24.2 Classifications of Fungi

• Sexual reproduction can occur in response to adverse environmental conditions.
• Two types of males are produced during sexual reproduction.

• There are many variations in sexual reproduction.
• Meiosis takes place in the gametangia, in which gametes of different types are generated.
• At this point, the environment is affected by the spores.

• You can review the characteristics of fungi by visiting the interactive site from Wisconsinonline.

• By the end of this section, you will be able to identify and classify the five major phyla of the kingdom Fungi.
• Polyphyletic, unrelated fungi that reproduce without a sexual cycle, were placed for convenience in a sixth group because they looked similar.
• Most mycologists have stopped this practice.
• There are new and different relationships among the various categories of fungi as a result of the rapid advances in the field of biology.

• The five true phyla of fungi are the chytridiomycota, the conjugated fungi, the Ascomycota, the Basidiomycota, and the recently described Phy.

• "-mycetes" is used informally to refer to all members of the phylum, while "-mycota" is used formally to designate a class.

• The first recognizable chytrids appeared more than 500 million years ago.
• One group of chytrids has both the cell wall and the cell wall alone.
• Most chytrids are unicellular, but a few have no septa between cells.
• Only the chytrids have flagella.
• They produce both gametes and diploid zoospores that swim with a single flagellum.
• The male and female gametes are flagellated.

• The ecological habitat and cell structure of chytrids are similar to protists.
• Some species of chytrids live on land.
• Some species thrive as parasites on plants.
• The Allomyces is an experimental species.
• The reproductive cycle includes both asexual and sexual phases.
• Allomyces produces diploid or haploid flagellated zoospores.

• The chytrid Batrachochytrium dendrobatidis is seen in these light micrographs as transparent spheres growing on a freshwater arthropod and a algae.
• The decline and extinction of many species of salamanders is caused by the chytrid.
• The bread mold, Rhizopus stolonifer, can be found on breads, fruits, and vegetables.
• Most species are saprobes, living off decaying organic material.
• There is a considerable commercial role for zygomycetes.
• Some species of Rhizopus have intermediates in the synthesis of semisynthetic steroid hormones.

• The thallus of coenocytic hyphae of zygomycetes is haploid when the organism is in the vegetative stage.

• The fungi usually reproduce asexually.
• The black tips of bread mold are swollen with black spores.

• Sexual reproduction begins when the environment becomes unfavorable.
• Two opposing strains must be in close proximity to each other for gametangia to occur.
• There are several diploid nuclei in the zygospore.
• They may not be active until environmental conditions are favorable.
• When the zygospore begins to grow, it undergoes meiosis and produces haploid spores, which will in turn, grow into a new organisms.
• conjugated fungi is the name of this form of sexual reproduction in fungi, which differs from the other forms of sexual reproduction.

• There are sexual and asexual phases in zygomycetes.
• In the asexual phase, the haploid sporangia is produced.
• In the sexual phase, plus and minus haploid mating types conjugate.
• A diploid zygote is produced by Karyogamy.
• The next generation of haploid spores can be formed by diploid cells in the zygote.

• Asexual sporangia grow at the end of stalks, which look like white fuzz on this bread mold.
• The bread mold has black tips.
• The ascomycetes allow for streaming of the cytoplasm from one cell to another.
• Conidia and asci are usually separated from the hyphae by septa.
• Commercial ascomycetes are important.
• The yeasts used in baking, beer, wine, and food are some of the beneficial ones.
• In the production of sake, Aspergillus oryzae is used.
• Plants and animals are vulnerable to ascomycetes.
• AIDS patients who have a compromised immune system are at risk of being victims of fungal pneumonia.
• Ascomycetes produce poisonous secondary metabolites that make crops unsuitable for consumption.

• Asexual reproduction involves the production of conidiophores that release haploid conidiospores.

• Sexual reproduction begins with the development of special hyphae from either of the two types of strains.

• The "female" strain develops an ascogonium while the "male" strain produces an antheridium.
• The diploid nucleus in each ascus gives rise to haploid nuclei.
• The meiotic products of a single diploid nucleus are contained in each ascus.
• New mycelia can be started by the ascospores being released, germinating, and forming hyphae that are disseminated in the environment.

• The production of asci during the sexual phase is a part of the lifecycle of an ascomycete.
• Four of the four nuclei produced by meiosis divide into eight haploid ascospores.
• The life cycle in Ascomycetes is dominated by the haploid phase.

• Eight ascospores are formed by a dikaryotic ascus that forms in the ascocarp.

• Eight ascospores are formed by a diploid ascus that forms in the ascocarp.

• The bright field light micrograph shows ascospores being released from asci.
• The basidia, which are the reproductive organs of these fungi, are often contained within the familiar mushroom, which is commonly seen in fields after rain, on the supermarket shelves, and growing on your lawn.
• The basidiomycetes are sometimes referred to as "gill fungi" because of the structures on the underside of the cap.
• The basidia are on the hyphae of the gills.
• Shelf fungi cling to the bark of trees like small shelves.
• Smuts and rusts are important plant pathogens and are included in the basidiomycota.
• Some basidiomycota are inedible and can produce deadly toxins.
• Severe respiratory illness can be caused by Cryptococcus neoformans.
• The fly agaric seen at the beginning of the previous section is related to the death cap mushroom.

• The fairy ring fungus has a scientific name.
• As it grows, the mycelium depletes the soil of nitrogen, causing the mycelia to grow away from the center and leading to the "fairy ring" of fruiting bodies where there is adequate soil nitrogen.
• The basidiomycetes produce both haploid and dikaryotic mycelia, with the dikaryotic phase being dominant.

• Sexual spores are more common than asexual ones in the basidiomycetes.
• The sexual spores are found in the club-shaped basidium.
• In the basidium, the nucleus of two different strains of marriage give rise to a diploid zygote.
• The haploid nuclei migrate into four different chambers and become basidiospores.

• A primary mycelium is the mycelium that results.
• A secondary mycelium can be created by combining mycelia of different strains.
• The basidiomycete life cycle has a dominant dikaryotic stage.
• Each cell in this mycelium has two haploid nuclei, which will not be fused until the basidium is formed.
• The developing basidia are on the gills of the basidiocarp.

• There are different generations of basidiomycete with haploid and dikaryotic mycelia.

• The primary mycelia form a dikaryotic secondary mycelium, which is the main stage of the life cycle.

• Four basidiocarps are formed by a basidium, the fruiting body of a mushroom- producing fungus.

• Four basidiospores were the result of the plasmogamy step.

• Some of the members in this group are classified as belonging to the Ascomycota or the Basidiomycota.