Classification of Fungi 

The classification of fungi is designed mainly for practical application but it also bears some
relation to phylogenetic considerations.
❖ The division of mycota, or fungi and moulds, includes the true slime moulds (Myxomycetes), the
lower fungi (Phycomycetes), and the higher fungi (Eumycetes).
❖ The fungi can be classified according to the various parameters including;
o Classification based on taxonomy hierarchy
o Classification based on spore Production
o Classification of medically important fungi
o Classification based on route of acquisition
o Classification based on virulence

Classification based on taxonomy hierarchy:

• Alexopolous and Mims proposed fungal classification in 1979. They place the fungi including the
• slime molds in the kingdom mycetae of the super kingdom Eukaryota which, in addition,
• includes four other kingdoms. They divide the kingdom mycetae into three divisions namely:
• Gymnomycota
• Mastigomycota
• Amastigomycota
• The division is subdivided into subdivision, classes, sub-classes, and orders.

Division I: Gymnomycota:

It includes phagotrophic organism devoid of cell walls. This
division comprises two subdivisions; Acrasiogymnomycotina and Plasmodiogynomycotina.

• Subdivision : Acrasiogymnomycotina: It includes a single class Acrasiomycetes.
  Class 1. Acrasiomycetes : Lacks flagellated cells except for one species. The class comprises:
  Sub class 1. Acrasiomycetidae
  Sub class 2. Dictyosteliomycetidae
• Subdivision: Plasmodiogymnomycotina: It is divided into two classes:
  Class 1. Protosteliomycetes
  Class 2. Mycomycetes: It includes the true slime mold and comprises three sub class namely:
  Sub class 1. Ceratiomyxomycomycetidae, 1 Order : Ceratiomyxales
  Sub class 2. Mycogasteomycetidae, 4 Orders: Liceales, Echinosteleales, Trichlales, Physarales
  Sub class 3. Stemonitomycetidae, 1 Order: Stemonitales
  

Division II: Mastigomycota:

• Includes fungi with absorptive nutrition, unicellular or
  filamentous, mycelium coenocytic. It comprises two sub divisions:
• Sub division: Haplomastigomycotina: Includes fungi with uni-or, bi-flagellate zoospores.
  Class 1. Chytridiomycetes– Fungi producing zoospores furnished with a single whiplash
  flagellum inserted at the posterior end.
  Class 2. Hyphochytridiomycetes- Motile cells with a single tinsel flagellum inserted at the
  anterior end.
  Class 3. Plasmodiophoromycetes- Parasitic fungi producing biflagellate motile cells with
  both the flagella of whiplash type inserted at the anterior end.
• Sub division: Diplomastigomycotima: Sexual reproduction ooagamous, zoospores
  biflagellate.
  Class 1. Oomycetes, 4 Orders: Lagenidiales, Saprolegnailes, Leptomitales, Peronosporales

Division III: Amastigomycota:

Fungi with absorptive nutrition, motile cells lacking, mycelium aseptate or septate. This includes four sub divisions:

1. Sub division: Zygomycotina
   Class 1. Zygomycetes – it includes six orders.,
   Class 2. Trichomycetes – it comprises five orders.
2. Sub division: Ascomycotina: Fungi usually with a septate mycelium producing haploid
   ascospores in sac like cells called asci.
   Class 1. Ascomycetes: Divided into five sub classes:
   Sub class 1. Hemiascomycetidae- comprising three orders.
   Sub class 2. Plectomycetidae- Five orders
   Sub class 3. Hymenoascomycetidae – Ten orders
   Sub class 4. Laboulbeniomycetidae – Two orders
   Sub class 5. Lowloascomycetidae – five orders
3. Sub division 3: Basidiomycotina: Septate mycelium, produces basidiospores, exogenously on
   various types of basidia.
   Class 1. Basidiomycetes: it is split into 3 sub clases:
   Sub class 1. Holobasidiomycetidae
   Sub class 2. Phragmobasidiomycetidae
   Sub class 3. Teliomycetidae
4. Sub division: Deuteromycotina: It includes imperfect fungi in which sexual stage is
   unknown. It comprises a single class.
   Class 1. Deuteromycetes
   Sub class 1. Blastomycetidae
   Sub class 2. Coelomycetidae
   Sub class 3.Hyphomycetidae

Classification based on spore production:

❖ On the basis of the organisation of the vegetative thallus, the morphology of reproductive
structures, the way of spores production and particular life cycle involved the kingdom mycota is
classified into following divisions.

Phycomycetes

• It includes the simplest type of fungi. It is also called as Algae-Fungi because most of the
  characteristics of them are similar to algae like Vaucheria.
• They have simple thallus which is unicellular or coenocytic or aseptate filaments.
• They reproduce asexually by the formation of zoospores or non-motile spores.
• Sexual reproduction is isogamous or heterogamous which takes place by gametangial contact.
• The diploid phase is represented by zygote.
• Phycomycetes has been classified into subclasses: oomycetes and zygomycetes.

Oomycetes

• It range from a primitive unicellular thallus to a profusely branched filamentous mycelium.
• Many members of them are terrestrial and obligate parasites.
• Asexually they reproduce by biflagellate zoospores.
• Oogamous reproduction that involves the fusion of male and female gametes to form oospore.
• Oospore undergoes meioses to produce haploid biflagellate zoospores..
• Examples:
• 1. Late Blight:
• Phytophthora infestans causes late blight of Potato and occasionally of Tomato as well. Blight is the appearance of brownish to black dead areas.
• They are first formed on the mar­gins and tips of leaflets. Later on the whole foliage becomes blighted. Tuber yield is reduced. The surface of the tubers also shows blighting. Irish famine of 1845- 1847 was caused by late blight of Potato.
• 2. White Rust:
• It occurs in cruci­fers and is characterised by the appearance irregular white blisters containing, conidiosporangia on the leaves and stems. White rust is caused by Albugo Candida
• 3. Damping off:
• Pythium debaryanum kills seedlings of a num­ber of plants through collapse of stem just above the ground level.
• 4. Downy Mildew:
• The patho­gen produces a cottony or wooly bloom on the surface of the host. Sclerospora graminicola spreads downy mildew in cereals and green ear disease of Pennisetum typhoides (vem. Bajra). Peronospora parasitica causes downy mildew in a number of plants, e.g., Pea, Mustard, Spin­ach, Onion, etc..

Zygomycetes-The Conjugation Fungi:

• The group is named zygomycetes because a diploid resting spore called the zygospore is formed
  during the life cycle.
• They are mostly saprophytic, some others are parasites on plants and animals.
• The vegetative body is mycelium which is well developed, profusely branched and coenocytic.
• The absence of motile sexual or asexual cells.
• The asexual reproduction takes place by sporangiospores, aplanospores or by conidia.
• Sexual reproduction occurs by conjugation of gametangia resulting in the formation of
  zygospore.
• Examples:
• 1. Squirting Fungus:
• Pilobolus crystallinus is a coprophilous or dung mould in which mature sporangia are thrown away up to a distance of 2m.
• 2. Rhizopus and Mucor:
• Rhizopus stolonifer (= R. nigricans) is popularly known as black bread mould. Mucor caninus or M. mucedo is coprophilous. It is also called dung mould. Rhizopus and Mucor are the common saprotrophic fungi that attack a variety of food stuffs.
• Soft rot or leak disease of Strawberry, Apple, Sweet Potato, etc. is due to Rhizopus. Mucor pusillus causes infection of internal organs in human beings. Absidia corymbifera causes bronchomycosis. Both Rhizopus and Mucor species (e.g., Rhizopus oryzae, Mucor javanicus) are used in alcoholic fermentation. The two also produce a number of organic acids like citric acid, lactic acid and fumaric acid.

Ascomycetes

• The species of ascomycetes are called the sac fungi because they produce sexual pores within the
  sac-like vascus.
• Ascomycetes are mostly terrestrial occurring as saprophytes or parasites.
• They have well-developed, branched, septate mycelium except yeast. Yeast is a unicellular fungus.
• Asexually they reproduce by non-motile spores, conidia, oidia or chlamydospores.
• Sexual reproduction takes place by the fusion of gametangia of opposite mating types.
• There is absence of motile cells.
• Examples:
• 1. Yeasts:
• Yeasts are a group of non-mycelial or pseudomycelial ascomycetes which multiply asexually by budding or fission and where asci are not organised into ascocarps.
• Depending upon the mode of asexual reproduction, yeasts are of three types— budding yeasts e.g. Saccharomyces), fission yeasts (e.g., Schizosaccharomyces) and halobial yeasts (both budding and fission, e.g., Saccharomycoides). Yeasts in which ascus formation is known are named as true yeasts.
• Related forms which resemble yeasts in most character­istics but where ascus formation is not reported are called false yeasts, e.g., Candida, Mycoderma, and Cryptococcus. They are otherwise included amongst deuteromycetes.
• Economic Importance:
• (i) Brewing Industry:
• Under anaerobic conditions sugary so­lutions inoculated with yeasts are converted into alcoholic beverages, e.g., beer, wine, cider, toddy. They are concentrated further to produce rum and whisky. The two common yeasts used by brewing industry are Saccharomyces cerevisiae (Beer or Baker’s yeast) and S. ellipsoidens (Wine Yeast),
• (ii) Baking Industry:
• Kneaded flour is inoculated with Saccha­romyces cerevisiae (Baker’s Yeast). It produces carbon dioxide and alcohol. The two evapo­rate during baking, making the dough soft and spongy,
• (iii) Vitaminised Food:
• Yeast used in brewing industry is regularly harvested and used as vitaminised food,
• (iv) Curing:
• Yeasts are used in curing cocoa beans,
• (v) Spoilage of Food:
• Being saprotrophic, yeasts attack various food stuffs including tomato products, foods having lactic acid and carbonated beverages,
• (vi) Silk Industry:
• Some yeast reduces the yield of silk industry by attacking silkworms,
• (vii) Plant Diseases:
• Species of Nematospora attack Cotton, Tomato and Beans,
• (viii) Human Diseases:
• Candida albicans causes thrush and inflammation of genitalia. Cryptococcus neoformans attacks nervous system producing lesions, meningitis and brain tumour. Torula produces skin nodules and lesions of viscera.
• 2. Aspergillus:
• It is a common green smoky mould which not only contaminates labo­ratory cultures (hence weed of laboratory) but also various food stuffs including bread, butter, cheese, syrups, jams, jellies, textile and leather goods. It causes rotting of dates, figs, pomegranates, cigars and tobacco.
• Some lung (pulmonary aspergillosis) and ear infec­tions are caused by Aspergillus species. Fermentation effected by Aspergillus yields alcohol (Sake of Japan), citric acid, gluconic acid, glycerol, В-complex vitamins, enzymes and antibiotics.
• 3. Penicillium:
• P. chrysogenum yields the antibiotic penicillin. The latter was the first commercial antibiotic. It was formerly obtained from P. notatum. P. griseofulvum produces antifungal drug griseofulvin.
• The fungus is employed in ripening of cheese (camembert and roquefort varieties) and production of organic acids. The fungus is oth­erwise known to spoil food, citrus fruits, apple, grape, paper, wood and ensilage. The blue-green mould appearing on cit­rus fruits is Penicillium.
• 4. Neurospora (Pink Bread Mould):
• N. crassa is often employed in studies conducted in experimental genetics. It is often called “Droso­phila of plant kingdom”.
• 5. Erysiphe:
• The fungus produces powdery mildew (fungal disease in which pathogen results in a powdery coating on the surface of the host), e.g., Erysiphe graminicola (E. graminis, on cereals like Wheat, Barley), E. polygoni (on legumes like Pea).
• 6. Claviceps:
• Claviceps purpurea produces ergot of rye and other cereals in which ears come to have sclerotia of the fungus. Eating of infected cereals produces ergotism. Ergotism is of two types, gangrenous and spasmodic. The sclerotia contain a number of alkaloids, the most important being lysergic acid.
• Ergot is used as a medicine to control migraine, enlarged prostate glands and uterine haemorrhage after child birth. These days lysergic acid is pre­pared through fermentation activity of C. paspali. LSD, a hallucinogen, is D-lysergic acid diethylamide-15.
• 7. Sclerotinia:
• S. fruticola causes brown rot of Peach, Plum and Pear.
• 8. Cup Fungi:
• The ascocarp is cup-shaped, e.g., Peziza.
• 9. Morels:
• Morels are ascomycetes with edible ascocarps that have fleshy sponge-like conical cap or pileus and a stalk like stipe, e.g., Morchella esculenta (vern. Gucchi), M. crassipes, M. deliciosia.
• 10. Truffles:
• They are edible ascomycetes with tuber-like subterranean ascocarps that are often dug out with the help of trained dogs and pigs, e.g., Tuber uncinatum, T. aestivum.

Basidiomycetes

• The members of basidiomycetes are saprophytic or parasitic. The group is named basidiomycetes
  as they produce the basidiospores at the club-shaped basidium during sexual reproduction.
• Mycelium is highly developed, profusely branched and septate.
• The mycelia are differentiated into two mating types; (+ve) and (-ve).
• There are two kinds of mycelium; primary mycelium and secondary mycelium.
• Asexual reproduction takes place by fragmentation, budding, oidia, conidia or chlamydospore.
• The dikaryotic cell is formed during sexual reproduction.
• The absence of motile cell throughout the life cycle.
• These are the most advanced fungi as their fructifications are often large and prominent.
• Examples:
• 1. Rusts:
• They are characterised by the formation of rusty pustules containing the spores. A basidiocarp is absent, (i) Puccinia graminis tritici — black rust of wheat, (ii) Puccinia glumarum — yellow rust of wheat, (iii) Hemileia vastatrix — leaf rust of coffee.
• 2. Smuts:
• They produce thick-walled black-coloured resting spores called smut spores (= teleutospores = chlamydospores). Smuts are of two types, covered and loose. In covered smuts the spore mass remains within the host till the latter is set free, e.g. Ustilago maydis (smut of corn), Tilletia tritici (bunt or stinking smut of wheat). In loose smut the spores are exposed while attached to the host, e.g. Ustilago tritici (loose smut of wheat).
• 3. Mushrooms:
• They are edible and nonedible agaric ales which possess umbrella like basidiocarp the edible mushrooms generally possess coloured basidiospores. Common examples are Agaricus campestris, Agaricus brunnescens (= A. bisporus), Volvariella volvacea (Paddy Straw Mushroom), Lentinus edodes (Shiitake Mushroom).
• 4. Toadstools:
• Toadstools are nonedible, often poisonous mushrooms which generally have white spores. Amanita caesarea (Caesaer’s Mushroom) was used in poisoning Roman emperor Caesar. The other toadstools are Amanita phalloides (Death Cap) and A. muscaria (Fly Agaric).
• 5. Bracket Fungi (Shelf Fungi):
• The basidiocarps or fructifica­tions appear on tree trunks, logs, lumber, etc. just as brackets or shelves, e.g. Fomes applanatus (peren­nial), Polyporus sulphureus (annual).
• 6. Puffballs:
• The basidiocarp is a stalked rounded structure which on ripening sends out puffs of spores. The fructification may grow above or below the substratum. Puffballs are odoriferous. They are edible in the young state, e.g. Lycoperdon oblongisporum, L. giganteum.
• 7. Armillariella (= Armillana):
• A. mellea (Honey Mushroom) is an edible mushroom which is a serious root parasite of both hardwoods and conifers. The fungus sends rhizomorphs into the phloem of the host and hence block the food supply.
• 8. Hallucinogens:
• Psilocybe mexicana (Sacred Mushroom) has hallucinating properties similar to LSD. It is used by Mexican Indians for certain religious ceremonies.

Deuteromycetes (The Imperfect Fungi)

• Deuteromycetes compromises more than 17000 species of the diverse habits and habitats. It is
  considered as an artificial class of fungi.
• The fungi are saprophytes as well as parasites.Parasitic fungi cause serious diseases to plants,
  animals including human beings.
• Some of them are unicellular while others are multicellular.
• They reproduce asexually by conidia along with some other types of spores.
• The sexual reproduction is entirely absent.
• The asexual stage or imperfect stage in Deuteromycetes is well defined. But the sexual or perfect
  stage is absent in life cycle, therefore, they are called ‘Fungi Imperfecti’.
• Examples:
• 1. Red Rot:
• Colletotrichum falcatum produces red rot of sugarcane which is conspicuous on leaf midribs as well as in canes. It reduces juice content of canes and brings about withering of leaves. The fungus develops sickle-shaped conidia. The perfect stage is Glomerella tucumanensis.
• 2. Helminthosporium:
• Helminthosporium oryzae causes leaf spot disease of rice commonly called sesame or brown leaf spot of rice. It caused Bengal fam­ine of 1942-43 and similar conditions in Krishna-Godavari area in 1989-1990. The perfect stage of the fungus is Cochliobolus miyabeanus. The conidia are 5-10 septate.
• 3. Early Blight:
• Alternaria sotani causes early blight of Potato and Tomato. The leaves develop small oval brown spots with concentric rings. The leaves as well as the branches wither and fall down. The conidia are beaked bottle-like multi-septate with a number of transverse and a few longitudinal septa.
• 4. Tikka Disease:
• Circu­lar necrotic dark brown or blackish leaf spots develop in groundnut due to Cercospora (e.g. C. personata). The conidia are septate and filamentous. The perfect stage is Mycosphaerella (e.g., M. berkeleyii).
• 5. Wilts:
• Many economically important plants (e.g., Potato, Tomato, Cotton, Banana, Flax, Pigeon Pea) show sudden signs of wilting due to blockage of tracheary elements by growth of fungus Fusarium especially F. oxysporum. The fungus shows three types of spores — chlamydospores, micro conidia and macro conidia.
• 6. Gibberellins:
• They were first discovered in the ex­tracts of Fusarium moniliformae growing on rice (bakane or foolish disease of rice). The perfect stage of fungus is Gibberella fujikuroi. Gibberellins are natural plant growth hormones.
• 7. Trichoderma:
• It is a soil fungus used in biological control of other fungi as it produces allelochemics against them. If the fungus happens to pass into human alimentary canal it produces leucopenia called alimentary canal aleukia.

Classification based on medically important fungi

Mycoses are classified as superficial, cutaneous, subcutaneous, or systemic (deep) infections
depending on the type and degree of tissue involvement and the host response to the pathogen.
a. Superficial mycoses (or tineas): Occur in the tropics and are restricted to the outer surface of
the hair and skin, e.g., Piedraia hortae.
b. Cutaneous mycoses: There are three genera of fungi (Microsporum, Trichophyton and
Epidermophyton) that commonly cause disease in the non-living tissues of skin, hair, or
nails/claws of people and animals, by growing in a zone just above where the protein keratin is
deposited.
c. Subcutaneous mycoses: They are normally saprotrophic inhabitants of soil, particularly in
tropical and subtropical areas of Africa, India and South America.
d. Systemic mycoses are infections that affect the whole body. We divide these into mycoses due
to primary (usually dimorphic) virulent pathogens, and those due to opportunistic pathogens.

Classification based on route of acquisition

a. Infecting fungi may be either exogenous or endogenous.
b. When classified according to the route of acquisition, a fungal infection may be designated as
exogenous or endogenous in origin.
c. If classified as exogenous, an infecting organism may be transmitted by airborne, cutaneous, or
percutaneous routes.
d. An endogenously-acquired fungal infection may be acquired from colonization or reactivation
of a fungus from latent infection.

Classification based on virulence

• Primary pathogens can establish infections in normal hosts.
• Opportunistic pathogens cause disease in individuals with compromised host defense
• mechanisms.

• Deep mycoses are caused by primary pathogenic and opportunistic fungal pathogens.
• The primary pathogenic fungi are able to establish infection in a normal host; whereas,
  opportunistic pathogens require a compromised host in order to establish infection (e.g., cancer,
  organ transplantation, surgery, and AIDS).
• The primary deep pathogens usually gain access to the host via the respiratory tract.
  Opportunistic fungi causing deep mycosis invade via the respiratory tract, alimentary tract, or
  intravascular devices.
• The primary systemic fungal pathogens include Coccidioides immitis, Histoplasma capsulatum,
  Blastomyces dermatitidis, and Paracoccidioides brasiliensis.
• The opportunistic fungal pathogens include Cryptococcus neoformans,
  Candida, Aspergillusspp., Penicillium marneffei, the Zygomycetes, Trichosporon beigelii,
  and Fusarium spp.