plant Kingdom for many years. Then scientists learned that fungi show a closer relation to animals, but are unique and separate life forms. Now, Fungi are placed in their own Kingdom, Fungi, which is separate from plants, animals, protists, and bacteria. These and other differences show that the fungi form a single group of related organisms, named the Eumycota (true fungi or Eumycetes), that share a common ancestor (is a monophyletic group). Because of these, fungi are now not plants! + Classification of fungi The Fungus Kingdom encompasses an enormous diversity of taxa with varied ecologies, life cycle strategies, and morphologies ranging from unicellular aquatic chytrids to large mushrooms. However, little is known of the true biodiversity of Kingdom Fungi, which has been estimated at 1.5 million to 5 million species, with about 5% of these having been formally classified. The organisms in kingdom fungi include mushrooms, yeasts, molds, rusts, smuts, puffballs, truffles, morels, and molds. More than 70,000 species of fungi have been identified. Fungi are usually classified in four divisions: -The Ascomycota (yeasts and sac fungi). -The Basidiomycota (club fungi). -The Chytridiomycota (chytrids). -The Zygomycota(bread molds) Placement into a division is based on the way in which the fungus reproduces sexually. The shape and internal structure of the sporangia, which produce the spores, are the most useful character for identifying these various major groups. (1)- Division Ascomycota: Sac Fungi The sac-fungi produce spores in small cup-shaped sacs called asci, hence the name ascomycota. The mature sac fungi spores are known as ascospores, they are released at the tip of the ascus breaks open. Yeast is the most common one-celled fungi. Yeast reproduces through asexual process called budding. The buds form at the side of the parent cell, they pinch-off and grow into new yeast cell which is identical to the parent cell. The group of Ascomycetes include a wide variety of species, which are very different in size and living conditions. They are equipped with asci, sac-like structures that produce sexed spores (ascospores), which form at the end of the hyphae and are called conidia. This group includes yeast, edible mushrooms (Morchella esculenta and truffles) and some marine species. Examples: morels, truffles, cup fungi and powdery mildews (such as Aspergillus, Claviceps, Neurospora). (2)- Division Basidiomycota: Club Fungi Basidiomycota includes the mushrooms, puff-balls, smuts, rusts and toadstools. The spores are borne on a club-shaped spore case called basidium. In mushrooms the basidia are lined at the gills under the cap. Huge numbers of spores are produced by the club fungi. In fact, an average sized mushroom produces over 16 billion spores. These spores rarely germinate or mature. Group of Basidiomycetes includes edible mushrooms and plant parasites such as smuts and rusts. They usually consist of a fruit-bearing body composed of a stipe and cap, which forms when the fungus reproduces through sexed reproduction. The lower part of the cap is provided with a series of parallel or entwined lamellae, which host the basidia, tiny sporangia where sexed spores are formed. Nevertheless, the most frequent form of reproduction is the asexual one, which occurs through the spores produced by the conidia. Examples: Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus). (3)- Division Deuteromycota: Imperfect Fungi These organisms are known as imperfect fungi because they lack sexual reproduction. Group of Deuteromycetes includes the species in which no sexual reproduction cycle has ever been observed and that cannot be grouped under any one of the other three classes. They reproduce by asexual spores known as conidia. Most of the fungi causes diseases to humans like ringworm, athlete's foot. Examples: Economically important imperfect fungi are Penicillium and Aspergillus. Other examples are Alternaria, Colletotrichum and Trichoderma. (4)- Division Zygomycota: Zygote forming Fungi These fungi are usually found on cheese, bread, and other decaying food. They are zygote forming fungi, hence the name zygomycota. The spores are produced in round-shaped case called sporangium. The grayish fuzz seen on bread and decaying food is actually mass of mature sporangia mold. Under the microscope they are seen as pinheads. When the sporangium breaks open hundreds of spores are released. The group Zygomycetes are Fungi living in the soil or on decomposing animal or vegetal organic material. Their reproduction is asexual and occurs by scattering spores, which are produced in special structures (black bulb-type sporangia). If the spores are formed in a different type of sporangium (zygosporangium), a sexed cycle occurs. This group includes the “black mildew” which develops on fruits, vegetables and many baked products. Many species in the class Zygomycetes form mycorrhizas. Examples: Mucor, Rhizopus (the bread mould) and Albugo. Note! There are also two conventional groups which are not recognized as formal taxonomic groups (ie. they are polyphyletic); these are the Deuteromycota (fungi imperfecti), and the lichens. The Deuteromycota includes all fungi which have lost the ability to reproduce sexually. As a result, it is not known for certain into which group they should be placed, and thus the Deuteromycota becomes a convenient place to dump them until someone gets around to working out their biology. Unlike other fungi, the lichens are not a single organism, but rather a symbiotic association between a fungus and an alga. The fungal member of the lichen is usually an ascomycete or basidiomycete, and the alga is usually a cyanobacterium or a chlorophyte (green alga). Often the fungal partner is unable to grow without the algal symbiont, making it difficult to classify these organisms. They will be treated here as a separate group, but it should be realized that they are neither single organisms, nor a monophyletic group. It should also be noted that some organisms carry the name of mold or fungus, but are NOT classified in the Kingdom Fungi. These include the slime molds and water molds (Oomycota). The slime molds are now known to be a mixture of three or four unrelated groups, and the oomycetes are now classified in the Chromista, with the diatoms and brown algae.