Fungi: General Characters
The word fungus (plural ; Fungi) is a Latin word meaning mushroom. The branch of science that deals with study of fungi is called mycology and branch that deals with the study of fungal diseases is called fungal pathology.
Fungi are group of those plants whose form is thallus and are mostly haploid, build of single cell (unicellular) or cells (multicellular) that posses definite cell wall and nucleus but lack chlorophyll (achlorophyllous) and heterotrophic.
They are cosmopolitan in distribution and are ubiquitous i.e. occur in any habitat where life is possible. Fungi are a very large group having about 5,100 genera and more than 50,000 species.
Most of them are moisture loving and terrestrial and a few are aquatic (e.g saprolegnia). Many species are parasitic, infecting plants, animals and human-beings and few are epiphytic (e.g. Armillaria on apple tree cause red rot of apple). Grow well at 20-30 degree celsius and at acidic pH 6.0.
They are heterotrophic and according to mode of nutrition they may be
1. Parasites. Those fungi which obtain their nutrition from other living plants or animals are known as parasites and they are further may be
a. Obligate parasites: e.g. Albugo, Ravenelia, Puccinia. It may be further Biotrophs, Hemibiotrophs or Perthotrophs.
b. Facultative saprophytes: e.g. Ustilago, Sphacelotheca, Tolyposporium
2. Saprophytes. It include those fungi which obtain their nutrition from the dead decaying organic matter and they are further may be
a. Obligate saprophytes:. E.g. Mucor mucedo, Agaricus, Morchella
b. Facultative parasites: E.g. Furarium, Pythium
3. Symbionts. Some fungi grow on other living organisms and both are mutually benefited and such association is known as symbiosis. E.g Lichens and mycorhiza.
The reserve food material is in the form of glycogen and oil globules.
The thallus consists of long, tubular, branched filaments called hyphae (gk word web) and which together form a net like structure called mycelium. The hyphae are
· Aseptate and coenocytic (Phycomycetes)
a. Uninucleate (monokaryotic)
b. Binucleate (dikaryotic)
The septa are of 3 types: complete septum, septum with simple pore and septum with dolipore (Basidiomycetes). In dolipore the edges of septa around pore are swollen and forms septal pore cap or parenthosome. These septal pores form a valve like structure. Septal pores allow quick transport of nutrients from the region of absorption to all parts of the mycelium.
Modification of mycelium
In majority of fungi the hyphae form a net like structure, but in some advanced fungi they may undergo certain modifications is response to functional needs such as
(a) Prosenchyma: When the hyphae lie more or less parallel to one another and unite to form a rather loosely interwoven structure so that their individuality is not lost.
(b) Pseudo-parenchyma: In this the hyphae become closely intertwined and lose their individuality and are not distinguishable from each other. They form a compact mass of parenchymatous like tissue of higher plants in cross section.
(c) Rhizomorph. The hyphae are interwoven and form a root like structure, lose their individuality and the whole mass behaves as an organised unit. It has a higher infection capacity than individual hyphae
(d) Sclerotium (Sclerotia): In this the aggregation and adhesion of hyphae form a compact globose structure. It may survive for long period and represents the resting stage of the fungus. It contain reserve food and thus help in vegetative propagation
(e) Stroma: It is thick mycelia mat in which a large number of fruiting bodies develop.
It is a motile body and is the characteristics feature of some lower fungi and is absent in higher fungi. The flagella are of two types:
(1) Whiplash (acronematic) flagella are smooth with 9+2 organisation,
(2)Tinsel (pantonematic) flagella with numerous minute hair-like mastigonemes on their surface.
They reproduce by asexual and sexual methods. The vegetative reproduction is generally considered under the category of asexual methods. Fungi may show Holocarpic or Eucarpic condition.