Virus Transmission by Nematodes

Abstract

All known virus-transmitting nematodes (eelworms) are ectoparasites.They belong to two families in the order Dorylaimida, Longidoridae and Trichodoridae, with the following characteristics:Family: Longidoridae (genera: Longidorus,Xiphinema). Slender, 4–8 mm long nematodes with 80–140 µm long hollow odontostyle. For feeding, the stylet is inserted in the deeper layers (vascular cylinder) of root tips of a host plant and, after production of saliva, the cell contents are sucked up by the stylet. The punctured cells develop some necrosis, whereas the root shows swelling of the tip and reduced cell elongation. Several species of both genera transmit the icosahedral nepoviruses. In spite of the fact that virus does not circulate or multiply in the body of the nematode, there is a considerable degree of virus-vector specificity.Family: Trichodoridae (genera: Trichodorus,Paratrichodorus). Rather plump, 0.5–1.5 mm long nematodes with a 20–80 µm long stylet (onchiostyle; a slender tooth implanted on the dorsal pharyngial wall). Similar to the Longidoridae, they feed on root tips but also on growing tips of stem parts in the soil. The stylet, being a rather short tooth, is used only to tear the wall of epidermal cells by repeated thrusts while the lips are pressed firmly against it to suck in the cell contents. The nematodes also feed on cells of the deeper layers as soon as they become exposed after destruction of the epidermal cells. The root reacts by stopping cell elongation and starts division of cells below the attacked ones. Trichodoridae transmit only the rod-shaped tobraviruses, i.e. tobacco rattle virus and pea early browning virus.