Xanthomonas campestris pv. translucens (Jones, Jonson and Reddy) Dye - Black Chaff of Wheat.
Systematic position.Kingdom Procaryotae, section Gram-negative aerobic rods and cocci, family Pseudomonadaceae, genus Xanthomonas.
Synonyms.Bacterium translucens (Jones, Jonson and Reddy) Stapp, Phytomonas translucens (Jones, Jonson, Reddy) Bergey, Harrison, Breed, Hammer and Hunton, Xathomonas translucens (Jones, Jonson, Reddy) Dowson.
Morphology and biology.Bacteriosis attacks leaves, stems, and ears. At the first stage of disease development, small oblong aqueous, translucent spots of light green color appear on leaves. Then these spots expand and turn yellow to brown, even black. Sticky slime (exudate) is observed on spots, forming a yellowish film at drying. Leaves may die off at strong affection. Black or brown stripes are formed on stems. Stem below ear is sometimes completely brown. Blacking occurs on distal part of ear scales, later brown lateral stripes appear along the scales. Strongly diseased plants form no ears. Affected plants give only puny grain having yellow stripes. Cells of X. campestris pv. translucens are straight rods, usually 0.5-0.8 x 1.0-2.5 mkm, moving by means of polar flagella. Aerob. Gram-negative. Non-sporing. Forming capsules. Colonies are round, smooth, yellow, shining, with even borders. Diluting gelatin slowly. Not reducing nitrates. Curdling and peptonizing milk. Not hydrolyzing starch. Forming indol poorly. Producing NH3 and H2S. Forming acid from dextrose, saccharose, lactose, maltose, glycerin, and mannitol. Optimum temperature of growth is 26°C. The pathogen is kept in the infected seeds collected from infected, but often visually healthy plants. As a latent form, the infection can reproduce from year to year without manifestation of characteristic external symptoms. Under weather conditions the favorable for agent of bacteriosis, such infected seeds can produce diseased plants. Other important sources of bacterial infection are the infected vegetation residues where the pathogen is kept for a long time.
Distribution.Disease is widely distributed in all territories of the former Soviet Union, where the culture is grown; i.e., in the Central Black-Earth zone of Russia (Voronezh, Kursk, Belgorod, Tambov, Lipetsk, Orlov Regions), in the Rostov, Sverdlovsk, Saratov Regions, in the Krasnodar and Stavropol Territories, Kabardino-Balkaria, North Ossetia, and Adygea, and also in Ukraine (Odessa, Mykolaiv, Kirovohrad, Kyiv, Cherkassy, Kharkiv, and other Regions), in Moldova, Kazakhstan, and Belarus.
Ecology.Development of the infection is favored by high temperatures (25-30°C) and RH (90% and more) of air. The maximal manifestation of the bacteriosis (epiphytotics) is promoted by the increased humidity and temperature of air in June and July.
Economic significance.This disease is the most severe bacteriosis of wheat. In nature, the pathogen of Black Chaff of Wheat also attacks rye and barley. This disease can reduce wheat yield by 5-90% depending on a zone of this culture and on favorable weather conditions for the development of the pathogen of bacteriosis. It is found that yield losses may reach 13-34% at 50% affection of surface of flag leaf of wheat, depending on susceptibility of varieties and climatic conditions. The bacteriosis development on winter wheat in conditions of Krasnodar Territory reaches 30% affected plants at distribution to 40-67%. In conditions of the Central Black-Earth zone (Voronezh, Lipetsk, Tambov, and other Regions), distribution of black bacteriosis is 1 to 54% (at development 0.3 to 33.3%) on different varieties of spring wheat. Control measures include optimal agriculture, maintenance of crop rotation, cultivation of relatively resistant varieties, careful removal of plant residues, separating seeds from shrunken grains, treatment of seeds before sowing by pesticides, and treatment of plants by pesticides during vegetation period.
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