Chapter 8 Biological Classification Part 2 by Teaching Care online coaching classes

(10)  Salient features of classes

• Phycomycetes (Oomycetes/Egg  fungi)  : It is also called lower fungi, mycelium is coenocytic. Hyphal wall may contain chitin or cellulose (g., Phytophthora). Asexual reproduction occurs with the help of conidio- sporangia. Under wet conditions they produce zoospores. Under dry conditions, the sporangia directly function as conidia. Zoospores have heterokont flagellation (one smooth, other tinsel). Sexual reproduction is oogamous. It occurs by gametangial contact where male nucleus enters the oogonium through a conjugation tube. The fertilized oogonium forms oospore. e.g., Sapolegnia, Albugo (Cystopus), Phytophthora, Phythium, Sclerospora.
• Zygomycetes (Conjugation fungi) : Mycelium is coenocytic. Hyphal wall contains chitin or fungal cellulose. Motile  stage  is  absent.  Spores  (Sporangiospores/aplanospores)  are  born  inside  sporangia.  Sexual reproduction involve fusion of coenogametes through conjugation (Gametangial copulation). It produces a resting diploid Zygospore. On germination, each zygospore forms a germ sporangium at the tip of a hypha called promycelium g., Mucor, Rhizopus.
• Ascomycetes (Ascus : sac, mycete : fungus) : These are unicellular as well as multicellular In the latter, mycelium is septate. The asexual spores formed in chains are called conidia. The spores are formed exogenously, i.e. outside sporangium. They detach from the parent and form new mycelia. Sexual reproduction is through ascospores, which are formed endogenously (within the mycelium) in a sac like structure called ascus (pl. asci). The gametes involved in sexual reproduction are nonmotile compatible and are generally represented as + and –. The fusion of gametes is followed by reductional division that produces haploid ascospores. The fruiting body called ascocarp.

The ascocarp are of four types :

• Cleistothecium : It is an ovoid or spherical fruiting body which remains completely closed g., Aspergillus.
• Perithecium : It is a flask shaped fruiting body which opens by a single pore called ostiole. It is lined by sterile hyphae called paraphyses. The asci are also mixed with paraphysis g., Cleviceps.
• Apothecium : It is a saucer-shaped fruiting The asci constitute the fertile zone called hymenium

e.g., Peziza.

• Ascostroma : It is not a distinct fruiting body. It lacks its own well defined wall. The asci arise directly with a cavity (locule) of It is also called as pseudothecium e.g., Mycosphaerella.
• Basidiomycetes : They are the most advanced fungi and best decomposers of These are called club fungi because of a club shaped end of mycelium known as basidium. They have septate multinucleated mycelium. Septa possess central dolipores and Lateral clamp connections. The sexual spores called basidiospores are generally four in number. They are produced outside the body (exogenuous) unlike ascomycetes where they are endogenous. Two compatible nuclei fuse to form zygote, which undergoes meiosis and forms four basidiospores. The fruiting body containing basidia is a multicelular structure called basidiocarp. The common members are edible mushrooms (Agaricus). Smut and Rust.
• Deuteromycetes (Fungi inperfecti) : The group include all those fungi in which sexual or perfect stage is not known. Mycelium is made of septate Asexual reproduction commonly occur by means of conidia.

(11)  Economic importance

• Harmful aspects
• Crop diseases : Several important crop plants are destroyed due to fungi diseases. Some important ones are listed here under :

Some plant disease caused by fungi

• Diseases in human beings : Several diseases in human beings are found to be caused by fungi infecting different parts of the Some of them are given hereunder as :

• Spoilage of food : Some forms like Rhizopus, Mucor, Aspergillus, Cladosporium grow on food articles and spoil Cladosporium grows even at a temperature of – 6°C.
• Mycotoxins : Some fungi produce toxic metabolites which cause diseases in human They usually contaiminate cereals and oil seed crops. Four types of mycotoxins are generally identified :
  • Aflotoxins : g., Aflotoxin B₁, B₂, M₁, M₂, G₁, G₂; They are produced mainly by Aspergillus flavus and A. parasiticus. They are well know for their carcinogenic effect.
  • Zearalenone : It is produced by Fusarium
  • Ochratoxins : They are produced by Aspergillus and Pennicillium
  • Trichothecenes : They are produced by fungi like Cephalosporium, Fusarium
• Poisonous fungi : Some fungi are extremely poisonous g., Amanita phalloides (‘death cup’). A. verna, Boletus satanus. Forms like Coprinus, Psilocybe are less poisonous. The fungus Amanita phalloides produces toxins like a-amanitin, phalloidin etc. which are very poisonous.
• Ergotism :The fungus causing ‘ergot’ disease of rye (Secale) is Cleviceps purpurea. It contains many poisonous alkaloids in their sclerotia. It causes poisoning in human beings. It’s acute condition is called as ‘ Anthony’s fire‘.
• Hallucinogenic drugs : The hallucinogenic drug LSD (Lysergic acid Diethylamide) is extracted from

Cleviceps purpurea as also from Inocybe. Besides, the mushroom Amanita muscaria is also hellucinogenic.

• Rotting of wood : Rotting of wood is caused due to degradation of lignin and cellulose. It is brought about fungi like Polyporus , Fomes sp. and Ganoderma sp., Forms like Fusarium, Penicillium leave stains on the wood.
• Allergies : Spores of Mucor, Aspergillus, Penicillium, Puccinia , present in the atmosphere cause allergies.
• Deterioration of articles : Forms like Aspergillus, Cladosporium, Rhizopus, Chaetomium, Alternaria

deteriorate cork, rubber, leather, textile and even plastics.

(ii)  Useful aspects

• Food : Forms like Agaricus bisporus, Morchella esculenta, Lentinus edodes, Clavatia gigantia, Volvariella volvacea are The yeast Saccharomyces cerevisiae is used for making ‘yeast cake‘. When mixed with cereal flour, the yeasts produce a preparation called incaparina. The Single Cell Protein (SCP) obtained from yeasts, Penicillium, Fusarium etc. are used as substitute of protein food, Rhizopus oligosporus, when processed with soybeans yield a food preparation called ‘tempeh’. It has high protein contents.
• Flavoring of food : Penicillium roquefortii and camemberti are employed for flavoring cheese.
• Brewing and baking : Yeasts are generally used in bakeries and breweries. The sugars are fermented by yeasts into alcohol and CO₂. While the former in main product of breweries CO₂ is mainly useful in
• Organic acids : Several organic acids are commercially produced by fungi, some of which are given hereunder :

• Antibiotics : The antibiotics are chemicals produced by living organisms that kill other living The first known antibiotic is penicillin that was extracted from Penicillium notatum by A. Fleming, (1944). Raper (1952) also extracted the same antibiotic from P. chrysogenum. Besides, several other antibiotics have been extracted since then.

• Other chemicals : Various chemicals have been obtained from different kinds of Yeast are good source of glycerol and enzymes like zymase, invertase and lipase. Cellulases are obtained from Aspergillus. Some alkaloids are also obtained from fungi e.g., Ergotinine, Ergotetrine and Ergobasine from Cleviceps purpurea. Gibberellins (plant hormones) are obtained from Gibberella fujikuroi. Another hormone, trisporic acid is obtained from Mucor mucedo.
• Biological assays : The fungi can detect the presence of certain chemicals present in the medium even in traces g., Aspergillus niger for Mn, Pb, Zn, Cu, Mo etc.
• Vitamins : Various vitamins have been obtained from different kind of

(i)  Other uses

• Nitrogen fixation by yeasts like Saccharomyces and Rhodotorula.
• Production of latex by Mycena galopus.
• Soil building by Rhizopus, Cladosporium, Aspergillus
• Along with bacteria, the fungi work as
• Biological control of growth of hyperparasites like insects, nematodes, bacteria and even other
• Neurospora is a good research material for geneticists and Physarum for molecular biologists for the study of

Important Tips

• Fungus : The term was used by Gaspard Bauhin (1560–1624).
• Father of Mycology : Pier Antonio In 1729 he wrote ‘Nova Genera Plantarum’ in which 900 fungi were described.
• Father of Systematic Mycology : M. Fries (1794–1878). He wrote ‘Systema Mycologicum’ in three volume.
• Father of Modern Mycology and Plant Pathology : A. de Bary.
• Father of Indian Mycology and Plant Pathology: J. Butler.
• Smallest Fungus : Yeast with a size of 3–15 mm × 2–10 m
• Largest Fungus : Lignocolous Shelf Fungus/Bracket Fungus Ganoderma applanatum (fruiting body 60 cm across). Glant Puffball/Clavatia is 90–120 cm across. It possesses anticancer properties.
• Millardet discovered fungicide Bordeaux Which is solution of copper sulphate and calcium hydroxide (CaSO₄ + Ca(OH)₂).
• Pseudogamy : Fusion between unrelated
• Pedogamy : Fusion between mature and immature
• Adelphogamy : Fusion between mother and daughter cells or sister cells.
• Non-ciliated spores called ‘aplanospores’.

Bipolar heterothallism found in Mucor and Rhizopous. Reserve food material of fungi is glycogen and oil bodies.

A fungus which requires only one single host for complition of its life cycle is called ‘autoecious’. Phycomycetes are called algal fungi or lower fungi.

Fungi inhabiting wood are known as epixylic.

Aspergillus secretes toxin during storage conditions of crop plants. The hyphae of this fungus are septate and uninucleate. Ascomycetes are our worst fungus enemies.

Neurospora (an ascomycete) is known as Drosophila of plant kingdom. Peziza and Helvella are coprophilous fungi (grow on dung).

In higher Ascomycota the ascus develops indirectly from the tip of a bi-nucleate ascogenous hypha by becoming curved forming a

crozier.

Emperor Claudius Caesar was murdered by his wife by giving extract of toad stool fungus – Amanita phylloides which stops m-RNA synthesis, therefore it is called ‘Caesar’s Mushroom’.

About 2300 antibiotics have been discovered so far from various fungi. Of these, some 123 have been extracted from Penicillium and 115 from Aspergillus.

Destruction of potato crop by Phytophthora infestans in Ireland in 1845–49.

Decrease in the yield of coffee in Srilanka from 42 m. kg. to 3 m. kg due to Hemileia vastatrix. Destruction of 5 million elm trees in England in 1967–77 by Ceratocystis ulmi.

Destruction of 50% maize plants in USA (1970) due to infection of Helminthosporium maydis.

Famous famine of Bengal in 1942–43 was due to destruction of rice crop by Helminthosporium oryzae. Few leading Indian mycologists are : C.V. Subramaniam, T.S. Sadasivan, K.C. Mehta and B.B. Mundkar. The fungi which grow on tree are called as lignicolous fungi e.g. Polyporus.

Keratimorphic fungi appear on nails, feathers, hairs, hoofs etc. Hydnum from order agaricales is called tooth fungus.

Balanced Parasites : Parasites which draw nourishment from hosts without killing or weakening them are called balanced parasites. The parasites which bring about disease and destruction of the hosts are known as destructive parasites.

Biotrophic Parasite (Gaumann, 1946). Absorbs nutrients from living host/cells.

Nacrotrophic Parasite (Gaumann, 1946). Kills host cells for obtaining nourishment.

Luminescent Fungi. They make wood/leaves/soil luminescent at night. Luminescent parts are pileus in Panus and Pleurorus species, fruiting body and mycelium in Clitocybe illudens.

Acetyl Glucosamine/Chitin. (C₂₂H₅₄N₄O₂₁)n.

Vegetative Vultures. Saprophytic fungi have been called vegetative vultures by Rolfe and Rolfe (1926) as they function as natural scavengers.

Primary Host. Host in which the parasite becomes sexually mature. In stem rust the primary host is Wheat (karyogamy occurs) while alternate/secondary host is Barberry.

Penicillin – Penicillium chrysogenum (initially from P. notatum) first antibiotic drug called wonder drug (discovered by Fleming, 1929).

Species of Morchella are commonly known as ‘morels’, ‘sponge mushrooms’ or ‘gucchi’. The species of Polyporus are commonly called ‘bracket fungi’ or ‘self fungi’.

Phytotoxin are secreted by plants in response to fungal reactions. They are generally phenolic compound. Coprophilou fungi grow on dung e.g., Pilobolus crystallinus.

Fungi can be stained by cotton blue.

Deuteromycetes is also known as ‘Fungal waste Basket’. The edible part of mushroom is basidiocarp.