Saturday, June 30, 2018

Kingdom Fungi


  • Father of mycology- Pier' Antonio Michelli.
  • Father of Systematic mycology - E. M. Fries .
  • Father of modern mycology and plant pathology- H. A. de Bary.
  • Father of indian mycology and plant pathology - E. J. Butler.
  • K. R. Kirtiker was first indian scientist who collected and identified Fungi.

Distribution

 There are more than 100,000 species of fungi, which are cosmopolitan in distribution.


Habitat:

 Fungi are ubiquitous i.e. found almost everywhere. They flourish well in moist, dark and warm habitat. The most usual habitat of Fungi is wet soil rich in humus. A few forms are aquatic (e.g., Saprolegonia, Allomyces, Achyla ).
Nutrition

  • Fungi lack chlorophyll and are unable to synthesize their own food by photosynthesis. Therefore, they obtain their nutrition from the external source by absorption and by the process of extra cellular digestion. Such mode of nutrition is called Saprophytic mode of nutrition.
  • Some fungi are symbiotically associated with algae to form Lichens. A few forms symbiotic association with the roots of higher plants (e.g., Pinus) known as mycorrhiza.

Thallus Organization

  • The plant body of fungi is thallus which may be acellular or multicellular. Acellular thallus may be motile (e.g., Synchytrium ) or non-motile (e.g., Saccharomyces).  Multicellular thallus is tubular, filamentous, branched and is called mycelium. The unit is of mycelium is hyphae.
  • The mycelium may be aseptate and septate. Aseptate mycelium lacks septa. It is multinucleate and is called Coenocytic, e.g., Phycomycetes. In aseptate mycelium, septa formation occurs at the time of injury and during separation of reproductive structures. Septate mycelium is partitioned into separate compartments by means of cross walls(septa). Individual cells may be uninucleate, Binucleate and multinucleate.
  • Each septum is perforated by a central pore. The pore may be simple or dolipore[barrel-shaped swelling around their central pore].
  • Mycelium may be eucarpic[only a part forms reproductive body] or holocarpic[the whole mycelium is transformed into reproductive body].

Cell Structure

  • Fungi are eukaryotic and posses true nuclei. Fungal cells are bounded by definite cell wall. The cell wall is made up of Chitin/ Fungal cellulose[nitrogen containing polysaccharide or heteropolymer of acetyl glucosamine which is also found in insects]. True cellulose is found in cell wall of some Phycomycetes (e.g., Phytophthora).
  • The cell wall encloses protoplast, which is differentiated into plasma membrane, cytoplasm, nucleus and vacuoles. Cytoplasm has all the eukaryotic cell organelles, except plastids. The dictyosomes are also not typical. Lomasome is a convoluted complex of membranous outgrowth of plasmalemma.
  • Vacuoles are many but small.
  • Nuclei are smaller as compared to those of higher plants. Nuclei undergo intranuclear spindle formation[karyokinesis, Moore, 1961].
  • Food reserve is glycogen[animal starch] and oils.

Reproduction

  • Reproduction can be vegetative, asexual and sexual.

Vegetative Reproduction

Vegetative reproduction occurs by the following methods:-
  1. Fragmentation :- Mycelium may break accidentally or due to decay into two or more parts. each segment develops into complete mycelium.
  2. Fission :- It occurs into unicellular forms where cell division produces two daughter cells. e.g., Yeasts. 
  3. Budding :- The protrusion grows out into a bud. The bud constricts at the base and separates into new individuals e.g., yeast. Sometime a number of buds may be seed attached to the parent cell[Torula stage].
  4. Chlamydospores :-  They are thick walled, black, multinucleate resting spores formed by the collection of protoplasm at one or many places. They are mostly intercalary and after the separation, germinate to produce new mycelia.e.g., Rhizopus, Mucor, Ustilago etc.
  5. Oidia/Arthrospores:- Oidia are thin walled structures produced in chain. They are formed by the segmentation of hypha in presence of excess water, sugar and salts. They germinate immediately after liberation and produce new mycelia, e.g., Mucor. The Oidia formation in Mucor represents Torula stage.

Asexual reproduction

  • Asexual reproduction is accomplished by means of asexual spores formed by mitosis, so also called mitospores. Asexual spores are of two types, motile[zoospores] and non-motile[aplanospores].

Zoospores

  • The zoospores are thin walled flagellate spores produced inside a sac like structure known as zoosporangium. Zoospores may be uniflagellate or biflagellate. The flagella occur anteriorly, laterally or posteriorly, e.g., aquatic fungi.

Aplanospores

  • Aplanospores are of two types, sporangiospores and conidia.
  • Sporangiospores are thin walled, non-motile, uni or multinucleate spores produced endogenously in sporangium. After dispersal and germination they produce new mycelia, e.g., Rhizopus, Mucor etc.
  • Conidia(Gr. konis- dust, idion - diminutive) are non-motile, thick walled asexual spores produced exogenously at the tip of special hyphae, called conidiophores in a basipetal succession. Conidia are dispersed by wind. On falling on suitable substratum, each conidium produces a new mycelium e.g., Penicillium, Aspergillus etc.

Sexual Reproduction

  • Most true fungi reproduce by sexual method, but in the members of the fungi imperfecti (Deuteromycetes), the sexual stage is either absent or unknown. The sexual reproduction in true fungi is affected by the fusion of two nuclei of different parentage, which may be carried in motile or non-motile gametes, in gametangia, or insomatic cells of the thallus.

Types of sexual reproduction

  • There are different types of sexual reproduction in different groups of fungi.

Sex organs 

  • There are two types of organs(gametangia) male and female. The male sex organ is called anthredium while the female sex organ is called oogonium(in the members of Oomycetes) or ascogonium( in the members of Ascomycetes).There is no development of sex organs in the members of Basidiomycetes, though they reproduce sexually  by somatogamy. There is no sexual reproduction at all in the members of Deuteromycetes, so they are called fungi imperfecti.

Classification of Fungi

  • A number of criteria are used for classification of fungi. The important ones are morphology of vegetative structures, morphology of reproductive structures, types of meiospores and mitospores, life cycle, physiology, biochemistry etc.