The fungi are a group of Eukaryotic microorganisms that lack chlorophyll, fungi can not prepare their own food so they are heterotrophic.
They either obtained their food from dead organic matter as saprophytes or obtained food from the bodies of living plants and animals as parasites .
Fungi have some distinctive features which set them well apart from both plants and animals.
? Fungi differ from plants in the following features;
1. The cell wall of most fungi consist of chitin rather than cellulose as in plants. Sometimes chitin and cellulose both are present simultaneously .
2. Fungi are usually multicellular but are not differentiated into roots, stem and leaves like plants.
3. Fungi stored food in the form of glycogen rather than glucose as plants do.
4. Due to lack of cholorophyll, fungi are unable to synthesize their own food and are, therefore, heterotrophic.
? Fungi differ from animals in the following features:
1. Unlike animals, the fungi can not injest solid food materials. They obtain their food from the surrounding media in soluble form in a manner similar to prokaryotes.
2. Fungi show a distinctive growth pattern. In most of these organisms, every part of mycelium have the potential for growth.
3. Fungi have chemically and morphologically differentiated rigid cell wall during all stages of growth , usually made of chitin while animals lack it.
From all above discussion it is clear that fungi are different from Plants and animals and scientists agree upon this, that they merit a kingdom of their own.
The science which deals with fungi is known as mycology. The fungi are a diverse group of organisms with more than 1,00,000 species with several more yet to be described.
Fungi are of great economic importance.
? A large number of fungi destroy our food resources
? Very many of them cause diseases of plants , animals and man.
? Some of them are utilized as food.
? Some are used in medicines.
? Some are used in the production of chemicals and other industrial processes.
The common representatives are Mashrooms, Toadstools, puff-balls, mildews, rusts, molds, smuts and other many plant pathogens.
Morphology of Fungi:
? Microscopic structures:
Most fungi grow as hyphae, which are cylindrical, thread-like structures 2–10 µm in diameter and up to several centimeters in length.
Hyphae grow at their tips (apices), new hyphae are typically formed by emergence of new tips along existing hyphae by a process called branching, or occasionally growing hyphal tips fork, giving rise to two parallel-growing hyphae.
Hyphae also sometimes fuse when they come into contact, a process called hyphal fusion (or anastamosis). These growth processes lead to the development of a mycelium, an interconnected network of hyphae.
Hyphae can be either septate or coenocytic. Septate hyphae are divided into compartments separated by cross walls (internal cell walls, called septa, that are formed at right angles to the cell wall giving the hypha its shape), with each compartment containing one or more nuclei; coenocytic hyphae are not compartmentalized. Septa have pores that allow cytoplasm, organelles, and sometimes nuclei to pass through; an example is the dolipore septum in fungi of the phylum Basidiomycota. Coenocytic hyphae are in essence multinucleate supercells.
Many species have developed specialized hyphal structures for nutrient uptake from living hosts; examples include haustoria in plant-parasitic species of most fungal phyla, and arbuscules of several mycorrhizal fungi, which penetrate into the host cells to consume nutrients.
Although fungi are opisthokonts—a grouping of evolutionarily related organisms broadly characterized by a single posterior flagellum—all phyla except for the chytrids have lost their posterior flagella. Fungi are unusual among the eukaryotes in having a cell wall that, in addition to glucans (e.g., ?-1,3-glucan) and other typical components, also contains the biopolymer chitin.
Fig. 1.4An environmental isolate of Penicillium hypha conidiophore phialide conidia septa
? Macroscopic structures:
Fungal mycelia can become visible to the naked eye, for example, on various surfaces and substrates, such as damp walls and spoiled food, where they are commonly called molds. Mycelia grown on solid agar media in laboratory petri dishes are usually referred to as colonies. These colonies can exhibit growth shapes and colors (due to spores or pigmentation) that can be used as diagnostic features in the identification of species or groups. Some individual fungal colonies can reach extraordinary dimensions and ages as in the case of a clonal colony of Armillaria solidipes, which extends over an area of more than 900 ha (3.5 square miles), with an estimated age of nearly 9,000 years.
The apothecium—a specialized structure important in sexual reproduction in the ascomycetes—is a cup-shaped fruit body that is often macroscopic and holds the hymenium, a layer of tissue containing the spore-bearing cells.
The fruit bodies of the basidiomycetes (basidiocarps) and some ascomycetes can sometimes grow very large, and many are well known as mushrooms.
Fig 1.5Armillaria solidipes
Importance of Fungi:
Fungi are one of the most important groups of organisms on the planet. This is easy to overlook, given their largely hidden, unseen actions and growth. They are important in an enormous variety of ways.
? Recycling :
Fungi, together with bacteria, are responsible for most of the recycling which returns dead material to the soil in a form in which it can be reused.
Without fungi, these recycling activities would be seriously reduced. We would effectively be lost under piles many metres thick, of dead plant and animal remains.
? Mycorrhizae and plant growth:
Fungi are vitally important for the good growth of most plants, including crops, through the development of mycorrhizal associations.
As plants are at the base of most food chains, if their growth was limited, all animal life, including human, would be seriously reduced through starvation.
Fungi are also important directly as food for humans. Many mushrooms are edible and different species are cultivated for sale worldwide. While this is a very small proportion of the actual food that we eat, fungi are also widely used in the production of many foods and drinks. These include cheeses, beer and wine, bread, some cakes etc. While a great many wild fungi are edible, it can be difficult to correctly identify them. Some mushrooms are deadly if they are eaten. Fungi with names such as ‘Destroying Angel’ and ‘Death Cap’ give us some indication that it would not be a terribly good idea to eat them! In some countries, collecting wild mushrooms to eat is a popular activity. It is always wise to be totally sure that what you have collected is edible and not a poisonous look-a-like.
Penicillin, perhaps the most famous of all antibiotic drugs, is derived from a common fungus called Penicillium. Many other fungi also produce antibiotic substances, which are now widely used to control diseases in human and animal populations. The discovery of antibiotics revolutionized health care worldwide.
Some fungi which parasitise caterpillars have also been traditionally used as medicines. The Chinese have used a particular caterpillar fungus as a tonic for hundreds of years. Certain chemical compounds isolated from the fungus may prove to be useful treatments for certain types of cancer.
A fungus which parasitises Rye crops causes a disease known as Ergot. The fungus can occur on a variety of grasses. It produces small hard structures, known as sclerotia. These sclerotia can cause poisoning in humans and animals which have eaten infected material. However, these same sclerotia are also the source of a powerful and important drug which has uses in childbirth.
Fungi such as the Chinese caterpillar fungus, which parasitise insects, can be extremely useful for controlling insect pests of crops.
The spores of the fungi are sprayed on the crop pests. Fungi have been used to control Colorado potato beetles, which can devastate potato crops. Spittlebugs, leaf hoppers and citrus rust mites are some of the other insect pests which have been controlled using fungi. This method is generally cheaper and less damaging to the environment than using chemical pesticides.
? Crop diseases:
• Fungal parasites may be useful in biocontrol, but they can also have enormous negative consequences for crop production. Some fungi are parasites of plants. Most of our common crop plants are susceptible to fungal attack of one kind or another. Spore production and dispersal is enormously efficient in fungi and plants of the same species crowded together in fields are ripe for attack. Fungal diseases can on occasion result in the loss of entire crops if they are not treated with antifungal agents.
? Animal Diseases:
Fungi can also parasitise domestic animals causing diseases, but this is not usually a major economic problem. A wide range of fungi also live on and in humans, but most coexist harmlessly. Athletes foot and Candida infections are examples of human fungal infections.
? Food spoilage:
It has already been noted that fungi play a major role in recycling organic material. The fungi which make our bread and jam go mouldy are only recycling organic matter, even though in this case, we would prefer that it didn’t happen! Fungal damage can be responsible for large losses of stored food, particularly food which contains any moisture. Dry grains can usually be stored successfully, but the minute they become damp, moulds are likely to render them inedible. This is obviously a problem where large quantities of food are being produced seasonally and then require storage until they are needed.