(also phytohelminth, phytonematode), a parasitic worm of plants, belonging to either of the orders Tylenchida and Dorylaimida, of the class of roundworms (Nematoda). The body ranges from 0.2 to 3–5 mm in length and from 10–15 to 100 microns in width. Some members of the genus Longidorus attain a length of 10–11 mm.
Plant helminths are divided into two groups; one parasitizes the aboveground parts of the plant, while the other parasitizes the root system or various plant organs. Some species cause the formation of galls that are peculiar to that parasite. Infected plants are usually retarded in growth and development. Deformities of certain organs are observed, for example, proliferations, curvatures, and dwarfism.
The USSR has about 400 species of plant helminths, but only a few dozen of them are considered serious pests. The most harmful are the potato and sugarbeet nematodes of the genera Globodera and Heterodera and the stem nematodes that infest potatoes and onions. Severe damage is done by gall nematodes of the genus Meloidogyne, especially in hotbeds and open ground in southern regions. The branch of science that studies plant helminths is plant helminthology.
E. S. KIR’IANOVA