CLASSES OF FUNGI -
Phycomycetes :
- Found in aquatic habitat, on decaying wood in moist and damp places.
- Some of them are obligate parasite on plants.
- Mycelium is aseptate and coenocytic
- Asexual reproduction by zoospores (motile) or by aplanospores (nonmotile).
- Spores are produced endogenously in sporangium.
- Zygospore produced by fusion of gametes.
e.g., Rhizopus, Albugo.
Ascomycetes :
- Commonly known as ‘sac fungi’.
- Unicellular (yeasts) or multicellular (e.g. Penicillium)
- Saprophytic, decomposers, parasitic or coprophilous.
- Mycelium branched and septate.
- Asexual spores are called conidia produced exogenously on the conidiophores. Conidia on germination produce mycelium.
- Sexual spores are called ascospores produced endogenously in ascus produced inside fruiting body called Ascocarp.
e.g., Aspergillus, Neurospora.
(iii) Basidiomycetes
- Common known forms called mushrooms, bracket fungi or puffballs.
- Mycelium septate and branched.
- Asexual spores generally are not found.
- Vegetative reproduction by fragmentation.
- Sexual reproduction by fusion of vegetative or somatic cells of different strains to form basidium produced in basidiocarp.
- Basidium produces four basidiospores after meiosis.
e.g., Agaricus, Ustilago.
Deuteromycetes :
- Called as ‘Fungi Imperfecti’ as sexual form (perfect stage) is not known for them.
- Once sexual form is discovered the member is moved to Ascomycetes or Basidiomycetes.
- Mycelium is septate and branched.
- Are saprophytic, parasitic or decomposers.
e.g., Alternaria, Colletotrichum.
Viruses :
- They did not find a place in classification. Take over the machinery of host cell on entering it but as such they have inert crystalline structure. So, difficult to call them living or non-living.
- Pasteur gave the term ‘Virus’ i.e., poisonous fluid.
- D. J. Ivanowsky (1892) found out that certain microbes caused Tobacco Mosaic Disease in tobacco plant.
- M. W. Beijerinek (1898) called fluid as ‘Contagium vivum fluidum’ as extracts of infected plants of tobacco could cause infection in healthy plants.
- W. M. Stanely (1935) showed viruses could be crystallised to form crystals of protein which are inert outside their specific host.
Structure of Virus :
- Its a nucleoprotein made up of protein called Capsid. Capsid is made up of capsomeres arranged in helical or polygeometric forms. Have either DNA or RNA as genetic material which may be single or double stranded.
- Usually plant viruses have single stranded RNA; bacteriophages have double stranded DNA and animal viruses have single or double stranded RNA or double stranded DNA.
Diseases caused : Mumps, Small pox, AIDS etc.
Viroids :
- Infectious agent, free RNA (lack protein coat)
- RNA has low molecular weight.
- Causes potato spindle tuber disease.
- Discovered by T. O. Diener in 1971
Lichens :
- Symbiotic association between algal component (Phycobiont) and fungal component (Mycobiont). Algae provide food. Fungi provide shelter and absorb nutrients for alga.
- Good pollution indicators as they do not grow in polluted areas.
