Ascomycota : Structure,Reproduction and Economic Importance

In this article we will discuss about (1) The Structure (2) Reproduction (3) Economic Importance

The Ascomycota are morphologically diverse. The group includes organisms from unicellular yeasts to complex cup fungi. There are 2000 identified genera and 30,000 species of Ascomycota. The unifying characteristic among these diverse groups is the presence of a reproductive structure known as the ascus, though in some cases it has a reduced role in the life cycle. As a group, they are economically important. Many are tree diseases, such as dutch elm disease and apple blights. The yeasts are used to produce alcoholic beverages and breads. The mold Penacillium is used to produce the anit-biotic penicillin.

(1) Structure

Like basidiomycota, most ascomycota sprout from spores into hapliod mycelia. These mycelia can produce two types of reproductive structures. First, they can produce conidiophores for asexual reproduction. Conidiaphores may simply branch off from the mycelia or they may be formed in fruiting bodies. Secondly, ascomycota produce structures for sexual reproduction called gametangia. These structures are either male or female. The male gametangia may be anything from a detached cell (called a spermatium) to a differentiated region called an antheridium. The female structure is always a differentiated region known as the ascogonium. Many Ascomycota form a fruiting body, or ascoma, similar to that of the Basidiomycota, but with an important difference. The ascomycota fruiting body is composed mainly of entangled monokaryotic hyphae from the male and female mycelia rather than of dikaryotic hyphae formed from the joining of hyphae from the two mycelia, as in the basidiomycota. The only dikaryotic structures in the fruiting body are those produced by the gametangia after plasmogamy.

The exceptions to the above discussion of structure are the unicellular ascomycota or yeasts. These organisms are non-motile single cells with chitinous cell walls that earn them classification as fungi. Though they mainly reproduce by budding and fission, yeasts also engage in sexual reproduction that results in the production of an ascus, placing them in the Ascomycota. Most varieties of yeast do not form multicellular filiments like the mycelia and hyphae of other fungi, though they do live in massive groupings called colonies.

(2) Reproduction

Like all fungi, Ascomycota can undergo both asexual and sexual reproduction.

Asexual Reproduction

Asexual reproduction among the different groups of fungi are very similar. Like Basidiomycota, Ascomycota reproduce asexually through budding or the formation of conidia.

Sexual Reproduction

Sexual reproduction in the Ascomycota differs from that in the Basidiomycota and Zygomycota because Ascomycota have male and female gametangia in their haploid stage. These structures, discussed in Heading , form on the mycelia. Plasmogamy, or the transfer of cytoplasm and nuclei, takes place when a part of the ascogonium, the trichogyne, fuses with the antheridium. This produces a binucleate, dikaryotic condition in the ascogonium. This phase is prolonged and a series of dikaryotic cells called an ascogonius hypha is produced. At the tip of this hypha, karyogamy or nuclear fussion takes place, resulting in the formation of a diploid ascus. Within this structure, the diploid nucleus undergoes meiosis, producing four haploid nuclei. These nuclei then undergo mitosis to form eight haploid ascospores. Notice that this is twice as many spores as produced in the basidium.

(3) Economic Importance

There are several members of Ascomycetes which are economically important. The members have useful as well as harmful effects to the man kind. Some these economic roles of these members are;

Beneficial aspects of fungi:

• Productions of beverages such as the beers, malt tonics are fermented from the malts by the fungus Saccharomyces cerevisiae.
• Productions of alcohol are mostly done with the help of the fungus Saccharomyces cerevisiae and Saccharomyces ellipsoideus. These fungi are used to ferment the starch and sugar to prepare alcohol.
• Vinegars are produced from the fruits, malts etc. with the help of the fungus Saccharomyces cerevisiae.
• Production of antibiotics like Penicillin is also done with the aid of the fungus like the Penicillium notatum and Penicillium chrysogenum. The Aspergillus species are also widely used in the preparation of the antibiotics.
• The Penicillium roqueforti and Penicillium camemberti are used are used for flavoring the cheese.
• Some Penicillium species are used in the production of the citric acid, oxalic acid, fumaric acid and gluconic acids etc.
• Yeast is widely used in the baking industries.
• Yeast is also used in the genetic researches also.
• This fungus also involves the edible groups like morels and truffles which are rich in the proteins, vitamins, fats and carbohydrates.

Harmful aspects of fungi:

• Some of the species of yeast are responsible for the spoilage of the food items like cheese, tomato products etc.
• Nematospora species causes various diseases in tomato, beans and cotton.
• Aspergillus species cause spoilage of food stuffs and deterioration of leather goods and fabrics.
• Penicillium expansum causes spoilage of apples, grapes and peas in storage.
• The powdery mildew of peas is caused by Erysiphe polygoni.
• The ergot of cereals is caused by the fungal species Claviceps purpurea.
• Candida species causes candidiasis in human beings.
• Taphrina maculans causes the leaf spot in turmeric plants.