Nutrition in Fungi

 Nutrition in Fungi

As fungi are achlorophyllous , they cannot produce their own food . Thus all fungi exhibit heterotrophic mode of nutrition. Usually fungi prefer to grow in shade and moist habitats. Some prefer to grow in darkness or dim light. Generally, fungal growth is prevalent where there is availability of living or dead organic matter along with congenial temperature. On the basis of their mode of nutrition, the fungi are divided into the following three categories : 

a . Parasites

Fungi which obtain their nutrients from living organisms are called parasites. If it grows on the external surface of the host, it is called ectoparasite. When it enters inside the host and feeds within, such parasitic fungi are called endoparasites. The living organism infected by a parasite is called a host and the abnormal conditions of the host due to the infection by the parasite is called disease. Parasites are of two types :

1. Obligate parasites: Fungi which are entirely dependent upon living host tissue are called obligate parasites . They are non culturable on the artificial or synthetic medium as their dependence on living host is obligatory . Obligate parasites are commonly found in the order Perenosporales , Erysiphales and Uridinales ( e.g. Erysiphe , Perenospora , Albugo etc.) .

2. Facultative parasites: Normally these fungi are saprophytic but in certain circumstances they are capable of exhibiting parasitic mode of nutrition. The species under the genus Armillaria are good examples of facultative parasite parasites. They usually grow as parasite in the living trees, but if the tree dies they adopt saprophytic mode.

b.  Saprophytes

Fungi obtaining their food material from dead organic matter are known as saprophytes. Saprophytic fungi produce extracellular enzymes into the substratum by which complex organic materials are converted into simple and consumable forms . Saprophytes are of two types such as 

1 . Obligate Saprophytes : When fungi grow only on organic matter and do not have the capacity to infect the living plants or animals , such fungi are called obligate saprophyte . Examples : Mucor, Aspergillus.

2.  Facultative saprophytes: The fungi which are mainly parasitic organisms but have their ability to survive for a part of their life cycle as a saprophyte is called facultative saprophytes . Examples : include Phytophthora and Botrytis . Modern mycologists use the term biotroph for parasites and necrotroph for saprophytes. 

c. Symbiotic fungi : 

Some fungi live in close . association with higher plants where they are mutually benefitted. Such mutual association is called symbiosis and the participants are called symbionts . Two striking examples of symbiotic association are lichen and mycorrhiza .

Lichen Fungus forms symbiotic association with lichen thallus and both are beneficial to each other. The two organisms in this association are intertwined and form a single composite thallus organization which is totally different in form and habitat from either of the partners. The fungal partner is responsible for the absorption of inorganic nutrients and water whereas the algal partner synthesizes the organic food.

Mycorrhiza ( Plural- Mycorrhizae or Mycorhizas): It is defined as the symbiotic association between the hypha of certain fungi and roots of plants. Here the fungi absorb their food from the roots of the plant and in return provide lots of benefits to the plant.