Nutrition of Fungi
Modes of nutrition.
All fungi are characterised by the complete absence of photosynthetic pigment-the chlorophyll. Hence they lack the ability to manufacture their own organic food. They are, therefore, dependent upon living. They are organisms or dead organic matter for their nutrition. On the basis of food habits fungi can be grouped into following three classes.
(a) Parasites or parasitism
Those fungi which obtain their food from other living organisms (plants or animals) are called parasites. The organism on which a parasite lives is known as the host. Many parasites grow only on the host surface and send out specialized absorbing organs called haustoria within the host tissue for food absorption. Such parasites are called ectoparasites or ectophytic parasites (e.g. Erysiphe, Mucor). Some of the other parasitic fungi which grow inside the host tiss (intracellular) are called endoparasites of endophytic parasites (e.g., Pythium, Puccinia).
Among fungi, different levels of parasitism may exist. These are briefly discussed below.
(i) Obligate (total or complete)
parasites. These fungi obtain their food from the host throughout their life without which they can not complete the life cycle; e.g., Albugo, Puccinia.
(ii) Facultative (partial by chance)
saprophytes. These fungi are normally parasites but under certain circumstances may obtain their food from dead organic matter, i.e., may lead saprophytic life; e.g., Ustilago.
(b) Saprophytes.
Fungi which obtain their food from dead and decaying organic matter, are called saprophytes. Saprobes may be further divided into following two categories.
(i)Obligate saprophytes.
These fungi always obtain their food from dead matter throughout their life and do not require living organisms; e.g Mucor, Saprolegnia.
(ii) Facultative parasites.
These fungi are normally saprophytic but under certain conditions become parasites and obtain their food from a living host; e.g., Pestalotia.
(c)Symbionts.
It is an organic relationship between two individuals in which both the partners are benefited. Two common examples of symbiosis are (i) lichens and (ii) mycorrhiza. Lichen is a composite plant formed by the association of algae and fungi. The algal partner belongs to Chlorophyceae or Cyanophyceae and the fungal partner is a member of Ascomycetes or Basidiomycetes. Mycorrhiza is an association between fungal hyphae and roots of higher plants as in Pinus.