Diversity of Microbes and Cryptograms

Transcription

1 Diversity of Microbes and Cryptograms Fungi 1 D.J. Bagyaraj 1 and J. Arpana 2 1. Dept of Agril. Microbiology University of Agricultural Sciences, GKVK, Bangalore Centre for Natural Biological Resources and Community Development (CNBRCD), #41, RBI colony, Anand Nagar, Bangalore Date of submission: 23/03/2006 Significant Key words: Fungi, Myxomycetes, Eumycetes, Oomycetes, Zygomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes, Pythium, Phytophthora, Mucor, Yeast, Saccharomyces, Aspergillus, Eurotium, Chaetomium, Peziza, Agaricus. Contents: General Characteristics Classification & Economic Importance Mastogomycotina Zygomycotina Basidiomycotina Deuteromycotina 1

2 FUNGI Man s interest in fungi started with the observation of the beautiful, umbrella shaped mushrooms and toad stools growing on soils forming fairy rings. The fungi (sing., fungus) are a distinct group of organisms that are neither plants nor animals. The name of the fungi derived from the most obvious representatives, the mushrooms (Greek- mykes, Latin- fungus). They are eukaryotes and share with plants the possession of a cell wall, liquid filled intracellular vacuoles, microscopically visible streaming of the cytoplasm and lack of motility. However, they do not contain photosynthetic pigments and are chemo-organotrophs. Most of them grow aerobically and obtain their energy by oxidation of organic substances. Compared to the plants, which are organized into stems, roots and leaves, fungi show only very limited morphological differentiation and practically no functional differentiation. Fungi are diverse organisms. There are approximately 70,000 known species of fungi (and probably 10 to 20 times more undiscovered species) found in such varied environments as tropical forests, oceans and deserts. Many fungi adapt to ph extremes and are found in hot or cold climates, although they are not as heat or cold resistant as procaryotes. Fungi are primarily terrestrial heterotrophic organisms; their principle role being the decomposition of organic matter. Fungi along with the bacteria are considered to be the decomposers of the biosphere. Because they most often live on nonliving organic matter, fungi are called saprophytes (Greek: sapros-rotten, phyton- plant). The products released by the decaying action of fungi from their metabolism of organic matter are returned to the environment to be used once again by other organisms. Fungi are also important in industry. Yeasts, a type of fungus, are used in baking, and in wine and brewery industries for the fermentation of sugars into carbon di oxide and ethanol. Mushrooms, another group of fungi, are a source of food. Other fungi are important for cheese and antibiotic production. Fungi can be destructive causing great economic loss. Pathogenic fungi cause many plant diseases (wheat rust, corn smut, potato blight, root rot and stem rot) some human diseases (ringworm, athletes foot and histoplasmosis) and some animal diseases (mange in dogs and cats). Fungi that flourish in moist, warm climates are responsible for the destruction and decay of wood, clothing and food. General Characteristics The fungi constitute a group of living organisms devoid of chlorophyll. They resemble green plants in that, with few exceptions, they have definite cell walls, they are usually non-motile, although they may have motile reproductive cells, and they reproduce by means of spores. Fungi are usually filamentous and multicellular. The filaments constituting the body of a fungus elongate by apical growth. Reproductive structures are differentiated from somatic structures and exhibit a variety of forms, on the basis of which fungi are classified. 1. Nutrition andgrowth Fungi obtain their food either by infecting living organisms as parasites (Gr. Parasitos- eating beside another), or by attacking dead organic matter as Saprobes (Gr. sapros- rotten, bios- life). Fungi which live on dead matter and are incapable of infecting living organisms are called obligate saprobes. Those fungi capable of causing diseases or of living on dead organic matter, according to circumstances, facultative parasites (or facultative saprobes), and those which cannot live except on living protoplasm are called obligate parasites. Some fungal hyphae show a widespread association with the roots of higher plants and this association is known as mycorrhiza (Gr. mykes- mushroom + rhiza- root). In these associations both plant and fungus derive the benefit. Fungi differ from most plants in that they require already elaborated food in 2

3 order to live, and are incapable of manufacturing their own. But if given carbohydrates in some form preferably glucose, sucrose or maltose most fungi can synthesize their own proteins by utilizing inorganic or organic sources of nitrogen and various mineral elements essential for their growth. Many fungi are capable of synthesizing vitamins they require for their growth and reproduction. Some, however are deficient in thiamine or biotin or both and must obtain these or their precursors from the substratum. Fungi usually store excess food in the form of glycogen and oil. Most fungi will grow between 0 0 and 35 0 C but optimum temperatures lie in the range of C. The ability of fungi to withstand extremely low temperatures (as low as C) for at least a few hours has been demonstrated. They prefer an acid medium for growth, a ph of 6 being near the optimum for most of the species. Although light is not required for the growth of fungi, some light is essential for sporulation in many species. Light also plays a part in spore dispersal, the spore bearing organs being positively phototrophic and discharging their spores towards the light. 2. Somatic Structures The vegetative structure of fungi not differentiated into shoot and root is referred to as thallus. It consists of microscopic tubular filaments called hyphae (sing: hypha), Mass of hyphae constituting the thallus is called mycelium (plural: mycelia). The hyphae are branched (rarely unbranched), and the branches ramify on or inside the substratum to form a three dimensional network. Cytoplasmic streaming in fungal hyphae is unidirectional towards the tip, where growth takes place. The hyphae may be septate or unseptate (Fig. 1). The unseptate hyphae have nuclei scattered in the cytoplasm. This is known as coenocytic condition. Depending on the species, the protoplasm may be continuous throughout or it may be interrupted at irregular intervals by partitions or crosswalls, which divide the hypha into cells. The crosswalls are called septa (sing: septum; septum meaning hedge, partition). In septate forms, the protoplasts on each side of a septum are connected by living strands, which pass through a central pore in the septum. Even in the aseptate hyphae septa are formed to cut off old, empty portions of hyphae in the older region and to delimit the sex organs in the concentration of cytoplasm and are called adventitious septa. Fungi have eukaryotic cell structure (Fig. 2). They have double-membrane bound cell organelles like nucleus and mitochondria, tubular endoplasmic reticulum (ER), the golgi bodies and the ribosomes. However, there are some differences from typical eukaryotic cells, like the ribosomes, lying free in the cytoplasm and not attached to endoplasmic reticulum. Though hypha is the characteristic unit of structure in fungi, there are fungi whose thallus may consist of a single cell. Some fungi show dimorphism and exist in both mycelial and unicellular forms in different environments. Fungi possess organized, demonstrable nuclei each with a nuclear membrane, a nucleolus, and chromatin strands, which become organized into chromosomes during division. The chemical composition of the cell wall is not the same in all fungi. In most fungi, particularly in the higher forms the cell wall is composed chiefly of chitin. In some forms cellulose is probably the chief constituent. Callose, a complex carbohydrate, lignin like substances and other organic materials have also been detected in many fungi. The mass of hyphae constituting the thallus of a fungus is called the mycelium. The mycelium of some of the higher fungi forms thick strands. These strands loose their individuality and form complex tissues, 3

4 which exhibit a division of labour. These are called rhizomorphs and are resistant to adverse conditions and remain dormant until favorable conditions return. The mycelium of parasitic fungi grows on the surface of or more often inside, the host either spreading between the cells or penetrating into them. Intercellular hyphae of many fungi, especially of obligate parasites of plants, obtain nourishment through haustoria (sing: haustorium, Latin: haustor = drinker). They are regarded as specialised absorbing organs. Haustoria may be knob like in shape, elongate or branched like a miniature root system. The hyphae of saprobic fungi come in intimate contact with the substratum and obtain food by dirrect diffusion through the hyphal walls, causing disintegration of the organic matter which they utilize. The mycelium of most of fungi becomes organized into loosely or compactly woven tissues known as plectenchyma (Greek: pleko = I weave + enchyma = infusion i.e a woven tissue). There are two general types of Plectenchyma (Fig. 3). i. Prosenchyma: (Greek: pros = toward + enchyma = infusion i.e approaching a tissue). It is a rather loosely woven tissue in which the component hyphae lie more or less parallel to one another. ii. Pseudoparenchyma: (Greek: pseudo = false + parenchyma = a type of plant tissue). It consists of closely packed more or less isodiametric or oval cells resembling the parenchyma cells of higher plants. Prosenchyma and Psuedoparenchyma compose various types of somatic and reproductive structures which many fungi form. Two such somatic structures are the stroma (plural: stromata: Greek: stroma = mattress) and the sclerotium (plural: sclerotia ; Greek. skleros = hard). A stroma is a compact, somatic structure much like a mattress, on which or in which frutifications are usually formed. A sclerotium is a hard resting body resistant to unfavorable conditions, it may remain dormant for long periods of time and germinate upon the return of favorable conditions. 4

5 3. Life Cycles Many fungi, like other sexually reproducing organisms show an alternation between haploid and diploid nuclear phases in their life cycles. The haploid phase begins with the completion of meiosis and the diploid phase starts with the fusion of the haploid nuclei during sexual reproduction. In many higher Asco and Basidiomycotina a third phase the dikaryophase, intervenes the haploid and diploid phases. The nuclei associate in pairs to form dikaryons which divide simultaneously and the daughter pairs of nuclei form new cells. This multiplication of the gametic nuclei after karyogamy, results in the formation of numerous diploid nuclei. 5

6 A life cycle involving dikaryons is found only in fungi and nowhere else. Fungi display different types of life cycles centred around the sexual reproduction. Seven basic types of life cycles in fungi are generally recognised. These are: 1. Asexual cycle: the entire group of fungi imperfecti shows this type of life cycle. There is no alternation of haploid and diploid nuclear phases. The diploid (2n) phase is lacking. 2. Haploid cycle: The life cycle is completely haploid (n), the diploid phase is restricted only to the zygote nucleus. This is the most common type of life cycle found in majority of lower fungi and Ascomycotina. 3. Hapliod cycle with restricted dikaryon: This type of life cycle is found in higher Ascomycotina forming (n + n) ascogenous hyphae, which are completely dependent on the haploid mycelium. This is predominantly a haploid life cycle but it differs in the separation of plasmogamy from karyogamy in space and time. The gametic nuclei pair to form dikaryons which multiply by conjugate mitotic divisions in the ascogenous hyphae. The dikaryons finally undergo karyogamy and meiosis in the ascal primordia. 4. Haploid dikaryotic cycle: Most of the Basidiomycotina, excluding the smuts, exhibit this type of life cycle in which the dikaryophase (n + n) is more extensive and also independent of the haploid phase. The cycle comprises of two roughly equivalent phases and terminates in a single diploid nuclear generation represented by the diploid zygote nucleus. 5. Dikaryotic cycle: The complete life cycle is passed in dikaryotic phase, and both the haploid and diploid generations are represented by single nuclear generation. The immediate products of meiosis like the ascospores or the basidiospores fuse to initiate the dikaryophase, which persists until karyogamy occurs. Examples are the rusts and smuts. 6. Haploid diploid cycle: This type of life cycle, which is characteristic of algae, occurs only in two groups of fungi like the Blastocladiales and Endomycetales (Ascocybe grovesii) and Saccharomyces cerevisiae. In this type, haploid and diploid phases are equally extensive and important. 7. Diploid cycle: This type of life cycle, that is completely diploid except for the immediate products of meiosis, is reported in a number of yeasts, Myxomycetes, Blastocladiales and the Oomycetes. 4. Reproduction: Reproduction is the formation of new individuals having all the characteristics typical of the species. Two general types of reproduction are recognized, Asexual and Sexual Asexual reproduction, sometimes called somatic or vegetative, does not involve the union of nuclei, sex cells or sex organs. The union of two nuclei on the other hand characterizes sexual reproduction. In the formation of reproductive organs, either sexual or asexual, the entire thallus may be converted into one or more reproductive structures, so that somatic and reproductive phases do not occur together in the same individual. Fungi, which follow this pattern, are called holocarpic (Greek. holos = whole + karpos = fruit). In the majority of fungi, however, the reproductive organs arise from but a portion of the thallus, while the remainder continues its normal somatic activities. The fungi in this category are called eucarpic (Greek. eu = good + karpos = fruit). The holocarpic forms are, therefore less differentiated than the eucarpic and are regarded, for the most part, as more primitive. 6

7 Asexual reproduction: It is the non sexual production of specialized reproductive cells such as spores. A broader definition, however, also includes any method of propagation of new individuals, such as simple division of a unicellular organism into two daughter cells or of a multicellular thallus into a number of fragments each of which grows into a new individual. Fungi exhibit the following methods of asexual reproduction. 1. Fragmentation: A detached fragment of the hypha, in suitable conditions, gives rise to a new individual. This happens frequently in nature. 2. Budding: Budding of vegetative cells is common in yeasts (fig. 4). A soft zone appears on the cell wall, which bulges out, constricts and finally pinches off to form a daughter cell. 3. Fission: This is characteristic of bacteria and occurs only in fission yeasts Schizosaccharomyces. In fission, the cell divides in transverse plane into two cells (by constriction and later formation of a cell wall in between). 4. Spores: Spores are the most common method of asexual reproduction in fungi. The term spores is used for any small propagative, reproductive or survival unit which separates from a hypha or a sporogenous cell and gives rise to a new individual. In contrast to the vegetative mycelium, the spore is characterized by : i. cessation of cytoplasmic movement ii. iii. small water content slow metabolism and lack of vacuoles. Asexual spores are also called Mitospores. They are of two main types: Sporangiospores and Conidia (Fig. 5). i. Sporangiospores: These are formed within a sac like structure called sporangium (Pl. sporangia) which is borne on undifferentiated or specialized hyphal structure called sporangiophore. They may be motile or non-motile. The motile sporangiospores are called zoospores and are provided with one or two flagella, the nonmotile sporangiospores are called aplanospores, and they lack flagella (fig.5). Zoospores are naked spores lacking cell wall, which after a swarming period, encyst, i.e. secrete a wall, and germinate to form a germ tube that develops into the thallus. Flagella The flagella are of two types. i. Tinsel type ii. Whiplash type 7

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9 The tinsel type flagella have a whip having a broader and rigid basal portion and a thinner, small, flexible distal region. The flagella originate from kernal like granule called blepharoplast, lying in the cytoplasm close to the plasmamembrane. The blepharoplast is connected to the nucleus by a strand called rhizoplast. A cross-section of the shaft of the flagellum shows in electron microphotographs, a structure (fig.6) which is a characteristic feature of a flagella of all eukaryotic organisms. The flagellum is composed of eleven fibres, 2 central fibres covered by a central sheath and a separate outer fibre couplets in the peripheral region. A membrane surrounds the eleven fibres. Between the outer and central fibres is composed of 2 sub fibres. Each of 9 outer fibres is composed of 2 sub fibres. One of the sub fibres of each outer fibre bears two short projections, designated as arms, which point in the clockwise direction. The two central fibres are connected to the blepharoplast. The membrane surrounding the fibres is continuous with the plasmamembrane of the spore. Uniflagellate zoospore with a posterior whiplash flagellum. Uniflagellate zoospore with an anterior tinsel type flagellum. Biflagellate zoospore with one flagellum of each type attached apically or laterally. Biflagellate zoospore with two anterior whiplash flagella. These four types of zoospores form the basis of division of sub division Mastigomycotina into four classes. ii. Conidia : They are formed by transformation of pre- existing cells of the thallus and are detached by decay of the hypha, or disarticulation of the cells. a. Arthrospores: (sing: oidia) are formed by close septation of the distal end of the hypha, in a basipetalous succession (proceeding from the apex to the base of the hypha). Both exogenous and endogenous arthrospores are known (fig. 8). The exogenous arthrospores separate by splitting of the transverse septa. In endogenous formation of arthrospores transverse septa are laid down as in the exogenous arthrospores and neighbouring or alternate cells develop a thin wall. The intermediate cell lose their contents entirely and the thin lateral walls break to free the arthrospores. Small pieces of hyphal remnants remain attached at both ends of the arthrospores. b. Chlamydospores: They are thick walled, resistant spores formed by terminal or intercalary cells of the hypha and are released after death of hyphae. In the formation of chlamydospores the cells round off, usually enlarge and develop a thick, often coloured wall. The cytoplasm becomes dense with enough reserve food for consumption during unfavorable environment. Chlamydospores are resistant to lysis by chemicals produced by other soil organisms. c. Conidiospores: These are formed as new structures on the thallus and are easily detachable. They are true conidia and are most common in Ascomycotina and fungi imperfectii. Conidia may be unicellular or multicellular, display varied shapes and colour. The conidiophores may be free or aggregated to form compound sporophores like synnemata (sing: synnema) or sporodochia (sing: sporodochium). The conidiophores of a large number of fungi are borne inside structures called fruiting bodies, which may be saucer shaped acervuli (sing: acervulus). Pycnidium : (sing : pycnidium) is an ostiolate, spherical or flask shaped fruit body whose innerwall is lined with short conidiophores. Sexual reproduction: Sexual reproduction involves three principle events Plasmogamy, Karyogamy and Meiosis, occurring in a cyclic manner. Plasmogamy is the fusion of two sex cells a process that results in coming together of compatible sexually differentiated nuclei in a single protoplast in preparation for nuclear fusion. Karyogamy (fusion of nuclei) results in the production of a diploid zygote nucleus. Meiosis promotes genetic recombination through random assortment of chromosomes or crossing over, resulting in the production of genetically different individuals. 9

10 The sexual cycle of different fungi may vary due to variations in timings of the above events. In many Ascomycotina and most Basidiomycotina the plasmogamy and karyogamy are separated in space and time. The compatible nuclei do not undergo karyogamy immediately after plasmogamy but remain paired and called a dikaryon. Sex organs of fungi are called gametangia, these form the sex cells the male and the female gametes. The male gametangia is called the antheridium and female, the oogonium. The motile male gamete is called antherozoid and the female gametes, contained inside the oogonium as a differentiated nucleated mass, the egg or oosphere. Morphologically similar gametangia and gametes are called isogametangia and isogametes respectively. 10

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13 Plasmogamy: There are five basic modes of union of sexual elements. These modes of sexual fusions are often referred to as methods of sexual reproduction. 1. Planogametic copulation: This involves the fusion of two naked, free gametes, one or both of which may be motile. The motile gametes are called planogametes. Depending on size and motility of the fusing gametes, there are three types of planogametic copulation. (Fig. 10) i. Isogamy: When the two fusing gametes are of the same shape and size, they are called isogametes and their fusion isogamy. ii. iii. Anisogamy: This occurs only in one genus Allomyces a chytrid, the two planogametes are morphologically similar but different in size. Heterogamy: It involves the fusion of a motile male gamete with a non motile female gamete (oosphere, contained in an oogonium) the motile gamete, the antherozoid, enters the oogonium and fertilizes the egg or oosphere. Heterogamy occurs only in one genus Monoblepharis. 2. Gametangial contact: In this type of plasmogamy the male gamete is usually represented by the nucleus contained inside the antheridium, while the female gametes is represented by the egg contained in the oogonium (Fig.11). When the two gametangia come in contact, the male gametic nucleus (or nuclei) migrates into the oogonium either through a pore dissolved at the point of contact or through a fertilization tube, especially developed for the purpose by the male gametangium. The two gametangia do not fuse and retain their identity. The oogonium undergoes post copulation changes while the antheridium usually disintegrates. Examples: Pythium, Albugo, Phytophthora etc. 3. Gametangial copulation: The entire contents of the two gametangia fuse and become one (Fig.12). It occurs in two ways a. Direct fusion of gametangia: the two gametangia fuse and become one cell. Eg. Mucor. b. Migration of the entire protoplast of one gametangium into other through a pore. The entire gametangia act as gametes. The recipient gametangium is called the female, while the gametangium that empties its contents is the antheridium. Eg. Rhizophidium. c. Spermatization: In this minute conidia like male gametes, called spermatia (sing: spermatium) are produced on spermatiophores borne externally on hyphae or inside cavities called spermogonia (sing: spermogonium) (Fig.13). On contact with the female organ the spermatia empty their contents through a pore. The female organ may be a female gametangium a specialized receptive hypha or even a somatic hypha. The spermatia are carried to the female organ through wind, water, insects etc. the spermatia differ from conidia in being smaller. d. Somatogamy: Fusion between undifferentiated vegetative cells or spores is called somatic copulation or somatogamy (Fig.14). In mycelial forms anastomosis (fusion between vegetative hyphae), a phenomenon common in higher fungi but absent in lower fungi is followed by reciprocal nuclear migration, each mate fertilizing the other. 13

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16 Karyogamy: After plasmogamy, the two compatible nuclei may undergo fusion (Karyogamy) immediately to give rise to a diploid (2n) nucleus or may start a dikaryotic (n + n) association (Dikaryophase) extending for varying periods in different fungi. Meiosis: The diploid nucleus in the zygote may undergo meiosis immediately or after an interval. In many lower fungi the diploid zygote undergoes a resting period for varying duration and therefore called the resting spore. In such fungi sexual reproduction takes place when conditions become unfavorable for growth. The resting spores serve for survival. On the return of favourable conditions the resting spores germinate indirectly forming zoospores or directly, through a germ tube. Meiosis occurs during the germination. The meiosis in Asco and Basidiomycotina occurs in charateristic structures the asci and the basidia. The products of meiosis are the meiospores like ascospores and basidiospores which on germination give rise to the haploid mycelium. Heterothallism and Homothallism: Heterothallism is a condition in which the fungi, require another isolate for zygospore formation. The two isolates or mating types are designated as (+) and (-) strains, as their gametangia are morphologically similar and indistinguishable into male and female individuals. The opposite condition in which an individual originating from a single asexual spore, is capable of forming zygospore independently is called Homothallism. In heterothallism the two mating partners are derived from two genetically unlike spores, designated as (+) and (-) spores. Homothallic species are more common than heterothallic in all groups of fungi, except in Basidiomycotina. Parasexual Cycle: An alternative method to sexual reproduction was discovered in fungi (Aspergillus nidulans) by Pontecorvo and Roper as early as This they named as the parasexual cycle. In this process the genetic recombination is achieved through mitotic crossingover and haploidization. It is also called as somatic recombination. In A. nidulans, the parasexual cycle occurs in addition to normal sexual reproduction. While the events of sexual reproduction are extremely uniform, having a fine coordination between recombination, seggregation and reduction, there is no such coordination in the parasexual cycle. The karyogamy and haplodization are accidental events not bound by space and time. The phenomenon is reported in several fungi belonging to Ascomycotina, Basidiomycotina and Deuteromycotina. There are strong evidences of its occurrence in some coenocytic fungi, like Phytophthora cactorum. Classification: Earlier fungi were placed under division Thallophyta of the sub kingdom Cryptogamia of the kingdom Plantae. Fitzpatrick (1930) divided the thallophyta into sub-divisions Myxothallophyta (including Myxomycetes) and Euthallophyta (which included lichens, bacteria, algae and fungi). 16

17 This is detailed below Kingdom: Plantae Sub kingdom: Cryptogamia Division: Thallophyta Subdivision 1: Myxothallophyta Subdivision 2: Euthallophyta Once bacteria, lichens and myxomycetes were included among fungi. Though bacteria were promptly removed from fungi, the Myxomycetes continued their inclusion among fungi. These are studied by mycologists by tradition and preserved along with collections of fungi. Nonetheless, they have always been kept separated from the true bonafide fungi, the Eumycetes. Tippo (1942) removed the division thallophyta because of its heterogenity. In a very early attempt to classify fungi, the true fungi were divided by Saccardo (1866) into four classes- Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes, on the basis of presence or absence of septa and characteristics, sexually produced spores. (viz. Oospores, zygospores, ascospores and basidiospores). Fungi Thallus or mycelium aseptate Mycelium septate Phycomycetes Characteristic spores - Endogenous, Ascospores Characteristic spores Exogenous, Basidiospores Ascospores and Basidiospores lacking lacking, possess asexual spores only Ascomycetes Basidiomycetes Dueteromycetes The Phycomycetes are also sometimes loosely called as lower fungi and the fungi belonging to Asco-, Basidio-, and Deuteromycetes as the higher fungi. 17

18 The four class classification of fungi dominated mycology for a long time. However, it was felt that the sub class Oomycetes was an assemblage of unrelated forms. In 1943, F. K. Sparrow emphasized that on the basis of flagellation of the zoospores, the aquatic phycomycetes (erstwhile subclass Oomycetes of class Phycomycetes) could be separated into two series uniflagellate and biflagellate. Sparrow emphasized that flagellation was a good taxonomic and phylogenetic criterion. The classes are: o o o o Chytridiomycetes, Hyphochytridiomycetes, Oomycetes and Plasmodiophoromycetes. The other sub class Zygomycetes of the class Phycomycetes was also given class rank. A group of Phycomycetes which are internal parasites of arthropods was also elevated to class rank. This resulted in nine classes of fungi : 1. Chytridiomycetes 2. Hyphochytridiomycetes 3. Plasmodiophoromycetes 4. Oomycetes 5. Zygomycetes 6. Trichomycetes 7. Ascomycetes 8. Basidiomycetes 9. Deuteromycetes (fungi imperfectii). Alexopoulos (1962) u sed this nine class classification in his book, the immense popularity of which made this classification widely accepted. Alexopoulos named this division as Mycota and separated Myxomycetes and true fungi under two sub divisions The Myxomycotina and Eumycotina, respectively. The next important change ca me in 1966, when G.C. Ainsworth proposed a classification of fungi which has been used in the Dictionary of fungi and also followed in The Fungi, An Advanced Treatise Vol VI (1973). Fungi are treated in this classification as a separate kingdom but those unable to reconcile with this complete separation of fungi from plants, can continue considering them as a sub kingdom of Plantae. Further Hawksworth et al. in 1995 used this as the basis for classifying fungi. The kingdom of fungi is divided into two divisions: The Myxomycota, for plasmodial forms and Eumycota (True fungi), for non-plasmodial forms, which are usually mycelial. The true fungi are divided into five sub divisions viz. Mastogomycotina, Zygomycotina, Ascomycotina, Basidiomycotina and Deuteromycotina. The outline of the classification of Ainsworth widely accepted currently is given below. 18

19 KINGDOM MYCOTA (Fungal Kingdom) 1 Division: MYXOMYCOTA - (4 Classes) i. Acrasiomycetes ii. Hydromyxomycetes iii. Myxomycetes iv. Plasmodiophoromycetes II Division: EUMYCOTA - (5 Sub divisions) a. MASTIGOMYCOTINA- (4 classes) i. Chytridiomycetes ii. Hyphochytridiomycetes iii. Plasmodiophoromycetes iv. Oomycetes b. c. d. ZYGOMYCOTINA - (2 classes) i. Zygomycetes ii. Trichomycetes ASCOMYCOTINA - (6 classes) i. Hemiascomycetes ii. Laculoascomycetes iii. Plectomycetes iv. Laboulbeniomycetes v. Pyrenomycetes vi. Discomycetes BASIDIOMYCOTINA - (3 classes) i. Teliomycetes ii. Hymenomycetes iii. Gasteromycetes e. DEUTEROMYCOTINA - (3 classes) i. Blastomycetes ii. Hyphomycetes iii. Coelomycetes 19

20 Recently Alexopoulos et al. in 2002 classified fungi into three different groups as, the monophyletic kingdoms 1.Fungi and 2.Stramenopila and 3.four Protist phyla. 1 Kingdom Fungi 2 Kingdom Stramenopila Phylum Chitridiomycota Phylum Zygomycota Phylum Ascomycota Phylum Basidiomycota 3 Protists Phylum Oomycota Phylum Hyphochytriomycota Phylum Labyrinthulomycota Phylum Plasmodiophoromycota Phylum Dictyosteliomycota Phylum Acrasiomycota Phylum Myxomycota This classification which is slightly c omplicated will be more useful to research scientists and at post graduate level. In this book the most widely used classification of fungi by Hawksworth et al. (1995) is followed. Division : Myxomycota Class : Acrasiomycetes (Cellular slime molds) The acrasiomycetes are called cellular slime molds to distinguish them from the true slime molds, which form plasmodia. They form curious well form ed fruiting bodies by a large number of cooperating individual cells (amoebae) and are called as social amoebae. The Acrasiomycetes comprise about two dozen species which are free living soil inhabitants. The most extensively studied are Dictyostelium mucoroides and D. discoideum. These are usually isolated from humus containing soils. Life cycle : The basic units of Acrasiomycetes are naked, uninucleated, haploid amoebae. They move over solid media by means of pseudopodia, feed by phagocytosis of bacteria and multiply (Fig. 15). Eventually, the amoebae migrate towards an aggregation centre and form an aggregation plasmodium, which is called a pseudoplasmodium to distinguish it from the multinucleate, but unicellular true plasmodium of the myxomycetes. Although the individual amoebae maintain their identity the pseudoplasmodium functions as a unit. It forms a slug. A cap is formed in which the axis of the fruiting body, the sorophore becomes differentiated. The cells on the upper surface form a stem, which is enclosed in a cellulose coat, whilst the cells from the posterior or lower part migrate to the apex of the stem where they form a spherical head, the sorocarp, and develop into spores. The spores are encysted amoebae. On germination of a spore, a pore appears in the cellulose coat through which the amoeba is liberated to begin a new cycle. 20

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22 Class : Myxomycetes (True slime molds). The myxomycetes form fruiting bodies that are very similar to those of the myxobacteria and of the Acrasiomycetes, although they are larger than either of these. The developmental cycle is shown in (Fig. 16). Myxomycetes occur in damp places in wood, on fallen leaves, bark, timber and old fence posts. They are sometimes conspicuously colored fruiting bodies, about cm in size and are easily visible. Some of the representatives are Lycogala epidendron, Cribaria rufa, Fuligo septica etc. 22

23 Life cycle The spores liberated from fruiting bodies germinate on moist surfaces and produce flagellated swarmers or myxamoebae. These feed on liquid nutrients or by phagocytosis of bacteria, yeasts, fungal spores etc. The myxoflagellates lose their flagella after a time and enter an amoeboid stage. These cells are mononucleate. Eventually, they fuse in pairs (plasmogamy and karyogamy) to become myxozygotes. These diploid amoeba remain as such or fuse with other amoebae to form the plasmodia, which are then multinucleate. Under favorable nutritional conditions, the number of nuclei increases by repeated mitotic divisions. The plasmodia are negatively phototaxic (ie., light avoiding) and achieve a favourable situation by means of hydrotaxis and chemotoxis. The plasmodia give rise to the fruiting bodies or sporangia. The plasmodia leave their dark and moist locations and migrate towards the light. It undergoes reduction division or (meiosis) followed by formation of a more or less complicated sporangium which has a firm envelop on its outer surface (the peridium). Numerous small, membrane enveloped, mononucleate spores arise in its interior. The residues that remain between the spores form a network or skeleton, which is called the capillitium. On maturation and opening of the peridium, the spores are blown out of the sporangium by air currents. Subdivision : Mastigomycotina Division : EUMYCOTA Fungi which produce motile zoospores are placed under the subdivision Mastigomycotina. The zoospores are uniflagellate or biflagellate. The flagellum may be of whiplash or tinsel type. The anterior or posterior position of the flagella may be known by their orientation during locomotion. A characteristic feature of the biflagellate spores is that during movement, the flagella are always oppositely directed. On the basis of number (one or two), position, (anterior, posterior or lateral) and type (whiplash or tinsel) of the flagella on the zoospores, the subdivision Mastigomycotina is divided into four classes : 1.Chytridiomycetes 2.Hypochytridiomycetes 3.Plasmodiophoromycetes 4.Oomycetes Key to classes of Mastigomycotina I. Zoospores uniflagellate (monoplanetic) a. Flagellum posterior, whiplash type - Chytridiomycetes b. Flagellum anterior, tinsel type - Hyphochytridiomycetes II. Zoospores biflagellate (diplanetic) a. Flagella unequal, both of whiplash type, thallus plasmodial plasmodiophoromycetes 23

24 b..flagellum rarely equal, anterior flagellum tinsel type, posterior flagellum whiplash, cell wall cellulosic - Oomycetes. According to Klein and Cronquist (1967) the plasmodiophoromycetes are more allied to Myxomycetes. Ainsworth (1966, 1973) included the plasmodiophoromycetes in division Myxomycota. Nonetheless, this class has been dealt with under sub division Mastigomycotina by Waterhouse (1973) in The Fungi, An Advanced Treatise Vol. IV B. Class : Oomycetes General characteristics They range form unicellular, holocarpic, endobiotic parasites of aquatic algae and fungi to forms having well developed mycelium The most advanced peronosporales include obligate parasites of plants viz., the downy mildews and the white rusts which pass their entire life cycle on living host tissues. They produce laterally biflagellate, reniform zoospores. The two flagella, which are laterally attached, are dissimilar in structure and size. One is tinsel and the other is of whiplash type They contain cellulose in their cell wall They show oogamous type of sexual reproduction usually involving a club shaped antheridium and globose oogonium containing one or more non mobile female gametes called oosphere or egg. The male gametes fuse with female gamete or egg resulting in thick walled zygote called oospore. Classification The class Oomycetes has been divided by Sparrow (1973) into four orders, on the basis of whether (i). The zoospores are formed in the zoosporangium proper or in vesicle, formed by the zoosporangium and (ii). The holocarpic or eucarpic nature of the thallus. Key to orders of Oomycetes I. Zoospores invariably formed in the sporangium diplanetic, monoplanetic or aplanetic (a) Holocapric or eucarpic, hyphae when present lack constrictions Saprolegniales (b) Eucarp ic hyphae with constrictions Leptomitales II. Zoospores formed within the sporangium or a sporangial vesicle ; monoplanetic and reniform (a) Holocarpic - Lagenidiales (b) Encarpic - Peronosporales The Lagenidiales are the most primitive among the Oomycetes, while the Peronosporales are the most advanced. Order : Peronosporales General characteristics : - They are more suited to amphibious or terrestrial habitat. - They form sporangia in dry weather instead of forming zoospores 24

25 - The intercellular hyphae of parasitic genera form haustoria which enter host cells and absorb nutrients The order is divided into three families on the characteristics of sporangiophore and sporangia 1) Pythiaceae 2) Albuginaceae 3) Peronosporaceae Family : Pythiaceae The family includes aquatic, amphibious or terrestrial fungi, many of which are important parasites of plants viz., Pythium and Phytophthora. Genus : Pythium This is the largest genus of the family. Majority of them are soil inhabitants which mainly cause root-rot and damping off diseases of seedlings. Some are aquatic some amphibious and some terrestrial. Some attack fruits (prominent being the cucurbit fruits lying usually on the ground). The mycelium is well developed; haustoria are produced in some species. The hyphae which bear the sporangia are indistinguishable from the mycelium in most species. In some species, however definite sporangiophores are formed. Life cycle of Pythium debaryanum The fungus grows saprophytically in soil, as well as, parasitically in host tissues. The hyphae grow inter or in tracellularly in the host ti ssues. Haustoria a re not produced. Globose or ova l sporangia arise apically on unspecialized hyphae (Fig. 17). 25

26 26

27 At the time of zoospore formation, a discharge tube with an apical vesicle appears on the sporangium into which the contents of the latter migrate and gets converted to zoospores. The mature zoospores show a rocking motion and bounce on the delicate wall, causing its rupture and consequent release of the zoospores. The discharge tube often persists after the dehiscence of the vesicle. The zoospores (reniform, laterally biflagellate), after the swimming period, encyst and germinate by forming a germ tube which grows into a hypha. In dry weather, the zoosporangia behave as conidia and germinate directly by forming a germ tube. Sexual Reproduction The gametangia, which are formed on same and different hyphae, may be terminal or intercalary. The oogonia are globose, periplasmatic, with a single oosphere and have a colourless, smooth or spiny wall. The antheridia are club shaped and smaller, may be hypo (below) or paragynous (side) in position. At maturity, the gametangia are uninucleate. Plasmogamy takes place by gametangial content. The male nucleus is transferred to the female counterpart in the oosphere by forming a fertilization tube. This is followed by karyogamy immediately or a little before oospore germination. The oospore is usually colourless, unornamented. It undergoes a period of rest before germination and divides by meiosis to form zoospores which later germinate to give rise to new thalli. Economic Importance 1. Many species of Pythium are plant pathogenic and known to cause various diseases like Pythium debaryanum causing damping off of tobacco and chillies. Pythium aphanidermatum causes soft rot of papaya and damping off of potato P. graminicolum causes rhizome root rot of turmeric and P. myriotylum causes foot rot of ginger. Genus : Phytophthora The chief distinction between the genera Pythium and Phytophthora is the method of sporangia germination. In general, no vesicle is formed in Phytophthora or, if one is formed, the zoospores differentiate in the sporangium proper and pass into the vesicle as mature zoospores. They are liberated by the bursting of the vesicular wall. Most the members are parasitic and few are saprophytic. Many, which have been isolated from soil, attack under ground plant parts but there is little evidence that they can grow and reproduce in soil. Many species attack aerial parts of plants and cause fruit rot, canker and leaf blight diseases. Late blight of potato caused by P. infestens is an important plant disease. 27

28 Life cycle of Phytophthora infestens The fungus survives in potato tubers in form of dormant mycelium and when such tubers are used as seeds they give rise to systemically infected plants. The hyphae grow intercellularly in host tissues and form haustoria to derive nutrition from adjacent cells and the optimum temperature for growth is 20 0 C (Fig. 18). Asexual Reproduction This is brought about by zoospores. Sporangial production needs a low temperature ( C) and high relative humidity (91-100%). The sporangiophores emerge form the lower surface of leaves through stomata and bear terminal, lemon shaped sporangia with distinct papilla. The sporangiophores also arise in large numbers from the cut surfaces of infected, stored potatoes. The sporangia are deciduous and got widely disseminated through wind or soil water. The sporangia germinate directly or form zoospores. The reniform, biflagellate zoospores, as usual swim for sometime, then encyst and finally germinate to form a new hypha. The tip of the germ tube, on host leaf surface, forms an appresorium (a bulbous apical swelling) from which an infection hypha enters the host and establishes an intercellular mycelium. Dead, blighted areas appear on the leaves and indicate infection. Zoospores present in the soil infect the tubers. Sexual Reproduction It is infrequent in P. infestans for the reason that it is heterothallic and the + and strains are not reported. If present the young oogonium grows through the antheriduum and after emerging above develops into the mature globose structure. The antheridium forms a funnel or collar shaped structure at the base of the oogonium. The oogonium, which is initially multinucleate at maturity contains a single nucleus. The protoplasm at the centre of the oogonium is called ooplasm which contains the female nucleus and serves as the female gamete called egg or oosphere. The cytoplasm surrounding the ooplasm is called periplasm. The club shaped antheridium, which too is initially multinucleate, finally contains a single male nucleus. The male nucleus reaches the oosphere through a fertilization tube formed by the antheridium. Plasmogamy, followed by karyogamy, results in a diploid zygote nucleus or oospore. After a rest period the oosphere germinates and forms a zoosporangium at the tip of the germ tube. Zoospores of the two mating types are formed in equal number, which give rise to thalli of opposite mating type s. 28

29 29

30 Economic importance Most of the species are parasitic and some are saprophytic. They are known to cause various diseases in some of the important crop plants like a. Phytophthora infestans causes late blight of potato b. P. colocasiae causes late blight of colacasia c. P. parasitica var sesami causes leaf blight of sesamum d. P. palmivora causes bud rot of toddy palm, coconut etc e. P. nicotianae causes black shank of tobacco etc. f. Sub division : ZYGOMYCOTINA The sub division Zygomycotina includes coenocytic fungi which lack motile cells and produce zygospores as the perfect or sexual spores. The zygospore typically results from the complete fusion of the two gametangia during gametangial copulation. These reproduce asexually by means of aplanospores, (also called sporangiospores formed inside sporangia) or conidia. The sub division Zygomycotina consists of two classes : 1. Zygomycetes 2. Trichomycetes Key to classes of Zygomycotina 1. Saprobic or if parasitic or predatious, having mycelium immersed in host tissues Zygomycetes 2. Associated with arthropods and attached to the cuticle or digestive tract by a hold fast and not immersed in host tissue Trichomycetes The zygomycetes are placed in three orders : (1) Mucorales (2) Entomophthorales (3) Zoopagales Order : Mucorales The fungi live on rotting organic materials, some are coprophilic, ie., they prefer excreta as substrate, hosts droppings etc. Names such as Mucor mucedo, Rhizopus nigricans (the common bread mould), R. oryzae, R. arrhizus, R. rouxii, Choanephora cucurbitarum etc. are well known not only to the mycologist, but also because of their industrial importance, to chemists and biotechnologists. Fungi generally grow only sparsely and for a limited time under anaerobic condition. On exclusion of atmospheric oxygen they can resort to fermentation, and form lactic acid or ethanol. At the same time, they adopt a new growth habit. Mucor racemosus, for example, forms a sprouting mycelium under anaerobic conditions and the newly formed cells then multiply by budding, like yeasts. 30

31 The mucors can spread rapidly, both by the rapid growth of their hyphae and by the proliferation of numerous sporangiophores. Some Rhizopus stolonifer (R. nigricans) for example, form stolons that can bridge distance of several centimeters. The order Mucorales is divided into fourteen families among them family Mucoraceae is the most primitive family from which other families are believed to have arisen. Family : Mucoraceae There are 20 genera that grow on different habitats. Some are exclusively parasitic on mushrooms like Syzygites, Dicranophora, Spinellus. Some are strictly soil fungi like Zygorrhyncus and many species of Mucor and Absidia; Pirella and some species of Mucor are coprophilous ie., dung inhabiting. Rhizopus and Absidia attack stored grains. Genus: Mucor This is a large genus of with more than 600 species. The hyphae are coarse, coenocytic and richly branched. Septa appear in older hyphae and the chlamydospores are formed between such septa, which constitute the diagnostic feature of M. racemosus. Life cycle The life cycl e includes both asexual and sexual methods of reproduction. Asexual reproduction occurs by formation of sporangia and sporangiospores (Fig.19). Vertical branches arise from the luxuriously growing mycelium, become delineated by a septum and swell at their apices into spherical heads. An outer zone, rich in cytoplasm, separates from a poor inner zone, they are separated by a cell wall and the columell a arches into the sporangium. Hundreds or even thousands of nuclei can be found in the peripheral zone, each surrounded by cytoplasm and developing into sporangiospores. Some of the mucors bear small sporangia or sporangioles on branched sporangial carriers, each sporangium containing only one or few spores. On maturity, when the sporangial wall dissolves, the spores remain firmly adhered to collumella in a drop of fluid and are not blown off even by strong winds. The spores are disseminated by insects and ants. Sexual Reproduction During the developmental cycle ( Fig.19) the liberated sporangiospores are mulinucleate. They germinate under favorable condition s and develop a highly branched aerial mycelium. Sexual reproduction occurs only when two physiologically differentiated, compatible (+ and -) mycelia come into contact. As these approach, copulation branches are formed that enlarge into progametangia and become enriched with cytoplasm and nuclei. They eventually separate from the carrier hyphae by means of septum formation. The cell walls in the contact zone of the gametangia disintegrate and the protoplasts fuse (gametangiogamy). Each (+) nucleus pairs with a (-) nucleus and nuclear fusion takes place. During this phase the coenozygote enlarges and forms a thick walled zygospore. After a resting phase, the zygospore opens and germinates into a germ sporangium in which the nuclei undergoing meiotic division and form sporangiospores which germinate to form the vegetative body. The vegetative body, therefore is haploid. Some of the mucors are homothallic and self fertile. 31

32 Economic importance Many mucorales are saprophytic Various organic acids like fumaric acid and lactic acid are manufactured from species of Rhizopus under anaerobic conditions Species of Rhizopus and Mucor are used in industrial fermentations at the initial stages for converting starch into sugar Strains of Rhizopus find use in the preparation of a delicious food Tempeh from soybeans in Indonesia. Sufu or Chinese cheese is prepared from soybean with the help of Actinomucor. Many species of Mucorales cause diseases of fruits during storage like R. stolonifer causes soft rot of sweet potatoes and leak of strawberries, raspberries, peaches etc. Some species of Rhizopus, Mucor and Absidia attack stored grains Spoilage of bread by Rhizopus is so common that one of its species (R. niger) is called the bread mold Mucorales are known to cause Mucoromycosis of domestic animals and man causing infections of lungs, brain and other organs. 32

33 Fig. 19: Life Cycle of Mucor sp

34 Sub division : ASCOMYCOTINA General characteristics - These are the fungi which possess an ascus, containing ascospores formed after karyogamy and meiosis. - They have a septate vegetative mycelium which is profusely branched - The cell wall is made of chitin - The vegetative hyphae are often organized into somatic tissues like sclerotia, stroma and mycelial strands. a) Sclerotia are firm aggregations of modified vegetative hyphae which serve as resting bodies to overcome adverse environment b) Mycelial strands are linear hyphal aggregates capable of unlimited growth in one direction c) Stromata are compact somatic structures which bear spores or the fructifications. - These fungi reproduce both asexually as well as by sexual methods a) Asexual reproduction takes place by budding, fission, fragmentation, chlamydospores and conidia of these, conidia are the most important. The conidia are borne on conidiophores which may be scattered on the mycelium or formed in special structures the fruit bodies like pycnidium, acervuli and sporodochia. Pycnidium : is an ostiolate, spherical or flask shaped fruit body whose innerwall is lined with short conidiophores. The acervules is a disc shaped, flat stromatic mass of hyphae. Sporodochium consists of a cushion shaped stroma bearing conidia externally. Sometimes conidiophores occasionally aggregate and fuse up to varying lengths to form structures called synnemata (sing. synnema) and coremia (sing coremium). In synnema the conidiophores are joined at the base and free above near the tip, while in a coremium the conidiophores are only loosely aggregated. b) Sexual reproduction is initiated by the formation of ascogonia (sing = ascogonium, the female sex organ) (Fig. 20). The ascogonia are usually globular and bear a hair like out growth called trichogyne. The trichogyne receives the male nuclei, which are thus led from the antheridium via the trichogyne into the ascogonium (plasmogamy) where the nuclei pair but do not yet fuse. The ascogonium now gives rise to the so called ascogenous hyphae, each of whose cells contains one male and one female nucleus (dikaryotic hyphae). The nuclei divide simultaneously. Fusion of the dikaryon is initiated by a specific cell division, hook formation. The hyphal apex curves in the form of a hook, the nuclear pair divides conjugatively. The upper pair of nuclei are separated by a septum both form the stem cell and form the hook. The hook then fuses with the stem cell, thus producing another dinucleate cell. The upper hook cell becomes the ascus in which the fusion of the two nuclei occurs. The resulting primary ascus nucleus then undergoes two divisions of which one is meiotic. The eight 34

35 daughter nuclei then form the eight ascospores. Sometimes the number of divisions can be smaller (four spores) or very large (> 1000 spores). Both the ascospores and the mycelium are thus haploid. With few exceptions, the asci are formed in fruiting bodies (ascocarps). These represent the envelope or the cushion in which the sexual organs reach maturity. The hyphal network gives the characteristic shape to the fruiting body. Three different forms are distinguished (Fig. 21). The completely closed fruiting body called the cleistothecium which is the characteristic of Plectomycetes a usually flask shaped fruiting body called a perithecium which is typical for the Pyrenomycetes an open, bowl shaped fruiting body called an apothecium which is typical for Discomycetes. In addition, there are some fungi that bear naked asci (protoascomycetes). In the truffles (Tuberales) the ascocarps remain closed. The ascus wall may be unitunicate or bitunicate and this is an important character in the taxonomy of Ascomycotina. The unitunicate asci have two thin walls which appear as a single wall. The bitunicate asci have an outer rigid and an inner extensible wall. The inner wall in maturity comes out of the breakage of the outer wall. The extensible inner wall has an apical pore through which the spores are forcibly ejected. In unitumicate asci, the ascospores are ejected through several ways, a pore, a slit, an operculum (lid) or by breaking of the apical wall. In a large number of Asomycotina the ascospores are released forcibly. 35

36 Classification Ascomycotina is divided into 6 classes viz. Hemiascomycetes, Laculoascomycetes, Plectomycetes, Laboulbeniomycetes, Pyrenomycetes, and Discomycetes. The primitive genera lacking ascocarp and ascogenous hyphae are segregated under class Hemiascomycetes. The rest which form ascogenous hyphae and ascocarps are further divided on the basis of the uni or bitunicate nature of th e ascus and fruit body characteristics. In Plectomycetes the asci lie at different levels in cleistothecium and are evanescent. The Pyrenomycetes have persistant and inoperculate asci borne in perithecia. In Discomycetes, the asci (operculate or inoperculate) lie in a hymenium in apothecia. In Laboulbeniomycetes are exoparasites of arthropods, which bear their asci in a hymenium in perithecia. The bitunicate asci represent a major step in the evolution of Ascomycotina and therefore, the bitunicate genera are placed separately under the class Loculoascomycetes. 36

37 Class : Hemiascomycetes Hemiascomycetes are characterized by (i) Direct development of asci from the zygote and (ii) absence of asci The thallus is represented by single cells (as in yeasts), pseudomycelium or feebly developed hyphae. The fungi included in this class are considered as most primitive among Ascomycotina. The class is divided into three orders and five families (Martin 1961, Ainsworth 1966, 1973). 1. Protomycetales - Protomycetaceae 2. Endomycetales - Spermophthoraceae - Ascoideaceae - Endomycetaceae - Saccharomycetaceae 3. Taphrinales - Taphrinaceae Order Endomycetales Zygotes or single cells develop directly into asci. In some forms the zygote gives rise to a large number of cells by budding which eventually develop into asci. The order is divided into four families, based on characters of sexual and vegetative reproduction. Key to families of Endomycetales (After Kreger-Van Rij, 1973) 1. Asci multi spored ; mycelium abundant Ascoideaceae. 2. Asci usually 1-8 spored, mycelium absent or present a) Ascospores needle or spindle shaped Spermophthoraceae b) Ascospores not needle or spindle shaped i. Mycelium usually lacking or scanty single cells reproducing by budding or fission Saccharomycetaceae ii. Mycelium abundant, no single budding cells Endomycetaceae Family : Saccharomycetaceae The family includes the ascogenous yeasts, which characteristically ferment sugars. Most of the yeasts are saprobes growing on sugar substrates like flower nectar, ripe fruits and also occur in milk, soil, animal excreta and plant parts. These fungi are of great economic importance. The family is divided into 4 subfamilies, accommodating 19 genera including important genera like Schizosaccharomyces, Saccharomyces etc. 37

38 Genus: Saccharomyces Ex. Saccharomyces cerevisiae All the species of genus cause vigorous fermentation of sugars, hence the name saccharo (sugar) myces (fungi). S. cerevisiae is called as yeast of commerce or bakers and brewers yeast because of its extensive use for production of alcohol (in brewing industry) and CO 2 to render the bread spongy (in baking industry). Yeast tablets are also used in medicine as a source of vitamin B complex. Cell structure Yeasts are oval in shape, with a wall made of chitin fibrils and having polysaccharides, manan and glucan (Fig.22). Several bud scars, which are remnants of the detached daughter bud cells, persists on the external surface of the cell wall. There is an unusually big central vacuole pushing the protoplasm to the periphery. The cytoplasm contains the usual cell organ elles like nucleus, mitochondria and reserve food granules (glycogen, oil and refractile volutin granules whic h are inorganic metaphosphate polymers). Life cyc le : Yeasts show both asexual as well as sexual methods of reproduction in their life cycle. Asexual reproduction The yeasts, usually reproduce asexually by budding and hence, commonly called as budding yeasts. But some species reproduce by fission and are called as fission yeasts. (i) Budding : It is the common method of reproduction that The process of budding is described as follows (Fig. 23): takes place under favourable conditions. The process starts by formation of a small outgrowth or bud at one pole of the cell. During the formation of a small outgrowth or bud at one pole of the cell, the nucleus divides into two and one daughter nuclei migrates into the bud. The bud increase in size and becomes constricted at the base forming a mature bud. The bud may remain with parental cell or might get pushed off from the parental cell by the growth of the constriction. Thus daughter cell is unequal in size. When the nutrient levels are sufficient th e budding process becomes so rapid that the daughter cells formed starts forming a new bud and it results in formation of a chain of buds. These chains are branched or unbranched and are called as pseudomycelium. (ii) Fission: The process of fission is exhibited by Schizosaccharomyces sp. and are known as fission yeast. The yeast cell elongates followed by karyokinesis (division of nucleus), i.e.the two daughter nuclei move towards either pole. A constriction starts developing in the middle of the yeast cell resulting in the development of two daughter cells (Fig.24). 38

39 39

40 Sexual reproduction: Sexual reproduction in yeast is not a normal type of reproduction as it occurs only during unfavorable conditions, the yeast cells do not produce any definite sex organs such as antheridia or oogonia. They reproduce by fusion of two compatible somatic cells which act as gametangia. Fusion indicates plasmogamy and karyogamy followed by meiosis. Yeasts show three different types of life cycle patterns called Haplobiontic, Diplobiontic and Haplo-diplobiontic life cycle. (1) Haplodiplobiontic life cycle: S. cerevisiae (Fig.25) shows haplo-diplobiontic type of life cycle, in which both haploid and diploid phases are equally extensive and important. Both types of vegetative cells i.e. haploid and diploid, multiply by budding and eventually transform into the other type. The haploid cells of opposite mating types after fusion (plasmogamy and karyogamy) give rise to diploid phase, the diploid nucleus undergoes meiosis and forms four haploid nuclei around which four ascospores are developed. Thus, the diploid cells are potential asci. On release after lysis of the ascus wall, these grow into vegetative cells establishing the haploid phase. 40

41 (2) Haplobiotic life cycle: This type of life cycle is seen in Schizosaccharomyces octosporus (Fig. 26). Sexual reproduction involves gamentangial copulation between two similar haploid cells. All species are homothallic under the genus Schizosaccharomyces. Each somatic cell is a potential gametangium. The two cells fuse at the tip, their nuclei migrate into the narrow isthumus or conjunction tube. Karyogamy takes place and the fused zygote cell enlarges to become the ascus. The diploid nucleus undergoes meiosis followed by mitosis and 8 haploid nuclei are produced, around which eight ascospores are elaborated. The cellwall dissolves by the autolysis liberating the ascospores, which grow into haploid cells. The life cycle being haploid and the diploid phase is very short represented only by the zygote, it is termed as haplobiontic type of life cycle. 41

42 42

43 (3) Diplobiontic life cycle: The genus Saccharomycode reproduces vegetability by both budding and fission. The ascospores conjugate while still inside the ascus. There is a single species S. ludwigii, which is diploid and heterothallic. The life cycle shows (Fig. 27) a long diploid and a short haploid phase i.e. diplobiontic life cycle. The haploid stage is represented by a single generation of ascospores. The diploid cells multiply by budding as well as fission. Each cell is a potential ascus. When conditions become unfavorable for growth and multiplication, it behaves as an ascus. The diploid nucleus undergoes meiosis and form four haploid nuclei of two mating types, which develop into four ascospores. The ascospores of the opposite mating types undergo conjugation while still inside the ascus. The zygote cells, formed within the ascus, put out a germ tube, which breaks through the ascus wall and forms a sprout mycelium from which are budded off several diploid somatic cells. 43

44 Economic Importance: Yeasts bring about fermentation of sugars producing ethanol, glycerol, acetic acid etc. Yeasts cakes are used for domestic purposes Yeasts are a source of number of vitamins and proteins Yeasts also cause spoilage of food and some are parasitic on humans and plants Class : Plectomycetes The characteristics of the members of this class is that the asci are globose or broadly club shaped, they arise at different levels in the ascocarp and are therefore, irregularly arranged, they have no natural opening but release the ascospores by deliquescing and setting them free in the ascocarp. The ascocarp either is completely closed (cleistothecium) or has an ostiole. The Plectomycetes includes three orders 1. The Eurotiales 2. The Onygenales 3. The Microascales Order: Eurotiales (Aspergillales or Plectascales) The members belonging to this order produce their cleistothecia on the mycelium without the formation of a stroma. The asci are formed from ascogenous hyphae of various length and are consequently scattered at various levels within the ascocarp. There is therefore no definite hymenial layer. The order includes several hundered species of fungi, most of which are saprobes, but some of which are parasitic on plants, animals and human beings. The conidial stages of many of these fungi are of very common occurrence and are familiar to everyone under the names of blackmold, greenmold and bluemold. The order is divided into three families 1. Ascosphaeriaceae 2. Gymnoascaceae 3. Eurotiaceae Family : Eurotiaceae The Eurotiaceae are among the most widely distributed fungi. The family includes a number of genera, most of them having well formed cleistothecia with definite peridia. There are three genera, Eurotium, Sartorya and Emericella whose conidial stages are of Aspergillus type. Chiefly because of these connections, the Eurotiaceae are of considerable importance and have been studied intensively. 44

45 Form-genus: Aspergillus There are 78 species of Aspergillus recognized. The black aspergilli or Aspergillus niger group are the fungi which are commo nly called blackmold. Conidia of Aspergillus are always present in air and cause contamination in laboratory cultures of bacteria and fungi, hence also called weed of the laboratory. Thallus: The hyphae are hyaline, septate and branched. The cells are multinucleate. Reproduction: The conidial state is dominant and the sexual stages are either absent or rarely produced. Species which have only conidial stage are called Aspergillus, while those in which sex organs are formed are placed in the genera Eurotium, Emericella and Sartorya. Asexual reproduction: The conidia are produced in enormous quantity. The mycelium starts forming conidiophores very early. The long and erect conidiophores arise from a particular thick walled foot-cell (Fig.28). It forms a terminal swollen vesicle, on which bottle shaped structures called sterigmata or phialides arise all over the surface and produce chains of conidia at their tips. When there are two layers of sterigmata the lower is called primary sterigmata or metulae and the upper, as secondary sterigmata or phialides. 45

46 The phialides are bottle shaped. The neck is called the spore producing tube, the conidia are formed inside this tube. A portion of protoplasm with a nucleus inside the neck is delimited by a septum. The protoplasm rounds off, develops a wall which fuses with the wall of the tube and becomes a conidium, and in this way conidia are produced at the tip of the philaide. The conidia remain attached in chains. The conidia are circular, multinucleate and have a thick and rough wall. The color of the conidiophores and the conidia are responsible for the color of the colony, which may be green (A. flavus), yellow (A. ochraceus), brown (A. tamari), black (A. niger),white (A. candidus) etc. the colony color is an important criterion in the identification of species. The conidia, which are dry, are easily detached and diseminated by wind. 46

47 Sexual reproduction: Some species like A. niger lack sexual reproduction. Species of Aspergillus forming sex organs are put under the genera Eurotium, Emericella and Sartorya. In this the degeneration of sex organs, especially the antheridium is common. The antheridia and ascogonia are produced closely on the same somatic hypha (Fig. 28). Both are multinucleate, helical and elongated structures, which coil around each other. Pairing of nuclei, derived from antheridia and ascogonia, occurs in the ascogonium. Ascogenous hyphae arise from the ascogonium and pairs of nuclei migrate into them. The ascogenous hyphae grow to unequal lenghts and produce asci at different levels. Simultaneously, with the development of the asci, hyphae arise from the base of the ascogonium and collect around the sex organs and form a characteristic simple astomatous (non-ostiolate) ascocarp. The pseudoparenchymatous wall of the ascocarp peridium and the asci are jointly called as cleistothecium. The cleistothecia are spherical and small ( µm) contain large number of minute 8 spored, globose asci. These dissolve leaving the ascospores free from inside the cleistothecium. The cleistothecia open by natural weathering or by rupturing ascogenous hyphae. The ascospores thus liberated, on germination, produce germ tube which give rise to the mycelium. The species groups: The species groups of Aspergillus and their perfect stages are as follows glaucas group - Eurotium nidulans group - Emericella fumigatus group - Sartorya Economic importance: The aspergilli are found to affect human welfare in a variety of ways. A. niger and several other species are often found on exposed food stuffs and cause decay. They are common contaminants of cultures in bacteriological and mycological laboratories. fumigatus, A. flavus and A. niger and other species are animal and human pathogens which cause a group of diseases collectively known as Aspergillosis. Aspergilli are employed in several industrial processes. Citric and gluconic acids are manufactured commercially by the use of Aspergillus niger. Aspergillus spp. are employed to extract number of enzymes and antibiotics. Aspergillus oryzae is used to make sake, an alcoholic beverage concocted from rice and to manufacture variety of fermented foods in Japan. Class: Pyrenomycetes The pyrenomycetes represent the highest developed members of unitunicate Ascomycotina. They produce ascocarps that are globose or flask shaped perithecia, rarely cleistothecia. The perithicia has an opening called ostiole through which the ascospores are liberated. The passage which connects the ostiole with the cavity of the ascocarp is lined with short hair like outgrowths called periphyses. The structure lying inside the perithecium constitute the centrum. It includes the asci and the paraphyses, which line the inner wall of the ascocarp. The asci are club shaped or cylindrical. 47

48 Classification: The class is divided into four orders viz. Erysiphales, Meliolales, Coronophorales and Sphaeriales, which includes several families. Among the several families, the family Ophistomataceae, some genera of Melanosporaceae (Chaetomium, Chaetomidium) and and Microascaceae (Microascus) show similarities with the Plectomycetes and are intermediate between Plectomycetes and Pyrenomycetes. Family: Melanosporaceae: The family includes genera which produce often beaked and ostiolate perithecia containing spherical or globose, evanescent asci. The members are mostly saprobes growing in soil, on plant debris, dung etc. and some are parasite. Genus: Chaetomium Chaetomium is an important cellulose degrading fungus and is found growing on paper, fabrics and other cellulose rich materials. Some species are thermophilic and coprophilous frequently inhabiting manure heaps. The genus has about 80 species and is easily identified by its unmistakable perithecium. It has a long beak and is covered with hairs. The fungus is named on this character (Greek, chaite long hair). The hairs are of two type s (Fig.29): In C. globosum curly at top and straight at the base and in C. thermophile dichotomously branched above and mycelloid below. The asci are stalked, club shaped, cylindrical or oval and produced in a basal tuft. These gelatinise early and the ascospores lie freely in the cavity. The ascospores are released passively in an oozing mass of mucilage. Conidia are not produced by most of the species and dissemination of the fungus is brought about solely by ascospores. Economic Importance: The members are mostly saprobic growing on soil, plant debris, dung etc. C. thermophile is a thermophilic, cellulolytic and coprophillous species. C. globosum is an important cellulose degrading species. Class: Discomycetes (The Cup Fungi) The fungi producing unitunicate asci in apothecium are placed in the class, Discomycetes. The typical apothecium is sessile or stalked, cup shaped structure (hence the name cup fungi). These vary drastically in size from minute and hardly visible to several centimeters in diameter. They may be beautifully coloured, fleshy and moist in texture. 48

49 Classification: The following are the orders in the class- Discomycetes. 1. Medeolariales 2. Lyttariales 3. Tuberales 4. Pezizales 5. Phacidiales 6. Ostropales 7. Helotiales The members of all the orders form epigean ascocarps except for the order Tuberales which forms hypogean ascocarps. They are also distinguished by the mode of ascus dehiscence i.e. through a pore (Inoperculate) or an operculum or slit (Operculate). In some of the discomycetes, either operculate or inoperculate, the ascospores are released explosively in form of a visible miniature cloud drifting like smoke. The violent release of the ascospores is often accompanied by a hissing sound (Puffing). Both the asci and the paraphyses are phototrophic and their tips are always bent towards incident light. This orientation of the asci ensures smooth upward discharge of ascospores. The ascospores are large, usually elliptical and are discharged violently and in one lot. On the basis of ascospore characteristics of the species of the genus Peziza fall into two series. 1. Those producing smooth walled spores without oil drops 2. Those producing spores ornamented by warts or ridges and usually containing two large oil drops. The ascospores on germination at the suitable substratum, give rise to haploid mycelium of uninucleate cells. Life cycle: The fungi reproduce asexually by producing conidia. The conidial stage is known as Oedocephalum or Chromelosporium. Their efficacy in disseminating the fungus is doubtful. The common means of propagation is by sexual means. But they lack the sex organs. The sex organs are replaced by undifferentiated cells. Plasmogamy involves somatogamy between hyphae of opposite strains (in heterothallic species) or between two cells of the same hypha (in homothallic species). The cell that receives the male nucleus and becomes dikaryotic acts as the female cell. Ascogenous hyphae arise from this cell and develop asci at their apices. The vegetative hyphae weave a peridium surrounding the asci resulting in the formation of apothecium. Order: Pezizales The order includes the operculate Discomycetes which are found in soil, wood, dung and plant debris. The apothecia are formed above ground (rarely underground), are of diverse shapes, brightly colored and minute (hardly visible) to large size. It is a big order having 2 suborders and 7 families. 49

50 Family: Pezizaceae The members of the family produce apothecia, which are sessile or feebly stalked and usually cup or disc shaped, found growing on dung, soil, rotting wood etc. Genus: Peziza E g. Peziza ammophila, P. aurantia. Peziza with over 100 species is the most common genus. The cupulate apothecia (flattened in some species) are formed on rotten wood, manure heaps and soils rich in organic matter (Fig.30). Characteristic features: The apothecium has an exposed hymenium which lines the interior of the cup and consists of elongated asci (exhibiting various stages of development) and paraphyses. After liberation of the ascospores the apothecium disintegrates but the underground mycelium persists and forms apothecia again next season. This is repeated innumerable times until the mycelium is destroyed. Economic Importance: The members of the class Discomycetes are saprobes and bring about decomposition of dead organic matter. Some of members belonging to order Tuberales like Tuber (Truffles) The fruiting bodies are used as food and is highly priced. Some of these fungi cause important plant diseases. Eg. Monilia fruticola (causes brown rot of stone fruits), Sclerotinia sclerotiorum (causes several vegetable diseases). Subdivision: BASIDIOMYCOTINA The basidiom ycetes are regarded as the most highly developed group of fungi. They are characterized by several distinct features. The most important being the production of basidiospores. These are the sexual spores or meiospores, formed after karyogamy and meiosis. The basidiospores lie externally on the basidium. A typical basidium is unicellular, cleb shaped structure borne terminally on dikaryotic hyphae. It bears four basidiospores on projections called sterigmata. There are basidia which are septate (transversely or vertically) and are called phragmobasidia. Some produca basidia which develop from a special thick walled resting spores formed by dikaryotic hyphae called the teleuto or teliospores. The life cycle of basidiomycotina includes three types of mycelia called primary mycelia, which is formed by germination of basidiospores, consists of haploid, monokaryotic, septate hyphae. The secondary mycelium consists of dikaryotic hyphae, the cells of which contain two nuclei of opposite mating type brought together during plasmogamy. 50

51 The tertiary mycelium consists of specialized dikaryotic hyphae which participates in the formation of fruiting body, the basidiocarp. They produce curious structures called clamp connections formed during cell division in dikaryotic secondary hyphae having dolipore septum. The dolipore septum is an important characteristic feature of basidiomycotina. The septum flares up in the middle of the hyphae to form a barrel shaped pore called dolipore. Both the open ends of the pore are covered by a double membraned pore cap called paranthesome. Reproduction: 1. Unlike Ascomycotina, asexual reproduction is not common in the Basidiomycotina. Nevertheless budding, fragmentation, conidia, arthrospores and oidia contribute their share in reproduction. 2. Distinguishable sex organs are not formed in basidiomycotina except in Puccinia. However the three fundamental events of sexual reproduction viz. Plasmogamy, karyogamy and meiosis take place. Plasmogamy can be brought about by somatogamy or spermatization, and also involves dikaryotization of a monokaryotic mycelium by a dikaryotic hyphae. Fruiting Bodies: The fruit bodies of Basidiomycotina are called basidiocarps and are the most attractive and beautiful of all fungi. They are of various shape, size and texture. They may be open from the beginning called gymnocarpous, or only at later stage hemiangiocarpic and some are permanently closed called angiocarpic. Basidiospores are discharged passively, while violent discharge occurs as a rule in the class Hymenomycete s. The basidiospores which are violently discharged are called ballistospores. Classification: Sub division Basidiomycotina has been classified into three classes based on i. The presence or absence of basidiocarp. ii. Angiocarpic, hemiangiocarpic or gymnocarpic nature of basidiocarp. iii. The septate or unseptate nature of basidia iv. Explosive or passive discharge of the basidiospore. The three classes are Class: Hymenomycetes 1. Teliomycetes 2. Hymenomycetes 3. Gasteromyces This is the largest class of Basidiomycotina, which include interesting and important fungi popularly known as Gelly fungi, Pol ypores, Mushrooms, Toad-stools, Coral fungi etc. The characteristic features are The formation of basidia in a hymenium. Gymnocarpous or hemiangiocarpous nature of basidiocarp. The explosive discharge of basidiospores called ballistospores. The Hymenomycetes are divided into two subclasses 51

52 Subcla ss: Phragmobasidiomycetidae Subclass: Holobasidiomycetidae The subclass Holobasidiomycetidae includes various, members among which important are the Mushrooms and Toad-stools. Order Agaricales: (The gill fungi) The legendary mushrooms and toad-stools which first attracted the attention of man towards fungi, belong here. Family: Agaricaceae Genus: Agaricus These ae also called as gill fungi. The species of Agaricus grow saprophytically on humus rich soil, decaying leaves, wood, manure heaps etc. the fruiting body is umbrella shaped and is eaten with avidity by people all over the world. The fruit bodies are ephemeral and survive only for a few days. However the fungus is not lost, it exsist by the extensive underground mycelium which continues growing. 52

53 The Basidiocarp: The basidiocarp is umbrella shaped, consisting of a stem (stipe) and a pileus, all made of dikaryotic mycelium (Fig.31). 1. The Stipe: It is negatively geotrophic and holds the cap high above the ground level to enable the vertically falling spores to be easily drifted away by wind. It also helps in transport of food particles to the pileus. 2. The Pileus: It is convex, fleshy structure, which later becomes flat. Its upper surface is white or colored- red, yellow, purple, orange, pink, green or brown. The lower surface bears vertically hanging gills, which radiate from the periphery and converge towards the stipe. Gills are separated from each other by a distance of about 0.5 mm. A vertical 53

54 tangential section of the pileus shows wedge shaped gills covered with hymenium. The hymenium consists of elongated, club shaped basidia of different lengths arranged at right angles to the surface of pileus. Intermingled with basidia lie basidioles, which are young aborted or sterile basidia (also called paraphyses). The gills are positively geotrophic. They are made up of elongated cells in the centre called trama (fig.32), from which short branches run obliquely towards the surface to form a compact mass of hyphae called subhymenium. The basidiospores are violently discharged. The fruit body which exists for 2 or 3 days produces half a million spores per minute. The basidiospores may be 2 or 4 mating types. On germination, they give rise to primary (monokaryotic) hyphae of different mating types. When the hyphae of opposite mating types come together and anastomose, somatogamy occurs resulting in the formation of a dikaryotic cell. A dikaryotic hypha originates from this cell which grows extensively and give rise to secondary mycelium. On reaching a particular stage, the umbrella shaped basidiospores are formed. The dikaryotic hyphae which forms the basidiocarp are called the tertiary mycelium. The basidiocarp lives a short but vigorous life of 2 3 days. When it falls and degenerates, the fungus survives through the mycelium which spreads underground extensively. Economic Importance: Some mushrooms are edible and irresistible for their flavours, rich in proteins and vitamins like Agaricus campestris. Some mushrooms are hallucinogenic eg. Psilocybe, the sacred mushroom. The hallucinogenic chemical has been extracted and named as Psilocybin. These are consumed by Mexican Indians during religious rites and hence the name sacred mushroom. Several mushrooms are deadly poisonous and earned such dreadful names such as death chair (Amanita phalloides), the destroying angel (A. verpa). Some mushrooms eg. Armillaria mellea, Clitocybe illudens and Collybia are luminescent and glow in dark. 54

55 Sub division: DEUTEROMYCOTINA This subdivision includes all those fungi that do not have a sexual (perfect) stage, as well as those where none has so far been demonstrated. The conidial stages of these fungi are very similar to those of some well known Ascomycetes. It is assumed, therefore that the fungi imperfecti may represent conidial stages of Ascomycetes whose ascus stages has not yet been discovered or has been lost in the course of evolution. On the other hand, even the fungi imperfecti are not completely asexual. Parasexuality has been demonstrated in these, as well as in Basidiomycetes and some Ascomycetes. Thus, they exhibit the processes of plasmogamy, karyogamy and meiosis, but these do not occur at defined locations of the vegetative body or at special developmental stages (i.e they occur at random). 55

56 The Deuteromycotina has been called a dust bin group to accommodate asexual fungi until their true taxonomic place is determined. Classification: G.C. Ainsworth (1966) proposed a classification of Deuteromycotina which is accepted by most of the mycologists. He divided the subdivision into 3 classes. 1. Class: Blastomycetes Eg. Candida albicans, Cryptococcus neoformans. 2. Class: Hyphomycetes Eg. Verticillium albo-atrum, Fusarium oxysporum. 3. Class: Coelomycetes Eg. Colletotrichum etc. Class: Hyphomycetes Fungi Imperfecti, forming spores directly on the hyphae or on sporophores (free or aggregated), but never in pycnidia or acervuli are placed in Class Hyphomycetes. It is classified into four families viz. Moniliaceae, Dematiaceae, Tuberculariaceae and Stilbaceae (Saccardo 1880). Subramanian (1962) believed that more sections would be required to accommodate the Indian and other tropical hyphomycetes and proposed 25 sections. He later recognized 5 distinct families characterized by a particular spore type, as 1. Torulaceae 2. Helminthosporiaceae 3. Tuberculariaceae 4. Bactridiaceae 5. Geotrichaceae Family Tuberculariaceae The family is characterized by production of conidia on phialides, the phialospores. Genus: Fusarium The genus is an important plant pathogen causing wilt and root rot diseases of several economically important plants. It is more prevalent in tropical countries. Vegetative structure: The hyphae are hyaline (fig.33), branched and septate. Conidia are formed in slimy, effuse sporodochia called pionnotes, or sometimes scattered on the mycelium. The conidiophores are quite short, simple or branched, septate, bearing a terminal phialide. The phialides are subulate i.e. widest at the base, narrowing to a point. The conidia which are slimy are of two types 1. Microconidia (one celled, oval or comma shaped, pyriform or elongate) 56

57 2. Macroconidia (which are hyaline or pale, spindle shaped with pointed ends, hence the name fuscus = spindle). Chlamydospores if present are formed on the hyphae. Microconidia may be present or lacking. 57