REPRODUCTION IN FUNGI -REPRODUCTIVE STRUCTURES

 Fungi reproduce by means of their propagules.
 In most fungi the propagules are differentiated as spores.
 But in some fungi the stromatic aggregations of hyphae like the sclerotia also perform the function of propagation.
 The simple or branched spore-bearing hyphae are known as sporophores, but in some fungi the spores may be formed directly by the hyphal cell e.g. chlamydospores.
 In general spore formation starts when the vegetative growth has reached a certain development.

Types of sporophores

 Spore bearing or sporogenous organs (sporophores) develop as special branches from the vegetative hyphae.
 There are two types of sporophores viz., simple and compound. The spore bearing branches usually arise vertically and may be distinctly branched.
 When these branches bear sporangia they are called sporangiophores (as in Oomycetes of Mastigomycotina and Zygomycotina When the spore bearing branches bear conidia they are called conidiophores (as in Ascomycotina and Deuteromycotina).
 These sporangiophores and conidiophores are called simple or filamentous sporophores.
 Aggregation of hyphae from stromatic or semistromatic structures and grows into compound sporophores.
 They contain or bear layers of sporogenous cells and spores and form the fructifications and fruit bodies. e.g. stipes formed by germination of sclerotia in Ascomycotina and by higher basidiomycotina.
 Types of sporophores Spore bearing or sporogenous organs (sporophores) develop as special branches from the vegetative hyphae.
 There are two types of sporophores viz., simple and compound. The spore bearing branches usually arise vertically and may be distinctly branched.
 When these branches bear sporangia they are called sporangiophores (as in Oomycetes of Mastigomycotina and Zygomycotina When the spore bearing branches bear conidia they are called conidiophores (as in Ascomycotina and Deuteromycotina).
 These sporangiophores and conidiophores are called simple or filamentous sporophores.
 Aggregation of hyphae from stromatic or semistromatic structures and grows into compound sporophores.
 They contain or bear layers of sporogenous cells and spores and form the fructifications and fruit bodies. e.g. stipes formed by germination of sclerotia in Ascomycotina and by higher basidiomycotina.

Fructifications and fruit bodies

 The sporophores bear fruiting bodies or form fructifications, which may be asexual or sexual in nature.
 In lower fungi Plasmodiophoromycetes, Chytridiomycetes, Oomycetes and Zygomycotina) asexual spores are usually enclosed in simple sacs called sporangia or zoosporangia.

In higher fungi (Ascomycetes and Basidiomycetes) complex aggregates of spore bearing hyphae are formed and supporting and protective tissues surround it.

 These complex structures are called as spore fruits or fructifications (L.fructus = fruit).

Asexual fructifications

 In fungi conidiophores are grouped together to form specialized structures such as synnemata (sing. synnema) and sporodochia (sing. sporodochium) or produced in fructifications known as pycnidia (sing. pycnidium) and acervuli (sing. acervulus).
a.Synnema or coremium
 Synnema or Coremium (pl. coremia) Consists of a group of conidiophores often united at the base and part way up the top.
 Conidia may be formed along the length of the synnema or only at its apex.
 The conidiophores comprising a synnema are often branched at the top with the conidia arising from the conidiogenous cells at the tips of the numerous branches. e.g. Deuteromycotina (Arthrobotryum sp, Penicillium claviforme, Doratomyces stemonitis, Ceratocystis ulmi.synnema: (pl. synnemata; syn. coremium) compact or fused, generally upright conidiophores, with branches and spores forming a headlike cluster

b.Sporodochium
 Sporodochium is a fruiting body in which conidiophores arise from a central cushion-like aggregation of hyphae.
 The conidiophores are packed tightly together and are generally shorter than those composing a synnema. e.g. Epicoccum, Nectria. sporodochium: (pl. sporodochia) Superficial, cushion- shaped asexual fruiting body consisting of a cluster of conidiophores
c.Pycnidium
 Pycnidium is a globose or flask-shaped body, which is lined on the inside with conidiophores. e.g. Septoria ,Phoma, Ascochyta, Leptosphaeria. Pycnidia may be completely closed or may have an opening.
 The opening or mouth of pycnidium is called ostiole (L. ostiolum = little door). They may be provided with a small papilla or with a long neck leading to the opening.
 Pycnidia vary greatly in size, shape, colour and consistency of the pseudoparenchymous wall.

 The wall of pycnidium is called peridium (pl. peridia; G. peridion=small leather pouch) and it is composed of multicellular layer, as fungal tissues.
 Pycnidia may formed superficially or sunken in the substratum.
 They may be formed directly by the loose mycelium or may be definitely stromatic.
d.Acervulus
 Acervulus (pl. acervuli) is a fruiting structure commonly found in the order Melanconiales (Deuteromycotina).
 It is typically a flat or saucer-shaped mass of aggregated hyphae bearing short conidiophores in a compact layer.
 Intermingled with the conidiophores, setae (sing. seta; L. seta = bristle) are found.
 Setae are long, pointed, dark coloured, sterile structures.
 In nature acervuli are produced on plant tissues subepidermally or subcuticularly and becomes erumpent on maturity. e.g. Colletotrichum.

Sorus

 Sorus (pl. sori; Gr. Soros = heap) is a little heap of sporangia or spores. It may be naked or covered by a thin false membrane, as in smuts, or protected by the epidermis as in rust diseases or white blister or white rust (Albugo spp.).
 The structures break open at maturity and release the spores within, in the form of rust, which is characteristic of these diseases.

Sexual fruiting bodies

a.Pycnium
 Pycnium or spermagonium (pl. pycnia; Gr.pycnos = concentrated) is a fruit body, which is similar to pycnidium and is formed in sexual cycle of rust fungi.
 Pycnia are produced from primary uninucleate mycelium growing in the tissues of the host.
 They may be determinate or indeterminate in growth and may form in a subcuticular, subepidermal or subcortical fashion.
 Pycnia may be flask-shaped, conical, flat and sprawling.
 The flask-shaped type is more typical, The mouth of the flask (called ostiole) is lined by a bunch of unbranched, tapering, pointed, orange coloured hairs called ‘periphyses’ (sing. periphysis; Gr. peri = around + physis = a being, a growth).
 Periphyses develop from the upper edge of spermagonial wall, converge toward a central point and curved upward.
 The tips of the periphyses, pushing against the host epidermis from below, rupture it and protrude above it through the opening they have created.
 Among the periphyses thinner-walled and branched hyphae called flexuous hyphae or receptive hyphae are found.
 The pycnial wall cells send many closely -packed, elongated, tapering, unbranched uninucleate sporogenous cells or spermatiophores (Gr. spermation = little seed+ phoreus=bearer) in the cavity.
 These spermatiophores give rise to a series of uninucleate spermatia (sing. spermatium Gr. spermation=little seed) or pycnospores in a basipetal fashion.
 Pycnospore is a non-motile, uninucleate, unicellular spore-like male structure that empties its contents into a receptive female structure during plasmogamy.
 Pycnospores are variously regarded as gametes or gametangia.
 The pycnospores produced in large numbers are exuded up, out of the pycnial cavity through the ostiole in a droplet of nectar (a thick, sticky, fragrant, sweet liquid). e.g. pycnium is produced by Puccinia graminis tritici in the alternatehost, barberry (Berberis vulgaris).
b.Aecium
 Aecium (pl. Aecia: Gr. aikia = injury) is also formed during sexual cycle. Aecium is a shallow or deep cup-shaped structure produced in a leaf and located in the lower portion and break through the lower epidermis.
 Aecia may be with or without peridium.
 It is a group of typically dikaryotic hyphal cells within the parasitized host that give rise to chains of dikaryotic aeciospores.
 Larger aeciospores are alternated with small, sterile intercalary cells or disjunctor.
 In most rust fungi the peripheral cells of the aecial base successively divide and gives rise to a wall that surrounds the spore chain in the form of a cup.
 The wall is known as ‘peridium‘. In a young aecium that has not broken the host epidermis, the peridium surrounds the spore chain on all sides, forming a complete dome over them.
 When the aecium matures, the spore chains push through the roof of the peridium and the aeciospore are released.
 The torn peridium forms a lip-like structure around the aecial cup.
c.Ascocarps
 Ascocarp (Gr. askos = sac+ karpos =fruit) is a fruiting body that contains asci and ascospores.
 Ascomycetes fungi with few exceptions produce ascocarps.
 They are in various forms like spherical, flask-shaped, cup-and saucer shaped and pod-shaped.
 They may be closed in some, and provided with a narrow wide opening in others.
 Ascocarps may formed singly or in groups.
 They may be superficial, erumpent or deeply embedded in the substratum.
 The substratum may be composed entirely of hose tissue, or it may be a hyphal stroma or in which the ascocarps form.

There are four categories ascocarps.

i.Cleistothecium:
 Asci are produced in completely closed ascocarp.
ii.Perithecium: It is more or less closed
 ascocarp; but at maturity it is provided with ostiole through which the ascospores escape.
iii.Apothecium: Ascocarp produce asci in open.

iv.Ascostroma or Pseudothecium:
 Stromatic ascocarp, which bears asci directly in locules within the stroma.
i.Cleistothecium: (pl. cleistothecia; Gr. kleistos = closed + theke = case).
 Cleistothecium or cleistocarp is a closed ascocarp and has no ostiole.
 It is deep brown to black in colour, more or less spherical and often provided with appendages on its body, which serve as organs of anchorage and help in dissemination.
 They may contain one to several asci, which discharge their spores violently.
 Each cleistothecium of Sphaerotheca and Podosphaera contains a single ascus whereas each cleistothecium in Erysiphe, Microsphaera, Uncinula, Leveillula and Phyllactinia contain several asci.
 Cleistothecia crack open at maturity by swelling of the contents.
 They are found in Eurotiales and Erysiphales (powdery mildews or white mildews or true mildews.
 The matured cleistothecia of most Erysiphaceae are provided with characteristic appendages that vary considerably in length and character, and which together with the number of asci developed in the cleistothecium, form the basis for differentiation of genera.
 Cleistothecial appendages are of four types viz. Myceloid appendages: Appendages resemble somatic hyphae in flaccidity and indefinite growth. e.g. Erysiphe, Sphaerotheca and Leveillula.
 Appendages are rigid, spear-like with a bulbous base and pointed tip. e.g.Phyllactinia.
 Appendages are rigid with curved tips e.g. Uncinula, Pleochaeta.
 Appendages are rigid with dichotomously branched tips. e.g. Microsphaera, Podosphaera.
ii.Perithecium
 Perithecium (pl. perithecia, Gr. peri = around + theke = a case) is a flask -shaped ascocarp with a wall of its own.
 It is provided with a narrow ostiole and may possess a short or a long neck through which the asci are released at maturity.
 The asci are arranged in a regular manner and are lined the inside wall.
 The asci are intermingled with sterile filaments called paraphyses, which help the asci in with sterile filaments called paraphyses, which help the asci in nutrition and dispersal.
 The paraphyses, which are rigid and appear in the ostiole are called periphyses.
 The perithecia ma y be borne singly or in groups.
 In Sphaeriales and Hypocreales, the perithecia are borne on or embedded in a mass of fungal tissue termed the ‘perithecial stroma’ and these are found in Xylariaceae and by Cordyceps and Claviceps.
 In some cases, in addition to the perithecial stroma, a fungus may develop a stromatic tissue on which or within which asexual spores or conidia develop. e.g. Nectria cinnabarina (Coral -spot fungus) forms pink conidial stromata.
 In perithecia, the ascus wall is single and is called ‘unitunicate’ (L. unus=one+tunica =coat, mantle).
 Perithecia are produced by fungi in Hypocreales (Hypocrea , Nectria, eratocystis, Podospora, Chaetomium, Xylaria, Ustulina, Rosellinia, Claviceps and Cordyceps) in Sphaeriales.

iii.Apothecium
 Apothecium (pl. Apothecia; Gr. apotheke=store house) is an open ascocarp.
 It has a broad opening and is either cup or saucer shaped with asci arranged in a palisade layer within.
 It is usually fleshy or leathery in nature.
 An apothecium consists of three parts viz. hymenium, hypothecium and excipulum.
 The hymenium is the layer of asci that lines the surface of hollow part of the disc, cup or saddle.
 It is made up of club-shaped or cylindrical asci, usually with many or few paraphyses among them.
 These paraphyses may be as long as the asci, longer or somewhat shorter.
 In some apothecia, the tips of paraphyses may be branched and the tips of branches may unite above the asci and form a layer called the epithecium (pl. epithecia; Gr. epi =upon+ theke =a case).
 The ‘hypothecium'(pl. hypothecia; Gr. Hypo=under+ theke =a case) is a thin layer of interwoven hyphae, which is found immediately below the hymenium.
 The apothecium proper (i.e., the fleshy part of the ascocarp that supports the hypothecium and hymenium) is called excipulum (pl.

excipula ; N.L. excipulum=receptacle), Excipulum consists of two parts viz., ectal excipulum and medullary excipulum.

 Ectal excipulum is the outer layer of the apothecium and the medullary excipulum is the inner portion. e.g. cup fungi (Pyronema, Ascobolus, Peziza, Morchella etc) in Pezizales and Sclerotinia, Trichoscyphella etc.) in elotiales.
iv.Pseudothecium
 Pseudothecium or ascostroma (pl. ascostromata; Gr. askos = sac + stroma = mattress, cushion) like perithecium is a flask-shaped ascocarp provided with an ostiole through which the asci are discharged.
 In pseudothecium asci are directly formed in a cavity (locule) within the stroma.
 The stroma itself thus forms the wall of the ascocarp. In pseudothecium the ascus wall is double i.e. the ascus is bitunicate.
 The walls are separable.
 The outer wall does not stretch readily but ruptures laterally or its apex to allow the stretching of a inner layer. e.g. Cochliobolus, Pyrenophora, Ophiobolus, Pleospora, Leptosphaeria of the class Loculoascomycetes.

d.Basidiocarps
 Basidiocarp (Gr. basidion=small base + karps = fruit) is a fruiting body, which bears basidia and basidiospores.
 Basidia are borne on the under surface of fruit body.
 Basidia bear basidiospores exogenously usually on projections called sterigmata.
 Basidia are typically formed in definite layers called hymenium

(pl. hymenia; Gr. hymen=membrane).

 Hymenium is composed of basidia and large sterile structures called cystidia (sing. cystidium; Gr. kystis =bladder + -idion = dimin. Suffix).
 They are highly developed and have compound structure. Basidiocarps may be thin and crust-like, gelatinous, cartilaginous, papery, fleshy, spongy, corky or woody.
 They may vary in size from microscopic to a metre or more in dia.
 Most fungi in basidiomycotina except smuts (Ustilaginales) and rusts (Uredinales) form basidiocarps.
 They include mushrooms, (Agaricus, Pleurotus, Volvariella), shelf fungi, coral fungi (Clavariaceae) puff balls (Lycoperdaceae- Lycoperdon sp.) earth stars, (Geastraceae-Geastrum stinkhorns sp. (Phallales -phallus) and birds-nest fungi. (Nidulariales-Nidula sp.).
 The main body of the fungus in each case is the extensive mycelium, which usually goes unnoticed.
 Basidiocarp may be open from the beginning, exposing their basidia, or they may open at a later stage, or even remain closed.
 In closed basidiocarps the spores are liberated only on the disintegration of the basidiocarp or with its accidental fracture by external forces (e.g. Lycoperdon).
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