Observations on the Trapping of Nematodes by Dactylaria Scaphoides Using Optical, Transmission and Scanning-Electron-Microscopic Techniques

Utilization of Nematode Destroying Fungi for Management of Plant-Parasitic Nematodes-A Review

Nematode destroying fungi are potential biocontrol agent for management of plant-parasitic nematodes. They inhibit nematode population through trapping devices or by means of enzymes and metabolic products. They regulate nematode behavior by interfering plant-nematode recognition, and promote plant growth. For more effective biocontrol, thorough understanding of the biology of nematode destroying fungi, targeted nematode pest and the soil ecology and environmental condition in the field is necessary. This review highlights different types of nematode destroying fungi, their mode of action as well as commercial products based on reports published in this area of research.

Low-temperature scanning electron microscopy in fungus-nematode interaction

A comparative study has been made of different preparation techniques used for the scanning electron microscope (SEM), with regard to their application to fungus-nematode interaction. The preparation of frozen-hydrated specimens of both healthy and Arthrobotrys-oligospora-infected second-stage larvae of the root-knot nematode (Meloidogyne sp.) is described, and the results are compared with those obtained by critical point-drying and freeze-drying. In all cases the frozen-hydrated specimens consistently showed the best preservation.

An improved method for light- and electron microscopial studies of nematode/fungal interactions

A method is presented that enables studies to be made of single nematode-fungal interactions under conditions where fungal growth at the expense of external nutrients is prevented. The nematophagous fungus Arthrobotrys oligospora was used as a model organism in these studies. The method is based on removal of the traps from the vegetative mycelium, immediately after a nematode was captured and transfer of the trap with the captured nematode into a droplet of sterile distilled water placed in a moisture chamber. In the absence of external nutrients, such isolated traps of A. oligospora were fully effective in penetrating and subsequently digesting the captured nematode. Solely vegetative mycelium was formed at the expense of the digested nematode; this developed from the trap that originally had captured the nematode. One advantage of the present method is that studies on various stages of the nematode-fungal interaction can now be performed under conditions that exclude major influences of external nutrients which otherwise could be communicated to the trap cells by way of the vegetative mycelium.

[Zoophagous fungi]

Fungi which kill microscopic animals of different systematic origin by capturing, invading, and digesting them are described. The focal point is nematode destroying fungi, as being the most abundant, most often isolated and most intensively studied. Their ecology and their probable role in the control of nematodes are discussed.

An electron-microscopical analysis of capture and initial stages of penetration of nematodes by Arthrobotrys oligospora

A detailed analysis was made of the capture and subsequent penetration of nematodes by the nematophagous fungus Arthrobotrys oligospora using different electron-microscopical techniques. Capture of nematodes by this fungus occurred on complex hyphal structures (traps) and was effectuated by an adhesive coating, present on these trap cells. The adhesive layer was largely fibrillar in nature and was absent on cells of normal hyphae. Following capture, penetration hyphae were formed at those sites where the trap cell wall was anchored to the nematode cuticle by the adhesive. New walls of these hyphae were formed underneath the original trap cell walls, which were partly hydrolysed to allow growth and development of the penetration tubes through the adhesive coating towards the cuticle. Our observations indicated that the cuticle of the nematode was subsequently penetrated by the penetration tubes by mechanical means. After penetration a large infection bulb was formed from which trophic hyphae arose. Cytochemical experiments indicated that the sites of penetration of the cuticle were intensely stained for acid phosphatase activity. At later stages of infection activity of this enzyme was present throughout the nematode contents; the enzyme was most probably secreted by complex membranous structures associated with the cytoplasmic membrane of the infection bulb and the trophic hyphae.

Binding Characteristics of Lectins Involved in the Trapping of Nematodes by Fungi

Seventeen saccharides were tested for their ability to bind to the trap lectins of three species of nematode-trapping fungi and prevent nematode capture. The lectin of Arthrobotrys conoides was found to be inhibited by α- d -glucose/ d -mannose and similar saccharides. The lectins of Monacrosporium eudermatum and Monacrosporium rutgeriensis were inhibited by α- l -fucose and 2-deoxy- d -glucose, respectively. Human group O(H) erythrocytes agglutinated to traps of M. eudermatum but not A. conoides or M. rutgeriensis. There was no agglutination of group A or B to traps formed by all three fungi. Exposure of the traps to trypsin eliminated the ability to capture nematodes. The presence of d -glucose/ d -mannose and l -fucose residues on the nematode cuticle was suggested through the use of commercially prepared lectin-peroxidase conjugates.