Fungi : Mode of Nutrition in Fungi

In this article we will discuss the Mode of Nutrition in Fungi (1) Saprophytes (2) Parasites (3). Symbionts (4). Predacious fungi

• Fungi are heterotrophic in nutrition
• They are chlorophyll deficient plants and hence they cannot manufacture carbohydrates using carbon dioxide, water and sunlight
• Fungi are with simple structural organization, thus they always depends on dead or living organic matter for their energy requirements

• On the basis of mode of nutrition, fungi are classified into four groups:

1. Saprophytes
2. Parasites
3. Symbionts
4. Predacious fungi

(1). Saprophytes

• Saprophytic fungi obtain nutrition from dead organic matter
• These fungi lives on dead organic matter or excreta of both plant and animal origin
• Examples: Mucor, Rhizopus, Penicillium and Aspergillus
• Vegetative hyphae of these fungi directly absorb food materials from organic matter
• Saprophytic fungi may be of two types:-

1. Ectophytic saprophytes: grown on the surface of organic matter
2. Endophytic saprophytes: grown inside the organic matter

• In some ectophytic fungi such as Rhizopus, special absorptive structures such as rhizoids are developed for the easy absorption of food materials
• Saprophytic fungi produce exo-enzymes (enzymes which acts outside the cell)
• These enzymes digest the complex organic matter in the substratum into simpler compounds to facilitate easy absorption by the hyphae

(2). Parasites

• Parasitic fungi take food from other living plants or animals
• The living organism on which the fungi parasitize are called host
• Parasitic fungi are harmful to the host and they produce disease condition in host organisms
• The relationship of host and parasite in pathology is known as parasitism
• Parasitic fungi are of three types:-

1. Obligate parasites: these fungi can live only as parasite on a living host Obligate parasites cannot live on dead organic matter Example: Puccinia which cause rust disease in several crop plants including wheat
2. Facultative saprophytes: They are parasites, but they can also survive on dead organic matter in the absence of living host Example: Taphrina
3. Facultative parasites: these fungi usually follow saprophytic mode of nutrition Under certain conditions, they parasitize suitable host plants Example: Fusarium and Pythium which cause soft rot disease in crop plants

• On the basis of location of parasite in host organism, the parasites may be:

1. Endoparasite: parasite live inside the host tissue
2. Ectoparasite: parasite fungi which live on the outside surface of host

• Parasitic fungi possess specialized absorptive structures called haustoria for the absorption of nutrients from the host cells
• Haustoria are specialized hyphal modifications
• Haustoria may be inter-cellular (occupy between two cells) in intra-cellular (occupy
• within the cell)
• Size and shape of haustoria varies in different fungal groups
• Haustoria may be round, knob like, club like or branched

(3). Symbionts

• These fungi grow on or with other living organism but both of them are mutually benefited
• Lichens and mycorrhiza are examples
• Lichens are the symbiotic association between algae and fungi
• Here both fungi and algae are mutually benefited
• Algae synthesize carbohydrates where as the fungi provides shelter for algae
• Mycorrhizae are the symbiotic association between fungi and roots of some higher plants
• Mycorrhizae helps in the absorption of nutrients by the host plant
• Mycorrhiza may be ectophytic or endophytic
• Ectophytic mycorrhiza are external mycorrhiza and they are confined to the outer region of the roots
• Endophytic mycorrhiza are internal mycorrhiza and they are found deeply in the root cells

(4). Predacious fungi

• They are animal capturing fungi (predators)
• These types of fungi possess special hyphal traps called snares to tap and capture small animals such as nematodes and protozoa
• They usually inhabit in the soil
• They possess rapidly constricting hyphal traps which hold the captive for long time
• They also have haustoria which directly inserted into the tissue of the prey
• Some predacious fungi also produce sticky secretions for capturing nematodes
• Examples of predator fungi: Arthrobotrys, Dactylella, Dactylaria