What type of spores are produced by the fungus pictures at the right

The budding yeasts reproduce asexually by budding off a smaller daughter cell; the resulting cells may sometimes stick together as a short chain or pseudohypha Figure 1. Candida albicans is a common yeast that forms pseudohyphae; it is associated with various infections in humans, including vaginal yeast infections, oral thrush, and candidiasis of the skin. Some fungi are dimorphic, having more than one appearance during their life cycle. These dimorphic fungi may be able to appear as yeasts or molds, which can be important for infectivity.

This ability helps dimorphic fungi to survive in diverse environments. Histoplasma capsulatum , the pathogen that causes histoplasmosis , a lung infection, is an example of a dimorphic fungus Figure 2. Figure 2. Histoplasma capsulatum is a dimorphic fungus that grows in soil exposed to bird feces or bat feces guano top left.

It can change forms to survive at different temperatures. There are notable unique features in fungal cell walls and membranes. Fungal cell walls contain chitin , as opposed to the cellulose found in the cell walls of plants and many protists. Additionally, whereas animals have cholesterol in their cell membranes, fungal cell membranes have different sterols called ergosterols.

Ergosterols are often exploited as targets for antifungal drugs. Fungal life cycles are unique and complex. Fungi reproduce sexually either through cross- or self-fertilization. Haploid fungi form hyphae that have gametes at the tips. Later, the nuclei fuse in an event called karyogamy to create a diploid zygote.

The zygote undergoes meiosis to form spores that germinate to start the haploid stage, which eventually creates more haploid mycelia Figure 3. Depending on the taxonomic group, these sexually produced spores are known as zygospores in Zygomycota , ascospores in Ascomycota , or basidiospores in Basidiomycota Figure 4. Fungi may also exhibit asexual reproduction by mitosis, mitosis with budding, fragmentation of hyphae, and formation of asexual spores by mitosis. These spores are specialized cells that, depending on the organism, may have unique characteristics for survival, reproduction, and dispersal.

Fungi exhibit several types of asexual spores and these can be important in classification. Figure 3. Click for a larger image. Zygomycetes have sexual and asexual life cycles. The fungi are very diverse, comprising seven major groups. Not all of the seven groups contain pathogens. Some of these groups are generally associated with plants and include plant pathogens.

For example, Urediniomycetes and Ustilagomycetes include the plant rusts and smuts , respectively. These form reddish or dark masses, respectively, on plants as rusts red or smuts dark.

Some species have substantial economic impact because of their ability to reduce crop yields. Glomeromycota includes the mycorrhizal fungi , important symbionts with plant roots that can promote plant growth by acting like an extended root system.

The Glomeromycota are obligate symbionts, meaning that they can only survive when associated with plant roots; the fungi receive carbohydrates from the plant and the plant benefits from the increased ability to take up nutrients and minerals from the soil. The Chytridiomycetes chytrids are small fungi, but are extremely ecologically important.

Chytrids are generally aquatic and have flagellated, motile gametes; specific types are implicated in amphibian declines around the world. Because of their medical importance, we will focus on Zygomycota, Ascomycota, Basidiomycota, and Microsporidia.

Figure 9 summarizes the characteristics of these medically important groups of fungi. The Zygomycota zygomycetes are mainly saprophytes with coenocytic hyphae and haploid nuclei. They use sporangiospores for asexual reproduction. Zygomycetes have a thallus of coenocytic hyphae in which the nuclei are haploid when the organism is in the vegetative stage.

The fungi usually reproduce asexually by producing sporangiospores Figure. The black tips of bread mold are the swollen sporangia packed with black spores Figure. When spores land on a suitable substrate, they germinate and produce a new mycelium.

Sexual reproduction starts when environmental conditions become unfavorable. Each zygospore can contain several diploid nuclei. The developing diploid zygospores have thick coats that protect them from desiccation and other hazards. They may remain dormant until environmental conditions are favorable. When the zygospore germinates, it undergoes meiosis and produces haploid spores, which will, in turn, grow into a new organism.

Rhizopus spores. Asexual sporangia grow at the end of stalks, which appear as a white fuzz seen on this bread mold, Rhizopus stolonifer. The black tips b of bread mold are the spore-containing sporangia. Filamentous ascomycetes produce hyphae divided by perforated septa, allowing streaming of cytoplasm from one cell to another. Conidia and asci, which are used respectively for asexual and sexual reproduction, are usually separated from the vegetative hyphae by blocked non-perforated septa.

Many ascomycetes are of commercial importance. Some play a beneficial role for humanity, such as the yeasts used in baking, brewing, and wine fermentation, and directly as food delicacies such as truffles and morels. Aspergillus oryzae is used in the fermentation of rice to produce sake.

Other ascomycetes parasitize plants and animals, including humans. For example, fungal pneumonia poses a significant threat to AIDS patients who have a compromised immune system. Ascomycetes not only infest and destroy crops directly; they also produce poisonous secondary metabolites that make crops unfit for consumption. Asexual reproduction is frequent and involves the production of conidiophores that release haploid conidiospores Figure.

Sexual reproduction starts with the development of special hyphae from either one of two types of mating strains Figure. At fertilization, the antheridium and the ascogonium combine in plasmogamy, without nuclear fusion.

In each ascus, two haploid nuclei fuse in karyogamy. Thousands of asci fill a fruiting body called the ascocarp. The diploid nucleus in each ascus gives rise to haploid nuclei by meiosis, and spore walls form around each nucleus. The spores in each ascus contain the meiotic products of a single diploid nucleus. The ascospores are then released, germinate, and form hyphae that are disseminated in the environment and start new mycelia Figure.

Which of the following statements is true? Basidiomycota: The Club Fungi The fungi in the Phylum Basidiomycota are easily recognizable under a light microscope by their club-shaped fruiting bodies called basidia singular, basidium , which are the swollen terminal cells of hyphae.

The basidia, which are the reproductive organs of these fungi, are often contained within the familiar mushroom, commonly seen in fields after rain, on the supermarket shelves, and growing on your lawn Figure. The gills are actually compacted hyphae on which the basidia are borne.

This group also includes shelf fungi, which cling to the bark of trees like small shelves. In addition, the basidiomycota include smuts and rusts, which are important plant pathogens.

Most edible fungi belong to the Phylum Basidiomycota; however, some basidiomycota are inedible and produce deadly toxins. For example, Cryptococcus neoformans causes severe respiratory illness. The infamous death cap mushroom Amanita phalloides is related to the fly agaric seen at the beginning of the previous section.

The lifecycle of basidiomycetes includes alternation of generations Figure. Most fungi are haploid through most of their life cycles, but the basidiomycetes produce both haploid and dikaryotic mycelia, with the dikaryotic phase being dominant.

Note: The dikaryotic phase is technically not diploid, since the nuclei remain unfused until shortly before spore production. At this stage, spores are disseminated into the environment. Learning Objectives Describe the mechanisms of sexual and asexual reproduction in fungi. Key Points New colonies of fungi can grow from the fragmentation of hyphae. During budding, a bulge forms on the side of the cell; the bud ultimately detaches after the nucleus divides mitotically.

Asexual spores are genetically identical to the parent and may be released either outside or within a special reproductive sac called a sporangium. Adverse environmental conditions often cause sexual reproduction in fungi. Mycelium can either be homothallic or heterothallic when reproducing sexually. Fungal sexual reproduction includes the following three stages: plasmogamy, karyogamy, and gametangia.

Key Terms homothallic : male and female reproductive structures are present in the same plant or fungal mycelium gametangium : an organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi, and the gametophytes of plants spore : a reproductive particle, usually a single cell, released by a fungus, alga, or plant that may germinate into another sporangium : a case, capsule, or container in which spores are produced by an organism karyogamy : the fusion of two nuclei within a cell plasmogamy : stage of sexual reproduction joining the cytoplasm of two parent mycelia without the fusion of nuclei.

Asexual Reproduction Fungi reproduce asexually by fragmentation, budding, or producing spores. The organism depicted is a Mucor sp. As a result, the thresholds for symptoms will also vary. However, thresholds have only been ascertained for Alternaria and Cladosporium so far. The calendars have been produced by averaging 5 years of data collected in Worcester. Worcester is located in the centre West of the country and receives high amounts of pollen and spores due to very suitable weather and sources.

Although the trends shown will be similar for much of the country, the average amounts will tend to be lower in western coastal regions and mountainous areas.

The spore seasons in Northern Ireland, Scotland and the far North England will also start a few days to two weeks later than in the more southerly regions. A weekly spore forecast for spores is available here.

The peak average monthly total occurs in August spores then in September high counts continue but go into decline. November to March are very low for this type. In June, the average monthly total reaches ,, in July , and in August , The spores go into decline in mid-September, with just occasional high days during warm weather.

October to May are very low for this type. The peak period is well defined, starting in late June and reaching peak period in July, which continues through August with a monthly average peak total of 35, spores. There may be a few high days in early September then the risk drops to very low. The year starts with a high risk for these types with a total monthly average of 1, spores in January and 1, in February.

Spores continue to be airborne during Spring and early Summer but possibly below the levels needed to trigger symptoms, although studies show that A. From mid-August the risk starts to rise again and people often report symptoms during warm, humid conditions in late August, September and October, with the peak reaching an average of 1, spores in October.

Although the spore levels continue to be high during November and December, few people report symptoms, so it is likely that the types occurring during these months are less allergenic. The peak monthly total occurs in September for this type at 32, spores, after gradually increasing over the summer months.

October is also a peak month, with a similar total. The risk drops rapidly down to low by December. January through to early June are low for these spores. January to early June remain low for this type, with the increase starting during warm weather from mid-June.

The peak monthly total occurs in August at 1, spores, September sees a similar high at 1, spores and then the season goes into decline through October, returning to low in November and December.

Leptosphaeria or Phoma fungi mainly occur in crop-growing areas especially where one of their major hosts, oilseed rape, is grown.

The spores are liberated during or after rain and are rarely present during dry weather. Spores can be emitted at any time of year during rainfall but the levels really start to increase during wet weather in April and May, continuing at a high risk until late October or early November.

Very dry months have lower levels of Leptosphaeria compared to the average. Aerobiologia, 32 4 : In the Spring, most spore types are at low levels, apart from Pleospora. Cladosporium and Tilletiopsis can start increasing in May if the weather is warm and dry. The spore risk starts to rise in mid-June with the increase in temperatures.