Botany - B.Ye. Yakubenko 2017

Part Two. The System of the Organic World
Chapter V. The System of the Organic World
5.5. KINGDOM TRUE FUNGI MYCOTA (FUNGI)

According to modern views, Fungi constitute an independent kingdom. These are eukaryotic heterotrophic organisms that lack Plastids and chlorophyll. Fungi combine features of both plants and animals. They share with plants unlimited growth, the absence of motile forms in the vegetative state, and absorptive Nutrition, while with animals they share the presence of Chitin in The Cell wall, urea in their METABOLISM, heterotrophic nutrition, and Glycogen as a reserve nutrient. The body of fungi is called the mycelium and consists of individual threads known as hyphae. Only in primitive lower fungi is the body represented by a plasmodium or a rudimentary mycelium—a rhizomycelium.

Cell Structure. The Cell wall of the mycelium consists of Polysaccharides and chitin. The protoplast contains one, two, or several nuclei and Cytoplasm with Organelles. Plastids are absent, but there are Mitochondria, Lysosomes, Ribosomes, a Golgi apparatus, an Endoplasmic reticulum, and vacuoles. Reserve nutrients include volutin, glycogen, and oil; starch is not stored.

The fungal mycelium can be non-cellular and multinucleated, undivided by perforated septa into nucleated Cells (aseptate), or multicellular (septate). Mycelial hyphae exhibit unlimited apical growth and branch extensively; tightly intertwining, they form a false tissue called plectenchyma. Hyphae penetrate the substrate and absorb nutrients from it across their entire surface.

Septate mycelium can take on various specialized forms: mycelial cords, rhizomorphs, and sclerotia. Mycelial cords are bundles of parallel hyphae with a densified peripheral layer. Rhizomorphs consist of massive, dark-colored bundles of hyphae, whereas sclerotia are compact structures formed of tightly intertwined hyphae with a reserve of nutrients, mostly dark in color, which serve to endure adverse conditions or for reproduction.

Nutrition of fungi. Fungi are heterotrophs. Depending on the substrate, they are divided into saprotrophs (dead substrate), parasites (living substrate), and symbionts (mutualistic relationship). Saprotrophs can be obligate (obligatory) and facultative (optional) and play the same role as Bacteria by mineralizing organic remains, while parasites cause diseases in plants, animals, and humans and can also be obligate or facultative. Symbiotic fungi enter into a partnership with plant roots to form mycorrhiza or become part of a lichen thallus.

REPRODUCTION OF FUNGI can be vegetative, asexual, and sexual. Vegetative Reproduction occurs through fragments of the mycelium, sclerotia, budding, or The breakdown of the mycelium into separate thick-walled cells called chlamydospores, or thin-walled ones known as oidia.

Asexual reproduction is carried out via zoospores, spores, and conidiospores. They can be formed endogenously within sporangia or exogenously at the ends of specialized mycelial outgrowths called conidiophores. Spores germinate into the fungal mycelium.

The Sexual process in fungi can take various forms: hologamy, isogamy, heterogamy, oogamy, zygogamy, gametangiogamy, and somatogamy. In many fungi, Selection/8.html">Asexual and sexual sporulation alternate, and therefore three phases may alternate in The life cycle: the haploid phase, lasting from the moment of Meiosis until the fusion of Gametes, gametangia, or mycelial hyphae; the dikaryotic phase, lasting from the fusion of protoplasts (plasmogamy) and the approximation of nuclei to form dikaryons until nuclear fusion (karyogamy), which is characteristic of highly organized fungi; and the diploid phase, lasting from karyogamy until the onset of meiosis.

In most fungi, sexually derived spores develop after the completion of the sexual process. In lower fungi, the products of the sexual process are mostly resting spores (oospore or zygospores). In higher fungi, sporangia in the form of asci or basidia develop from the zygote. Within them, eight ascospores or four basidiospores are formed from the diploid Nucleus via meiosis.

Ecological groups of fungi include: soil fungi (saprotrophs, predatory fungi), coprophils living on humus, keratinophiles inhabiting Hair, horns, and hooves; aquatic fungi (saprotrophs, parasites); PLANT AND ANIMAL pathogenic fungi; mycorrhizal symbiont fungi; and fungi that settle on wood (xylotrophs) and various industrial Materials such as Glass, metal products, cardboard, and paper, causing damage to them.

The kingdom of fungi comprises about 100,000 species. Fungi are traditionally divided into five phyla: Chytridiomycota, Zygomycota, Ascomycota (sac fungi), Basidiomycota (club fungi), and an artificial group of anamorphic, mitosporic, asexual, or imperfect fungi.

Class="center">5.5.1. Phylum Chytridiomycota (Chytridiomycota)

In fungi of this phylum, the vegetative body appears as a plasmodium or a poorly developed mycelium—a rhizomycelium (protomycelium). Asexual reproduction is carried out by zoospores with a single posterior flagellum. The sexual process may occur in the form of hologamy, isogamy, heterogamy, or oogamy. The phylum includes about 1,000 species and a single class, Chytridiomycetes. Most Chytridiomycota are parasites of freshwater and marine Algae, aquatic fungi, aquatic higher plants, and animals. The most widespread representatives of this class in Ukraine are Olpidium brassicae, which causes "black leg" in cabbage seedlings, and Synchytrium endobioticum, which causes potato wart disease. Infection by Olpidium is carried out by zoospores that reach the ROOT collar of cabbage seedlings with Water and penetrate the epidermal cells and subsequently the primary cortex. The protoplast of the parasite remains naked for a long time while its nucleus divides repeatedly, transforming it into a zoosporangium with numerous uniflagellate zoospores and a long discharge tube that ruptures the root cells, allowing the zoospores to escape and infect new plants. Under certain conditions, zoospores can behave like gametes. By fusing in pairs, they form a biflagellate dikaryotic zygote in the soil, which infects the host cell. Here, the zygote cell develops a thick wall and forms a cyst. The root collar of the seedling turns black, dies off, and the plant perishes. The following spring, the dikaryotic cyst cell transforms into a zoosporangium. First, the haploid nuclei within it fuse, and then the diploid nucleus undergoes meiosis followed by multiple mitotic divisions, forming numerous zoospores that initiate primary plant infection.

Synchytrium endobioticum causes dry rot of potato tubers or wart disease. Infection also occurs via zoospores that penetrate young tubers, stimulating accelerated division of epidermal and flesh cells. As the tuber grows, an outgrowth forms with very hard cell walls inside it. Within the tuber, the parasite transforms into a summer cyst, which later germinates to produce zoosporangia containing A large number of zoospores. The zoospores infect new tubers. The tuber enlarges, becomes deformed, and rots during storage. Chytridiomycota are one of the most ancient groups in the Fungi kingdom.

5.5.2. Phylum Zygomycota (Zygomycota)

This phylum includes fungi with a well-developed filamentous coenocytic mycelium, although cross-walls and septa may appear in it at maturity. Asexual reproduction is carried out by sporangiospores or conidia. Sporangiospores are formed inside a sporangium that rises above the mycelium on a sporangiophore. The sporangia are separated from the mycelium by a septum, and their multinucleated contents break down into numerous spores, which are released after the wall ruptures and are dispersed by the air. Zygomycete spores lack flagella, indicating their terrestrial lifestyle. The sexual process is zygogamy, which consists of the fusion of two undifferentiated multinucleated cells formed at the tips of mycelial hyphae. As a rule, hyphae of a heterothallic mycelium fuse—meaning they are morphologically identical but physiologically different. The sexual product is a zygospore. Under favorable conditions, the zygote germinates into a germ sporangium. Within it, haploid nuclei are formed via meiosis, from which haploid spores develop As a result of multiple mitotic divisions.

The phylum comprises about 400 species belonging to two classes and 11 orders, among which we consider Mucorales and Entomophthorales. Within the order Mucorales, saprophytic fungi of the genus Mucor are well known. These fungi live in soil or on other substrates, and their spores are constantly present in the air. Food and feed contaminated by mucoralean fungi spoil, and their consumption causes poisoning known as mucormycosis. Some of these fungi possess high enzymatic activity or produce carotenoids, Lipids, and acids, and are used in industry to obtain these substances or food products that are especially popular in Asian cuisine.

Entomophthoraceous fungi are parasites of terrestrial insects and other Arthropods and can be utilized in biological control Methods against harmful insects.

5.5.3. Phylum Ascomycota (Sac Fungi) (Ascomycota)

These are fungi possessing a well-developed multicellular haploid mycelium divided by septa with pores into uni- or multinucleated cells. The main characteristic of the phylum is The formation of sexually derived spores—ascospores—which are formed within sacs (asci). Asexual reproduction occurs via conidia, which are spores that develop exogenously on the haploid mycelium upon specialized hyphae known as conidiophores in the form of cell chains.

The sexual process is gametangiogamy, meaning the fusion of two multinucleated cells—gametangia—whose contents are undifferentiated into gametes. The male sex organ is called the antheridium, and the female one is the archicarp. The archicarp consists of an expanded part—the multinucleated ascogonium—and a narrowed tube called the trichogyne. During the sexual process, the trichogyne grows into the antheridium, and its contents, along with the male nuclei, flow into the ascogonium containing the female nuclei. Concurrently, the protoplasts fuse, and the nuclei approach each other, forming dikaryons. The ascogonium begins to bud off ascogenous hyphae, and the dikaryons divide synchronously and migrate into the ascogenous hyphae. After some time, a single cell with one dikaryon—the mother cell of the ascum—is delimited at the tips of the ascogenous hyphae. At The final stage of the sexual process, the nuclei of the dikaryon fuse to form a diploid nucleus. This nucleus undergoes meiosis and then mitosis, resulting in the formation of eight nuclei within the ascum, around which ascospore cells are formed. As ascospores mature inside the asci, the osmotic pressure increases, causing the wall of the ascum to rupture and the ascospores to be forcibly discharged.

In more primitive ascomycetes, sex Organs are not formed, and the sexual process occurs via the copulation of two vegetative cells. As a result of the sexual process, an ascus develops containing eight, or less frequently four, ascospores. In some ascomycetes, asci develop directly on the mycelium, whereas in higher ones, they form within fruiting bodies—cleistothecia, perithecia, or apothecia.

Cleistothecia are closed fruiting bodies with a dense wall—the peridium—and Appendices of various shapes. Ascospores are released either after the breakdown of the wall or when it cracks. Perithecia are semi-open flask-shaped fruiting bodies, and spores are actively expelled through the perithecial opening. Apothecia are saucer-shaped or disc-shaped open fruiting bodies; on their surface, a hymenium develops, which is a spore-bearing layer consisting of asci and sterile filaments known as paraphyses.

The phylum counts about 30,000 species, which are divided into six classes: Saccharomycetes, Schizosaccharomycetes, Taphrinomycetes, Ascomycetes, Neolectomycetes, and Pneumocystidomycetes.

The class Saccharomycetes mainly comprises unicellular forms whose cells are capable of budding and division. Under unfavorable conditions, two vegetative cells copulate to form an ascus containing ascospores. Most saccharomycetes are saprotrophs developing on sugar-rich substrates such as The surface of fruits and berries, and floral nectars. Under certain conditions, they are capable of causing Alcoholic Fermentation. Baker's, brewer's, and wine Yeasts have great practical utility and are used in baking, winemaking, and the alcohol industry. Yeasts contain B-group Vitamins and are utilized in pharmacy to obtain vitamins, lipids, Enzymes, organic acids, etc.

Taphrinomycetes comprise about 100 species of parasitic fungi in which asci are formed on the mycelium. Their mycelium is well-developed, perennial or annual, penetrating intercellular spaces and plant tissue cells while secreting hormone-like substances (Cytokinins). These compounds stimulate the synthesis of phytohormones in the host plant, leading to organ deformation and pathological overgrowth. Infection occurs via ascospores. Taphrinomycetes mostly cause diseases in woody plants, such as witches' brooms on hornbeam and elm, hypertrophy of alder cones and birch catkins, or plum and cherry fruit pockets.

The class Ascomycetes includes highly organized fungi in which asci are formed within fruiting bodies following gametangiogamy. The class comprises numerous orders, of which Eurotiales, Erysiphales, and Hypocreales are central.

The order Eurotiales comprises fungi with cleistothecia as fruiting bodies and asexual reproduction via conidiospores. Most Eurotiales are saprotrophs inhabiting the soil, represented by the genera Aspergillus and Penicillium, both exhibiting a sexual process. Some species are parasites causing Human and Animal diseases such as dermatomycosis and histoplasmosis.

Erysiphalean fungi are predominantly parasites whose mycelium develops On the surface of photosynthetic organs; the mycelium attaches to leaves or stems using appressoria and feeds via haustoria that penetrate the chlorenchyma. They reproduce by conidiospores, and their sexual process is gametangiogamy. Fruiting bodies are cleistothecia. The greatest agricultural damage in Ukraine is caused by powdery mildew fungi of the genus Erysiphe, which infect wheat, rye, corn, and rice, as well as species of the genus Sphaerotheca, which parasitize currants, gooseberries, and roses. During mass outbreaks, they can reduce crop yields by 30–50%.

The order Hypocreales mainly comprises parasitic fungi featuring perithecia as fruiting bodies and The ability to form sclerotia. The most dangerous representative of this order is Claviceps purpurea, which infects over 200 plant species. Asexual reproduction during the growing season occurs via conidiospores, whereas during crop maturation, sclerotia form within the cereal spikelets whose flowers were infected by the parasite. Sclerotia contain about 30 toxic Alkaloids that, when entering flour, cause severe and even fatal poisonings in humans. At the same time, sclerotia are used in medicine and veterinary practice.

Other Representatives of the order, such as Nectria, cause a disease known as European apple tree Cancer, while fungi of the genus Gibberella yield the growth promoter gibberellin.

The order Pezizales includes fungi with apothecia as fruiting bodies, which vary significantly in both size and coloration. Apothecia range from 1 to 100 mm in diameter and display colors from bright red to brown or black. These are predominantly saprotrophic or even symbiotic fungi. In the forests of Ukraine, conditionally edible fungi of the genera Morchella (morels) and Gyromitra (false morels) can be found, although the latter may be toxic. Edible truffles (genus Tuber) form underground fruiting bodies and are among the most expensive fungi.

5.5.4. Phylum Basidiomycota (Basidiomycota)

These are higher fungi with a multicellular mycelium, with the phylum comprising about 30,000 species. Their sexual process is somatogamy. Sex organs are absent; instead, two haploid Cells of the primary mycelium—which grows from a basidiospore and consists of uninucleate haploid cells—fuse together. In homothallic species, hyphae of the same mycelium fuse, whereas in heterothallic species, fusion occurs between hyphal cells of mycelia grown from physiologically dissimilar spores. Initially, plasmogamy occurs, while the nuclei merely approach each other to form dikaryons. In binucleate cells, the nuclei divide synchronously, forming a secondary dikaryophytic mycelium, which dominates the reproduction cycle of basidiomycetous fungi. After a prolonged period of vegetative growth of the secondary mycelium, karyogamy takes place within its cells. This is the final phase of the sexual process. In each cell, the haploid nuclei of the dikaryon fuse to form a zygote, which then develops into a basidium. The diploid Nucleus of the basidium undergoes meiosis to produce four haploid basidiospores. A primary haploid mycelium grows from each basidiospore.

Thus, the sexual process occurs in two stages: 1) plasmogamy, resulting in the formation of dikaryontic cells and secondary mycelium; 2) karyogamy, during which the dikaryon nuclei fuse to form a diploid cell, the zygote. The zygote develops into a basidium, The Organ of sexual sporulation. Four basidiospores are formed exogenously on the basidia. The tubular outgrowths of the basidium that bear the basidiospores are called sterigmata. Basidia with basidiospores can form either on the mycelium or on the surface of or inside fruiting bodies. Fruiting bodies are formed by densely intertwined hyphae of the dikaryotic mycelium and vary in shape, color, and consistency. They bear a spore-bearing layer called the hymenium, consisting of basidia, sterigmata, and paraphyses. The surface of the fruiting body that bears the hymenium is called the hymenophore. It can be smooth, folded, lamellate, dentate, or tubular.

Depending on their structure, basidia can be unicellular, tetracellular, or complex. Unicellular basidia are club-shaped and called holobasidia; tetracellular ones are phragmobasidia; and complex ones are heterobasidia, which consist of a lower sterile part (hypobasidium) and an upper part (epibasidium) that bears four basidiospores. Asexual reproduction is carried out via conidia. Vegetatively, these fungi reproduce through fragments of mycelium or chlamydospores.

Based on their development type and basidial structure within the phylum Basidiomycota (Basidiomycota), three classes are distinguished: Basidiomycetes, Urediniomycetes, and Ustilaginomycetes.

The class Basidiomycetes (Basidiomycetes) is characterized by unicellular basidia, though heterobasidia form less frequently. It is divided into two main subclasses: Agaricomycetidae and Tremellomycetidae. Agaricomycetidae include such representatives as the dry rot fungus, tinder fungus, chanterelle, annosum root rot, fly agaric, russula, milk-cap, mushroom, honey fungus, bolete, bay bolete, Satan's bolete, puffball (Bovista, Calvatia, Lycoperdon), earthball, and stinkhorn. Regarding their mode of nutrition, they are mostly saprotrophs or mycorrhizal symbionts.

Among parasitic species, the most common are species of the genus Fomes (tinder fungi), which parasitize woody plants. In the tree trunk, they develop a perennial mycelium that destroys the plant's Vascular System (xylem or wood), causing top-dryness; a hollow forms inside the trunk, making these trees susceptible to windthrow and windbreak. Hard, perennial fruiting bodies form on the trunk surface, whose hymenophores produce basidiospores. Upon landing on a tree wound, basidiospores germinate into mycelium. Other notable parasites include the annosum root rot and oak mazegill.

The Agaricales include numerous edible mushrooms: the porcini, chanterelle, birch bolete, orange-cap boletus, russula, milk-cap, etc. There are also many poisonous fungi: the death cap, fly agaric, devil's bolete, false honey fungus, false chanterelle, etc.

Tremellomycetoid fungi, which differ from agarics by having complex basidia, are predominantly saprotrophs and occasionally fungal parasites. Their practical significance is negligible.

The class Urediniomycetes (Uredinomycetes), or rust fungi, possess tetracellular basidia and parasitize virtually all cultivated plant species and most wild ones. As a rule, most of them have a complex developmental cycle spanning two host plants with multiple sporulation stages. Conidiospores, often called spermatia or pycniospores, develop on the primary haploid mycelium, whereas aeciospores, urediniospores, and teliospores develop on the dikaryotic secondary mycelium, followed by haploid basidiospores on the basidium. The presence of functionally distinct spores in a fungus is termed pleomorphism. Diseased plants can be identified by brown spots or stripes on their stems or leaves, hence the name rust fungi. Parasites of the genus Puccinia are most commonly found on agricultural crops. The developmental cycle of Puccinia graminis is described in detail in the corresponding laboratory work. Schematically, the Life Cycle of a heteroecious rust fungus developing on two host plants can be described as follows. A basidiospore landing on the leaf of an alternate host germinates into a primary haploid mycelium, which produces the first sporulation stage on the upper leaf surface—pycnia, appearing as flask-like structures filled with pycniospores. Pycnia secrete a sweet liquid that attracts insects, which transfer spores from one pycnium to another. Pycnial spores are physiologically dissimilar. When a spore of one mating type enters a pycnium of the opposite mating type, plasmogamy occurs, initiating the dikaryophytic stage of the fungus and forming a secondary dikaryotic mycelium. This mycelium then forms receptacles for binucleate spores—aecia enclosed by a peridium—on the lower leaf surface. Aeciospores form within the aecia and are released upon the breakdown of the peridium. Aeciospores are carried by the wind to the primary host plant, where they germinate into a dikaryotic mycelium that produces the summer spores of the fungus, or urediniospores. These are stalked, binucleate spores that easily detach and scatter, causing mass plant infection. Toward the end of the growing season, bicellular teliospores with thick walls, a diploid nucleus, and nutrient reserves form on the mycelium. In spring, each teliospore cell germinates into a tetracellular phragmobasidium. Each of these cells produces a basidiospore, which is then transferred back to the alternate host plant.

Rust fungi cause severe damage to agriculture and forestry; grain losses alone during mass outbreaks can reach millions of tons annually.

The class Ustilaginomycetes (Ustilaginomycetes), or smut fungi, is represented by parasitic fungi that do not form fruiting bodies and feature tetracellular basidia. These are also parasitic fungi whose dikaryophytic mycelium develops mostly inside plant organs and destroys them using appressoria within the host cells. They predominantly infect cereals: wheat, corn, and oats. During the plant's vegetation period, the mycelium breaks down into dark, thick-walled chlamydospores that resemble soot, giving the class its name. Based on external appearance, one distinguishes covered smut, loose smut, and common corn smut.

Chlamydospores, or teliospores, serve as the primary means of plant infection and retain their germination capacity for 20–25 years. Upon landing on a favorable substrate, a dikaryophytic chlamydospore undergoes karyogamy, becoming diploid. The diploid cell germinates into a basidium with four basidiospores. Subsequently, the haploid basidiospores, or the primary mycelium they have germinated into, fuse to form a secondary dikaryophytic mycelium. It is this mycelium that invades the host Tissues and proliferates between the cells of the infected plants. During the growing season, the secondary mycelium breaks down into chlamydospores, which can overwinter in the soil or adhere to healthy cereal grains, thereby surviving.

Smut fungi cause substantial agricultural damage; effective control measures include pre-planting seed dressing, seed heat Treatment, and the breeding of smut-resistant varieties.

5.5.5. Group of Anamorphic or Mitosporic Fungi (Deuteromycetes, or Fungi Imperfecti) (Deuteromycoｔa)

These are higher fungi characterized by a well-developed, multicellular, septate, haploid mycelium. They reproduce exclusively asexually via conidia. They do not undergo sexual reproduction or produce its characteristic products found in higher fungi—asci and basidia—hence they are referred to as imperfect, anamorphic, or asexual fungi. Due to the mitotic mode of conidiospore Cell Formation, they are also termed mitosporic. This group represents a formal rather than a taxonomic unit, as the discovery of ascomycetous or basidiomycetous sporulation allows their Classification into Ascomycota or Basidiomycota. Conidiophores occur singly or in groups forming coremia, sporodochia, acervuli, or pycnidia.

Among anamorphic fungi, three orders are distinguished: Hyphomycetales, Melanconiales, and Sphaeropsidales. The order Hyphomycetales is characterized by single conidiophores or those aggregated into coremia and sporodochia, encompassing genera such as Aspergillus, Penicillium, Fusarium, Verticillium, Cladosporium, and Helminthosporium. The order Melanconiales is characterized by group sporulation in the form of an acervulus, including the genus Gloeosporium. The order Sphaeropsidales unites fungi with conidiophores enclosed within pycnidia, featuring genera such as Septoria, Phoma, Phyllosticta, and Ascochyta.

The vast majority of these fungi are saprotrophs, whereas parasitic forms—such as those of the genus Fusarium—cause diseases like fusariosis in legumes, flax, and corn cobs; representatives of the genus Verticillium, developing within the vascular systems of sunflower, hop, potato, and tomato leaves, cause vascular wilt; and species of the genus Cercospora cause leaf and stem spot diseases in many cultivated plants. Some fungi spoil fodder or cause rots.

Fungi of the genus Penicillium (green mold) are used to produce Antibiotics and in cheesemaking.