Division Eumycota: Meaning, Characteristics and Classification

In this article we will discuss about:- 1. Introduction to Division Eumycota 2. Characteristics of Division Eumycota 3. Classification.

Introduction to Division Eumycota (True Fungi):

The members of the division Eumycota are called true fungi. It is a very large group consists of approximately 75,000 known species, but this number should be much more as more species are regularly being added in the list due to the discovery of new species from different corners of the world.

The thalli of Eumycota usually do not posses Plasmodia or pseudoplasmodia. Members are unicellular or filamentous with definite cell wall. Spores of many fungi act as common conta­minants of our food. They cause diseases of both plants and animals including human beings. They are also useful in many respects.

Characteristics of Division Eumycota (True Fungi):

The important characteristics of the division Eumycota are:

1. The plant body is thalloid and commonly consists of profusely branched filament, the mycelium, except a few unicellular mem­bers (Saccharomyces etc.). In filamentous body, unit branch of the mycelium is called hypha (pi. hyphae).

2. The mycelial plant body may be aseptate i.e., coenocytic (lower fungi, Mastigomycotina and Zygomycotina) or septate (higher fungi, Ascomycotina, Basidiomycotina and Deuteromycotina).

3. Septa, when present, are perforated. The pores are of different types: micropore (Geotri­chum), simple pore (most of the Ascomyco­tina and Deuteromycotina) or dolipore (Basidiomycotina except rusts and smuts).

4. The hyphal wall is made up of fungal cellu­lose i.e., chitin; but in some lower fungi (members of Oomycetes), cell wall com­posed of cellulose or glucan.

5. Growth of hyphae is apical.

6. The cells are haploid, dikaryotic or diploid. Diploid phase is ephemeral (short lived). The dikaryotic phase persists for longer period in higher fungi (members of Basidiomycotina).

7. Most of the fungi are eucarpic in nature.

8. Reproduction takes place by all the three means: vegetative, asexual and sexual. (Sexual reproduction is absent in Deutero­mycotina).

9. Spores are either motile (Mastigomycotina) or non-motile (in rest members).

10. During sexual reproduction, plasmogamy takes place through: Gametic copulation (Synchytrium), Gametangial contact (Pythium, Phytophthora), Gametangial copulation (Rhizopus, Mucor etc.), Spermatization (Puccinia) and Somatogamy (Agaricus, Polyporus).

11. Progressive reduction of sex is observed from lower to higher form.

12. Parasitic members cause diseases having both harmful and useful activities.

Classification of Division Eumycota:

The classification of Eumycota by Ainsworth (1973) is given below:

Key to subdivision of Eumycota:

1. Motile cell (zoospores) present, perfect state spores typically oospores…..………… Mastigomycotina.

Motile cell absent…………………………2

2. Perfect state absent… Deuteromycotina perfect state present………………………………3

3. Perfect state spores zygospores………………………………………………Zygomycotina.

Zygospores absent……………………….4

4. Perfect stste spores ascospores…………..………………………..Ascomycotina.

Perfect state spores basidiospores….………………………. Basidiomycotina.

1. Subdivision Mastigomycotina (Zoosporic Fungi):

The subdivision Mastigomycotina is com­monly known as zoosporic fungi.

The important characteristics of Mastigo­mycotina are:

i. The Mastigomycotina are zoosporic fungi, adapted mostly in aquatic habitat.

ii. Three types of zoospores are common in this group.

These are:

(a) Laterally biflagellate,

(b) Posteriorly uniflagellate, and

(c) Anteriorly uniflagellate type having “9 + 2” arrange­ment of component fibrils.

iii. Members of this group vary from unicellular plant body (with or without rhizoid) to fila­mentous coenocytic mycelium.

iv. Sexual reproduction takes place by gametic copulation, gametangial copulation and gametangial contact.

Ainsworth (1973) classified the subdivision Mastigomycotina into three classes:

A. Chitridiomycetes,

B. Oomycetes.

Key to classes of Mastigomycotina:

a. Zoospores uniflagellate.

b. Flagellum posteriorly placed and whiplash type … Chitridiomycetes.

bb. Flagellum anteriorly placed and tin­sel type … Hyphochytridiomycete.

aa. Zoospores biflagellate (one whiplash and other one tinsel type)…Oomycetes.

A. Class. Chitridiomycetes:

Their main distinguishing characteristics are:

i. The vegetative body is unicellular or chain of cells attached with the substratum by rhizoids.

ii. Cell wall is mainly made up of chitin and glucans.

iii. The plant body is normally haploid, except Allomyces.

iv. Asexual reproduction takes place by zoospores produced in zoosporangium; zoospores are uniflagellate, flagellum whiplash type and posteriorly placed.

v. Sexual reproduction takes place by piano- gametes developed in gametangia. The fused gametes form zygote. After resting period, it undergoes meiosis and forms new haploid thallus.

Members of this group are mostly aquatic. Some of them are terrestrial and parasitic. Important parasitic members are Synchytrium endobioticum causes wart disease of potato; Olpidium brassicae, in roots of Crucifers; Urophlyctis alfalfae causes crown wart of alfalfa (Medicago); and Physoderma maydis causes brown spot of maize.

Coelomomyces anophelescia is an endoparasite on mosquito larvae and can be utilized for the biological control of Anopheles mosquito.

B. Class. Oomycetes:

The members are mostly aquatic, either free- living or parasitic on water molds, algae and small animals. Some are terrestrial and few are parasitic on higher plants. The class Oomycetes is characterised by oogamous type of sexual reproduction.

The main distinguishing characteristics are:

i. Members of this class are generally aquatic, but some are terrestrial, grows saprophyticaily on soil or parasitically on shoots of higher plants.

ii. The plant body ranges from unicellular, holocarpic, endobiotic parasites to well- developed coenocytic and branched myce­lium.

iii. The cell wall is composed mainly of cellulose-glucan and devoid of chitin.

iv. Asexual reproduction takes place by biflagellate zoospore without cell wall. The zoospores may be either pear-shaped with anteriorly placed flagella (primary) or reni-form with laterally placed flagella (secon­dary). The flagella are unequal in length, the shorter one tinsel (Flimmer or Pantonematic) type and longer one whiplash (Peitschen or Acronematic) type. Some members produce conidia as asexual spore.

v. Members of Oomycetes are generally eucar­pic, except Lagenidiales those are holocarpic.

vi. Sexual reproduction is of oogamous type. The non-motile gametes are produced in male (antheridium) and female (oogonium) gametangium. The male gametes are trans­ferred to the egg through fertilisation tube, results in the formation of oospore.

vii. The vegetative thallus is diploid and meiosis takes place in gametangium rather than in zygote.

Some important parasitic members of this group are:

i. Pythium. Different species of Pythium cause foot rot, fruit rot, rhizome rot and damping off (detail in Table 4.1).

ii. Phytophthora. Different species of Phytoph­thora cause stem and leaf blight, foot rot, leaf rot, corm rot, fruit rot etc. (detail in Table 4.2).

iii. Plasmopara. P. viticola causes downy mildew of grape vine.

iv. Albugo. Different species of Albugo cause white rust disease of different hosts like crucifers (cabbage, Brassica, radish, rurnip etc.), spinach, sweet potato, morning glories etc. The A. Candida is very common causing white rust of crucifers.

v. Saprolegnia. S. parasitica, a parasite on fish, is an aquatic member.

2. Subdivision. Zygomycotina:

The fungi belonging to this group are gene­rally terrestrial and they produce zygospore (Gr. zygos — yoke; Spora — seed, spore) after sexual reproduction.

The Important Characteristics of Zygomycotina are:

i. The thallus is normally haploid, consisting of coenocytic mycelium and its cell wall con­tains chitin and chitosan.

ii. The mycelium contains cell organelles like other fungi, except typical golgi bodies and centriole.

iii. Asexual reproduction takes place by aplanospores.

iv. Sexual reproduction takes place by game­tangial copulation, resulting in the formation of zygospore.

Ainsworth (1973) classified the subdivision Zygomycotina into two classes:

i. Zygomycetes, and

ii. Trichomycetes.

Key to Classes of Zygomycotina:

a. Saprophytic or, if parasitic or predaceous, having mycelium immersed in host tissue Zygomycetes.

aa. Parasitic or commensals within the digestive tract of living arthopods Trichomycetes.

The subdivisions Mastigomycotina and Zygomycotina of G. C. Ainsworth (1973) were earlier included under the class Phycomycetes by Gwynne-Vanghan and Barnes (1926).

The main distinguishing characteristics of the class Phycomycetes are:

i. The members of the class Phycomycetes may be either aquatic (Saprolegnia para­sitica), saprophytic (Mucor) or para­sitic (Phytophthora, Pythium) on higher plants.

ii. The thalloid plant body is very simple, ranges from isolated cell to a profusely branched coenocytic (nonseptate) myce­lium. Septa may form in the older plants and also at the base of sex organs.

iii. Reproduction takes place by vegetative, asexual and sexual means.

(a) Vegetative reproduction takes place by the formation of oidia, budding and fragmentation.

(b) Asexual reproduction takes place by zoospores or aplanospore produced enciogenously in sporangia and by conidia developed exogenously on conidio­phore (Albugo). The zoospores are either uni- or biflagellate.

(c) Sexual reproduction takes place by planogametic copulation (isogamy in Synchytrium; anisogany in Allomyces and oogamy in Monoblepharis, gametangial contact (Phytophthora, Pythium) and gametangial copulation (Mucor, Rhizopus).

The product of sexual fusion may be zygote (Synchytrium, Allomyces), zygospore (Rhizopus, Mucor) or oospore (Pythium, Phytophthora), usually secretes a thick wall around itself and undergoes rest. On germi­nation, it may give rise to meiozoospores or meioaplanospores.

3. Subdivision. Ascomycotina (Sac fungi):

The Ascomycotina (Gr. askos— sac or blad­der; mykes — fungi), commonly known as “sac fungi”, is the largest group under the Kingdom Fungi, comprised of six classes and about 30,000 species. Majority of the members are terrestrial, although many members live in water. They may be saprophyte or parasite, cause diseases. The most important and interesting members are the yeasts used in bakery and alcohol industry.

Claviceps purpurea, the causal agent of ergot disease of rye, develops sclerotia that contain a lot of alkaloids including L.S.D. (lysergic acid diethylamide), the well known hallucinogenic drug and Ergometrine, a popular medicine.

Ergometrine and its semisynthetic analogue, methyl ergometrine have prominent uterine action, commercially used as methyl ergometrine maleate with trade names EMATRIN, ERGOLIN, METHERGIN, UTERGIN, UTROWIN etc. or ergometrine maleate with trade names ERGO- METRIN and LERIN as tablet (0.125 mg) or injec­tion (0.2 mg/ml), which control haemorrhage of mother during childbirth, but the drugs raise blood pressure and decrease milk secretion.

The wonder drug penicillin is an important antibio­tic, produced by Penicillium notatum, discovered by Sir Alexander Fleming in 1929. Later, it was also isolated from P. crysogenum and P. italicum.

The Important Characteristics of Ascomycotina are:

i. Vegetative body is unicellular or commonly well-developed, branched septate mycelium with uni- or multinucleate cells having per­forated septa.

ii. Mostly, the cell wall is composed of chitin and glucans, but in unicellular form, it is composed of glucans and mannans.

iii. Vegetative reproduction takes place by frag­mentation (in filamentous form), fission and budding (in unicellular form).

iv. Asexual reproduction takes place by non- motile spores, such as conida, oidia and chlamydospores.

v. Sexual reproduction takes place by gametangial copulation (Saccharomyces), gametangial contact (Penicillium), somatogamy (Morchella) or spermatization (Polystigma).

vi. Complete absence of motile structures.

vii. The product of sexual reproduction is the ascospores grown inside a small specialised sac-like structure, called ascus.

viii. The fruiting bodies (inside which asci are developed) are the ascocarps. The ascocarps may be cleistothecium (Penicillium), apothecium (Ascobolus), perithecium (Daldenia) or ascostroma (Elsinoe veneta).

Ainsworth (1973) classified the sub­division Ascomycotina into six classes, namely:

i. Hemiascomycetes,

ii. Loculoascomycetes,

iii. Plectomycetes,

iv. Laboulbeniomycetes,

v. Pyrenomycetes, and

vi. Discomycetes.

Key to Classes of Ascomycotina:

A. Ascocarps and ascogenous hyphae absent; thallus mycelial or yeast like.

………………………. Hemiascomycetes

AA. Ascocarps and ascogenous hyphae present; thallus mycelial.

B. Asci bitunicate, ascocarp an ascostrama.

…………………… Loculoascomycetes

BB. Asci typically unitunicate, if bitunicate, ascocarp an apothecium.

C. Asci evanescent, scattered within the astomous ascocarp which is typically a cleistothecium; ascospores aseptate.

……. Plectomycetes.

CC. Asci regularly arranged within the ascocarps as a basal or peripheral layer.

D. Exoparasites of arthopods; thallus reduced; ascocarp a perithe­cium; asci inoperculate.

……. Laboulbeniomycetes.

DD. Not exoparasites of arthopods.

E. Ascocarp typically a perithe­cium which is usually ostiolate (if astomous, asci not evanescent); asci inopercu­late with an apical pore or slit… Pyrenomycetes.

EE. Ascocarp an apothecium or a modified apothecium, frequently macroscopic, epigean or hypogean; asci inoperculate or operculate. . Discomycetes.

Development of Ascus:

In the subdivision Ascomycotina, the asci develop after sexual reproduction which gene­rally contain eight ascospores, but their number may be four (Saccharomyces cerevisiae, Saccharomycodes ludwigii) or many (Dipodascus uninucleatus).

Asci may be cylindrical, globose or club-shaped (Fig. 4.32). Based on the wall struc­ture and mode of dehiscence, the asci may be differentiated as prototunicate, unitunicate and bitunicate.

The prototunicate asci (Endomyces, Saccharomyces etc.) have a thin delicate wall. Both unitunicate and bitunicate asci have two layered wall.

In unitunicate asci (Peziza, Ascobolus etc.), both the layers remain together even during spore release, but in bitunicate asci (Pleospora, Melaspilea etc.) the inner wall is pro­jected out during spore liberation, while outer wall remains in its earlier position. Asci may develop either directly or indirectly.

A. Direct Development of Ascus:

In unicellular members like Saccharomyces and related genera, the two compatible cells come close to each other (Fig. 4.29A, B). The cells undergo plasmogamy by dissolution of their common wall and the two haploid nuclei come close to each other and undergo fusion (karyogamy) results in the formation of a diploid nucleus, the zygote (Fig. 4.29C-F).

The zygote containing cell enlarges and forms an ascus mother cell. The diploid nucleus undergoes first meiotic division followed by single mitotic division, results in the formation of eight nuclei (Fig. 4.29G-I). The nuclei along with some cytoplasm form ascospores. In some cases, mitotic division does not take place after meiosis and forms four ascospores (Saccharomyces cerevisiae, Saccharomycodes ludwigii) in an ascus.

In filamentous members like Dipodascus uninucleates (Fig. 4.30), gametangia developed from vegetative mycelium undergo plasmogamy and one nucleus from each gametangium under­goes karyogamy results in the formation of a single zygote. The zygote undergoes repeated mitotic division after meiosis and forms nume­rous ascospore in an elongated ascus.

B. Indirect Development of Ascus:

In filamentous members like Penicillium, Peziza, Pyronema (Fig. 4.31) and many others, ascus develops in indirect way. The transfer of male nuclei from antheridium to ascogonium takes place by plasmogamy and both the nuclei of opposite mating arrange themselves in pairs, called dikaryon. Karyogamy maintains a long time interval with plasmogamy.

From the wall of the ascogonium a number of ascogenous hyphae develop showing a dikaryon condition (Fig. 4.31 B, C). The tip of the ascogenous hyphae bends down to form a crozier or hook (Fig. 4.31 D). Nuclear division starts simul­taneously with the crozier formation. Thus four nuclei are formed by mitosis inside the crozier.

Two septa are laid down that demarcate uni­nucleate terminal cell, binucleate (of opposite mating) penultimate cell and uninucleate basal stalk cell (Fig. 4.31 E, F). The binucleate penulti­mate cell behaves as ascus mother cell. The wall of ascus mother cell extends more in length than the breadth, thus forms an elongated ascus.

Simultaneously, both the nuclei of ascus mother cell fuse and form diploid nucleus (Fig. 4.31 H- K), which undergoes first meiotic division and then mitotic division results in the formation of eight nuclei. The cytoplasm accumulates around each nucleus to form ascospore (Fig. 4.31 L, M). Division may take place both in nucleus and cytoplasm of an ascus results in the formation of 2-celled ascospore.

The apical cell of ascogenous filament bends and may fuse with the basal cell and the region extends again and forms new binucleate penultimate cell as before (Fig. 4.31 F-K). This process may repeat several times and a cluster of asci may develop.

Ascospores:

Ascospores are produced in ascus (Fig. 4.32) and may arrange irregularly or in uniseriate (single row), biseriate, inordinate or fascicu­late manner (Fig. 4.32). The ascospores may be colourless or are variously coloured. They may be of various shapes, ranges from globose to narrow thread-like. Their wall may be smooth or variously ornamented.

Ascocarps:

The asci become naked (Fig. 4.33A, B) in Hemiascomycetes ‘(Saccharomyces, Schizosaccharomyces, Taphrina, etc.), but in others they are found intermingled with mycelium and form ascocarps of different shapes such as cleistothecium (globose), perithecium (flask-shaped), apothecium (saucer-shaped) or ascostroma (looks like perithecium but lacks its distinct wall and also differs in development).

In cleistothecium the asci may be arranged scatteredly (Penicillium) or are arranged in tuft at the base (Erysiphe, Fig. 4.33C). In Perithecium (Fig. 4.33D, E), the asci develop from the bottom and are intermingled with sterile mycelia called paraphyses (Members of Pyrenomycetes, Claviceps, Xylaria etc.).

Asci are arranged in a layer on the top of the exposed hymenial surface mixed with paraphysis in Apothecium (Fig. 4.33G, H) fruit- body (Ascobolus, Peziza), and lastly Ascostroma (Fig. 4.33F) may contain one or more cavities, that looks like perithecium, where asci are deve­loped from the base. This type of ascocarp is also known as Pseudothecium (Pleospora, Leptosphaeria etc. under Loculoascomycetes).

4. Subdivison Basidiomycotina:

The members included in the subdivision Basidiomycotina are characterised by the formation of basidiospores exogenously on the basidium (PI. basidia; Gr. basidion — a small base) and absence of flagellated structure. The subdivision included about 500 genera with more than 16,000 species.

The members include rusts, smuts, mushrooms, puff balls, toad stools, bracket fungi etc. Rust (Puccinia spp.) and smuts (Ustilago spp.) cause disease of crop plants resulting heavy financial losses in different parts of the world.

Mushrooms [Volvariella volvacea, Agaricus brunnescens (syn. A. bisporus), A campestris] are used as nutritious and healthy food for mankind. Some members like Amanita phalloides, A. verna etc., are deadly poisonous, while others like Psilocybe mexicana produce two indole deri­vatives Psilocybin and Psilocin that have hallu­cinogenic properties.

The bracket fungi like Polyporus betulinus, P. squamosus and several others cause damage of forest trees as parasite and to wooden logs as saprophyte. Some others like P. umbellatus, P. frondosus and P. leucomelas are edible.

The important characteristics of Basidio­mycotina are:

i. Presence of well-developed, branched and septate mycelium having simple (e.g., Ustilaginales and Uredinales) or dolipore (e.g., Auriculariaceae, Aphyllophorales and Agaricales) septum (Fig. 4.2B & 4.2D).

ii. The mycelial cells may contain one nucleus, called monokaryotic i.e., primary mycelium or two nuclei, called dikaryotic i.e., secon­dary mycelium. The secondary mycelia may organise and form fruit body, called tertiary mycelium.

iii. The cell wall is mainly composed of chitin and glucans.

iv. Reproduction.

(a) Vegetative reproduction takes place by budding and fragmentation.

(b) Asexual reproduction takes place by conidia, oidia, or chlamydospores that are absent in some higher taxa of this subdivision.

(c) Sex organs are absent. During sexual reproduction, the dikaryotic cell is formed by somatogamy, spermatization or by buller phenomenon. The dikaryo­tic phase persists for long period of time. Karyogamy occurs in basidium mother cell and forms diploid nucleus, which is ephemeral (short-lived). 4-haploid basidiospores are formed by meiosis.

(d) Basidiospores are developed exogenously on the horn-shaped structure, called sterigmata (generally 4) on the basidium.

v. Basidia are of two types. Holobasidium (aseptate) e.g.,, Agaricus, Polyporus etc. (Fig. 4.56A) and Phragmobasidium (septate) e.g., Puccinia, Ustilago (Fig. 4.56B) etc.

vi. Except in lower forms (Puccinia, Ustilago), secondary mycelia by aggregation form fruit body, called basidiocarp (Agaricus, Polyporus etc.). It has the spore bearing structure, called basidium. The number of spores on each basidium is commonly four, but 2 or more than 4 are also reported.

Growth of Mycelium by Cell-Division:

The secondary mycelium has cells with two nuclei of opposite mating (Fig. 4.57A). The api­cal cell of secondary mycelium divides by the formation of lateral projection known as Clamp connection. During cell division a short backwardly directed outgrowth develops from lateral wall, known as clamp.

Out of two nuclei, one migrates towards the clamp (marked as hollow) and the other one (marked as solid) remains in the cell (Fig. 4.57B). Both the nuclei then undergo mitotic division (Fig. 4.57C) forming four nuclei. Out of two (marked as hollow) nuclei, one remains in clamp and the other goes back to the apical region of the cell.

The remaining two (marked as solid) nuclei in the cell are distributed towards apical and basal region. Thereafter, two septa are developed in such a way that one sep­tum separates the clamp and the other develops at the bottom level of clamp outgrowth, results in the formation of three cells; uninucleate clamp, uninucleate subterminal cell and binu­cleate (dikaryotic) terminal cell (Fig. 4.57D). During this time, the clamp grows and touches the wall of subterminal cell.

The wall of the subterminal cell and clamp at the point of con­tact dissolves and the nucleus of clamp migrates to the subterminal cell and becomes dikaryotic (Fig. 4.57E, F). Thus two dikaryotic cells are formed. This process repeats several times and thus the growth continues.

5. Subdivision. Deuteromycotina:

The subdivision Deuteromycotina is also known as Fungi imperfecti or Waste Box Fungus, comprising of about 600 genera and over 20,000 species. This group includes such fungal members where perfect or sexual stage is not known and only the imperfect or asexual stage is recorded.

In other ways, due to lack of knowledge on sexual reproduction they could not be placed in the well-defined groups such as Mastigomycotina, Zygomycotina, Ascomycotina or Basidiomycotina and have been placed in a separate group, Deuteromycotina. C. T. Ingold called Deuteromycotina the “dust bin” group because of their doubtful systematic position.

This group has been created by the tempo­rary assemblage of fungal members by placing them in proper class after gaining knowledge on their perfect stage.

Possibly, almost all fungi under Deutero­mycotina are the members of Ascomycotina, evidenced by the similarity between the conidial stage of Deuteromycotina and Ascomycotina, lack of aseptate mycelium, the characteristic of Mastigomycotina and Zygomycotina; and the lack of clamp connection, the characteristic of Basidiomycotina.

It is thought that they are mostly the members of Ascomycotina which either did not evolve sexual reproduction or lost them in course of evolution. In most of the cases- it was found that the members of Deuteromyco­tina have to be shifted to Ascomycotina after gaining knowledge and finding similarity with sexual or perfect stage.

Alexopoulos and Mims (1979) considered the Deuteromycetes as “conidial stages of Ascomycetes or more rarely Basidiomycetes whose sexual stages have not been discovered or do not exist”.

The important characteristics of Deutero­mycotina are:

i. The members of this group are either sapro­phytes or parasites.

ii. The vegetative body is mycelial and com­posed of profusely branched and septate hyphae with perforated septa and their cells are usually multinucleate.

iii. In parasitic species, the hyphae grow intra- or intercellularly.

iv. They reproduce only by asexual methods and the sexual stages are not known.

v. The asexual reproduction takes place commonly by conidia, or by blastospores, chlamydospores and arthrospores. The coni­dia are developed exogenously on conidiophores.

The conidiophores are either free or grouped together to form specialized struc­tures, such as synnemata (sing, synnema) and sporodochia (sing, sporodochium) or pro­duced in fructification known as acervuli (sing, acervulus) or pycnidia (sing, pycnidium).

vi. Many genera of the class exhibit genetic variation as a result of heterokaryosis and parasexuality.

Perfect states along with subdivisions of some imperfect fungi are given in Table 4.10.

Classification:

Ainsworth (1973) classified the subdivision Deuteromycotina in three distinct classes; Blastomycetes, Hyphomycetes and Coelomycetes.

Key to Classes of Deuteromycotina:

1. Budding (Yeast or Yeast-like) cells with or without pseudomycelium.

True mycelium lacking or not well-developed………………………. ……………………. Blastomycetes.

Mycelium well-developed, assimilative bud­ding cells absent 2.

2. Mycelia sterile or bearing asexual spore directly or on conidiophore in various aggre­gation but not in pycnidia or acervulus ……………………… Hyphomycetes

Conidia in pycnidia or acervulus ………………………………………………………………… Coelomycetes.

Later, Hawksworth et al., (1983) recognised only two classes: Hyphomycetes and Coelo­mycetes.

Economic Importance:

The class Deuteromycotina has great eco­nomic importance. Some members cause different plant diseases, others cause several diseases of human being, and still others are very useful in controlling a number of soil borne plant diseases.

a. Plant Pathogens:

A number of members cause diseases of different plants. These include leaf spot (blast of rice, Pyricularia oryzae; leaf spot or tikka disease of ground nut, Cercospora personata), blight (early blight of potato, Alternaria solani), blotch (leaf blotch of wheat, Septoria tritici), wilt (wilt of Pigeon pea, Fusarium udum), anthracnose (Anthracnose of mango, Colletotrichum gloeosporioides) etc.

b. Human Pathogens:

Animals including human beings are affected by different pathogens causing different diseases. These are ringworm (Epidermophyton floccosum and Microsporum audowinii), athlete’s foot (Trichophyton gypseum and T. purpurium), monilasis (candida albicans) etc.

c. Biological Control:

Several members are able to control nematode diseases-by trapping the nematodes with their sticky mycelium or loops to which nematodes adhere or trap and then the other hyphae invade and digest them. Thus, these members help in redu­cing the disease by killing the nematode, e.g. Arthrobotrys oligospora, Dactylella cionopaga.