Nematode Plant Disease
Nematode Plant Disease
a plant disease caused by harmful herbivorous nematodes. Nematode plant diseases are observed in many cultivated and wild herbs, trees, and shrubs.
The general symptoms of nematode plant diseases include delayed appearance and retarded growth of shoots, poor blossoming, and partial (sometimes considerable) death of plants at a young age. Agricultural plants experience a decrease in harvest; sometimes there is no harvest. The infestation of nematodes in plant roots may lead to intense branching of the root system and the decay of small roots (golden nematode, Heterodera avenae) or to the formation of variously shaped galls (gall nematodes on the roots of vegetable and industrial crops), acute swellings known as rostella (the eelworm Anguina radicicola on the roots of wild grasses), and ulcers that lead to root atrophy (nematodes of the genus Paratylenchus). By disrupting the root system during feeding, the nematodes facilitate penetration of the plant by pathogenic fungi, bacteria, and viruses.
Stem nematodes cause spindle-shaped thickening of the stems, underdevelopment and deformation of the leaf blade (in phloxes), swelling of the leaf petioles and stolons, corrugation of the leaf blade (in the strawberry), formation of soft, dark spots on the periphery of tubers (in potatoes), loosening of the tissue of succulent scales, and dehiscence of the bulb stem (in bulbous plants). The strawberry nematode (Aphelenchoides fragariae) causes abnormal crown formation and underdevelopment of the leaf blades around the central vein.
Leaf nematodes infest chrysanthemums, begonias, rudbeckias, gloxinias, and ferns. The first symptom of leaf infestation is the atrophy of those parts of the leaves between the veins; the entire blade subsequently turns brown and dries. When nematodes parasitize the floral parts of wheat, spelt, and rye, fertilization does not occur; the female organs are converted into galls that resemble grain but are brown in color and that have a hard casing and a mass of nematode larvae inside (Anguina tritici). The spike is shortened and has wavy awns; the plants mature late. White tip, a disease of rice caused by the nematode Aphelenchoides besseyi, is characterized by whitening (decolorization) of the leaf apices, emaciation of the plant, undeveloped seeds, or the absence of grain. Nematodes in various stages of development are found under the spike scales. Ufra disease, another disease of rice, is caused by the nematode Ditylenchus angustus and leads to plant starvation and empty grains.
The causative agents of nematode plant diseases, upon entering the soil, are carried to other areas in water and by agricultural implements and the wheels of vehicles and by rooted seedlings.
Control measures include treating infected plants and soil with nematocides, sanitizing planting and seed materials, introducing higher standards of fecal fertilizers, using trace elements against gall nematodes, rotating crops with those that are not infected, and introducing resistant varieties of vegetables, potatoes, and cereals.
REFERENCESKir’ianova, E. S., and E. L. Krall’. Paraziticheskie nematody rastenii i mery bor’by s nimi, vol. 2. Leningrad, 1971.
Decker, H. Nematody rastenii i bor’ba s nimi. Moscow, 1972. (Translated from German.)
N. M. SVESHNIKOVA