Meaning and Definitions of Fungi:
What is Fungi?
Fungi are eukaryotic organisms that include microorganisms such as yeasts, moulds and mushrooms. These organisms are classified under kingdom fungi.
The organisms found in Kingdom fungi contain a cell wall and are omnipresent. They are classified as heterotrophs among the living organisms.
Fungi (singular fungus — mushroom, from Greek) are chlorophyll-less thallophytic plant. Due to absence of chlorophyll, they are heterophytes i.e., depend on others for food. They grow in various habitats and show much diversity in their structure, physiology and reproduction. They developed long back in the geological time scale.
Their existence was found from fossil records of Pre-Cambrian period. Information from ancient literature indicates that the fungi were used as food by human beings. At present, the fungi are used in medicine and also as food in addition to other aspects. The fungi cause diseases of crops (spots, rusts and smuts etc.) and on human beings (Aspergillosis, Blastomycosis etc.).
Some of the plant diseases like late blight of potato (c.o. Phytophthora infestans) and brown spot of rice (c.o. Helminthosporium oryzae) caused famine in Ireland (1845) and in West Bengal (India) (1943), respectively.
More than 5,000 genera and 50,000 species of fungi have been recorded, but their number may be much more than the actual record. The subject which deals with fungi is known as Mycology (mykes — mushroom; logos— study) and the concerned scientist is called mycologist.
The various definitions of fungi as proposed by mycologists are:
1. Alexopoulos (1962):
Alexopoulos (1962) defined fungi as “nucleated, spore-bearing, achlorophyllous organisms which generally reproduce sexually and asexually and whose usually filamentous, branched somatic structures are typically surrounded by cell walls containing cellulose or chitin or both”.
2. Alexopoulos and Mims (1979):
Alexopoulos and Mims (1979) defined fungi as eukaryotic spore bearing, achlorophyllous organisms that generally reproduce sexually and asexually, and whose usually filamentous, branched somatic structures are typically surrounded by cell walls containing chitin or cellulose, or both of these substances, together with many other complex organic molecules”.
Characteristics of Fungi
Following are the important characteristics of fungi:
- Fungi are eukaryotic, non-vascular, non-motile and heterotrophic organisms.
- They may be unicellular or filamentous.
- They reproduce by means of spores.
- Fungi exhibit the phenomenon of alternation of generation.
- Fungi lack chlorophyll and hence cannot perform photosynthesis.
- Fungi store their food in the form of starch.
- Biosynthesis of chitin occurs in fungi.
- The nuclei of the fungi are very small.
- The fungi have no embryonic stage. They develop from the spores.
- The mode of reproduction is sexual or asexual.
- Some fungi are parasitic and can infect the host.
- Fungi produce a chemical called pheromone which leads to sexual reproduction in fungi.
- Examples include mushrooms, moulds and yeast.
Occurrence of Fungi
Fungi are one of the most important groups of organisms on the planet as they play a vital role in the biosphere and have great economic importance on account of both their benefits and harmful effects.
Following are some of the important uses of fungi:
- Recycling – They play a major role in recycling the dead and decayed matter.
- Food – The mushrooms species which are cultured are edible and are used as food by humans.
- Medicines – There are many fungi that are used to produce antibiotics and to control diseases in humans and animals. Penicillin antibiotic is derived from a common fungus called Penicillium.
- Biocontrol Agents – Fungi are involved in exploiting insects, other small worms and help in controlling pests. Spores of fungi are used as a spray on crops.
- Food spoilage – Fungi play a major role in recycling organic material and are also responsible for major spoilage and economic losses of stored food.