The Predaceous fungi are also termed as Nematophagous fungi. The Nematophagous fungi are of three main types on the basis of ecological habitat:
a. Nematode trapping fungi,
b. Endoparasitic fungi,
c. Egg parasites.
Nematode trapping fungi: Fungi capturing Nematodes are called Nematode trapping fungi. Such fungi are evolved structural adaptations to trap or penetrate their prey. They may be Predatory or Endoparasites. There are a varieties of ways by which fungi trap Nemetodes resulting in their death.
Adhesive Hyphae: The fungal Hyphae form adhesive which capture Nematodes. These Hyphae produce adhesive any point in response to Nematode contact or the Hyphae are coated with adhesive along their entire surface. At the point of Hyphae where contact is made for capture, a thick and yellowish chemical material is secreted. An outgrowth of Hyphae similar to Appressorium develops. When the Nematode is trapped it becomes inactive first and killed in the last after penetration of hyphae.
Adhesive branches: The Nematode trapping fungi produce the most primitive and simple organ of capture, the adhesive branches, which are a few cells in height. From the main prostrate Hyphae short laterals grows as erect branches on or below the substrate.
Adhesive nets: Nets are formed by fungal Hyphae (coated with adhesive material) which are adhesive in nature. Nets may be in the form of a single hoop like loop to a complex multi-branched networks.
Adhesive knobs: A distinct adhesive cell is produced at the apex of a slender non-adhesive stalk containing 1-3 cells. A thin film of adhesive material is produced over the surface of knob.
Non-Constricting rings: From the prostrate creeping septate hyphae there arise erect and lateral branches which form non-constricting rings. Initially the branch is slender but widens subsequently and being curver to form a circular structure. At the point where tip of branch makes contact with supporting stalk, cell walls get fused. This results in formation of three-celled ring with a stalk.
Constricting rings: The constricting rings are produced similar to non- constricting rings but the supporting stalk is shorter and stouter.
The body of Nematode consists of a low molecular weight peptide which is called Nemin. Nemin is water soluble and potential stimulant for trap formation. It causes morphological changes in Nematophagous fungi. The lectin of fungus A. oligospora binds especially to the sugar, N-acetyl-D-galactosamine, present on Nematode cuticle. The trapped Nematodes secrete mucilage which has been identified under electron microscope. The Nematode cuticle is lysed at the point where lectin combines with N-acetyl-D-glucosamine.The enzyme collagenase is secreted by the fungus which dissolves collagen protein of Nematode cuticle.
Endoparasitic Fungi: The Endoparasitic fungi do not extensively produce mycelium external to Nematode body. The Endoparasitic fungi are species of Cephalosporum, Meria, Verticillium, Catenaria, Meristacrum etc.
Catenaria anguillulae produces zoospores which track down Nematodes by swarming, eventually encyst near Nematode body orifice, penetrate and colonize the prey. The encysted zoospores produce germ tube which penetrate Nematode through orifice or by dissolving cuticle. The infectious hyphae grow well inside Nematode body, digest content and lyse the prey.
In Meristacrum asterospermum forms adhesive conidia which attach to the cuticle of Nematode. It germinate to form the hypha which swells and acts as infectious thallus. Adhesive spores are also produced by species of Meria, Cephalosporium and Verticillium. In M. coniospora an adhesive bud develops at the distal end of tear drop shaped spores.
Egg parasites: There are a few saprophytic fungi which attack on nemtode eggs. When a fungal hypha comes in contact of an egg, a swollen structure at terminal portion develops at the point of contact. It gets attached to the egg, a swollen structure at terminal portion develops at the point of contact. It gets attached to the egg where from a marrow infectious tube develops that penetrates the shell of the egg.The hyphae swell up to form appressorium from which numerous irregularly branched absorption hyphae develops that consumes egg nutrients. Ex. Dactyllele oviparasitica, Paecilomyces lilacinus etc.
About Author / Additional Info: