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a wilting of plants caused by various agents. Most often wilt is called tracheomycotic disease, caused by imperfect fungi Verticillium dahliae (verticilliosis) and Fusarium oxysporum (fusarium wilt). The former affects approximately 350 species of dicotyledonous plants. The plant that is most susceptible to wilt is cotton; less susceptible plants include sesame, Indian mallow, flax, tomatoes, potatoes, musk-melons, watermelons, peaches, and apricots.
The causative agent develops in the soil, penetrates the plant through the root, and spreads in the water transport system of the xylem, causing wilting of subterranean organs. Most often the whole plant dies; more rarely, certain of its parts. The disease is transmitted through soil, by plant remnants, planting material, and irrigation water. (Fusarium wilt is also transmitted by seeds.) Affected plants either yield no harvest or their quality is sharply decreased. Control measures are selection of wilt-resistant varieties, purging the soil of wilt agents by introducing rational crop rotation and soil cultivation, and introduction of organic fertilizers that activate development of saprophytic microbes and fungi-antagonists of wilt agents.
REFERENCESSolov’eva, A. I. “Spetsializatsiia formy Verticillium dahliae Kleb.” In the collection Bolezni khlopchatnika. Tashkent, 1938.
Raillo, A. I. Griby roda fuzarium. Moscow, 1950.
Materialy Vsesoiuznogo simpoziuma po bor’be s viltom khlopchatnika. Tashkent, 1964.
A. I. SOLOV’EVA
a plant disease characterized by the drooping of leaves, branches, and other organs owing to loss of turgor (tension of tissues) and often by the formation of spots on the leaves. Wilt is observed when entire plants or parts of plants are attacked by parasitic microorganisms (bacteria, fungi, and—less commonly— viruses and Mycoplasma). The condition may also result from mechanical injury to the root system, intensive evaporation of water from the leaves, insufficient water in the soil, or other unfavorable factors. Both herbaceous and woody plants are subject to wilt.
In cases of infectious disease, wilt is distinguished as a type of plant disease and as a symptom. In the latter instance, wilt accompanies certain infectious diseases most often associated with the root system (for example, clubroot of crucifers and big bud of potato) and is observed mainly in the final stage of the disorders. Wilt produced by bacteria is known as tracheobacteriosis, and wilt caused by pathogenic fungi is called tracheomycosis. The causative agents live in soil or on plant remains and penetrate the vascular system of the plant through the roots. Severe decrease in cell turgor is caused by the toxic substances secreted by microorganisms.
Control measures include proper crop rotation, implementation of measures that promote the accumulation of water or prevent the unproductive expenditure of water (for example, evaporation) when there is a water deficiency in the soil, and decontamination of seeds. Other important measures are the gathering and burning of plant remains and roots, deep autumn plowing, destruction of weeds, and removal of severely diseased plants from the fields. Also important are proper plant care, the application of fertilizer, and the use of wilt-resistant varieties.
L. M. LEVKINA