Clavibacter michiganensis subsp. sepedonicus (Spieckermann et Kothoff) Davis et al. - Ring Rot of Potato.

Systematic position.

Kingdom Procaryotae, section Irregular Nonsporing Gram-positive Rods, family Pseudomonadaceae, genus Clavibacter.


Corynebacterium sepedonicum (Spieckermann et Kothoff) Skaptason et Burkholder.

Biological group.


Morphology and biology.

Cells of Cl. michiganensis subsp. sepedonicus are short (straight or bent), often rounded rods, single or V- and Y-shaped, settling in pairs or chains, usually 0.3-0.8 x 1.0-1.4 mkm in size. Not having flagella. Aerob. Gram-positive. On nutrient mediums, colonies grow very slowly, being round, smooth, poorly raised, opaque, brilliant. Their color is white, cream to yellow. Not diluting gelatin or diluting gelatin very poorly. Curdling milk (some strains peptonize). Reducing litmus milk. Oxydase and urease reactions are negative. Hydrolyzing starch poorly. Not reducing nitrates. Not producing NH3 and indole. Forming H2S in insignificant amounts. Not hydrolyzing casein. Utilizing acetate. Hydrolyzing esculin. Producing acid on sorbitol, but not producing it on inulin and ribose. Optimum temperature for growth is 20-23°C, maximum 30-31°C, minimum 3-4°C. The Ring Rot of Potato appears on tubers and adult plants. Vascular ring is usually attacked in tubers. At first stage of the disease development, the ring has a bright cream color, then turns yellow and brown. The bacteriosis attacks the vascular system of the plant, infecting it slowly; therefore, the first symptoms are frequently shown during flowering, especially in damp cold years. The disease may have latent form. The infected plants wilt, with their leaves becoming yellow, covered with spots, braided, and drying up. Diseased plants often lag behind in growth, become dwarfish, with short internodes and close arrangement of leaves. The main sources of the infection are diseased tubers and the vegetation residues.


The Ring Rot of Potato occurs in the USA, Canada, Venezuela, Germany, Finland, France, Austria, Denmark, England, Poland, Belgium, Czechoslovakia, Cambodia, Vietnam, Nepal, and other countries of the world. It is widely distributed in all territories of the former Soviet Union where this culture is growing; i.e., in the Russian Federation, and also in Belarus, Latvia, Armenia, Kazakhstan, Kirghizia, and Ukraine.


Optimum development of bacteriosis on plants is favored with warm damp weather during the first half of their vegetation. Bacteriosis causes the greatest severity in areas with adequate high temperatures; the optimum temperature for pathogen is 21-27°C in droughty years. During adverse weather conditions, the bacterial infection is capable of passing from seed tubers through stolons to young tubers where it may remain in latent form until the following vegetation period. Optimum temperature for distribution of this disease is 21-26°C.

Economic significance.

Severity of the Black Leg of Potato consists in lesion of landing tubers and plants during vegetation, and also in rotting of tubers during storage of yield. The severity of this bacteriosis is especially high in storehouses during long storage periods, if the tubers have infected with internal infection of the pathogen. Yield losses depend on a cultivated variety. In some farms of the Moscow Region, the amount of diseased plants reaches 15-30% under favorable conditions for the bacteriosis, and the amount of infected tubers reaches 8-12% during storage time. In different climatic areas of Belarus, the amount of diseased bushes varies, depending on the resistance of varieties. Within the limits of 0.4-3.8%, the amount of infected tubers having symptoms reaches 4%, and the amount of tubers with latent infection of bacteriosis exceeds 20%. However, on some fields of this country, about 30% of diseased plants are observed during epiphitotics. Control measures include optimum agriculture, maintenance of crop rotation, selection of resistant varieties, careful destruction of the vegetation residues, seed treatment by pesticides before landing, and pesticide treatment of plants during the vegetation period.

Reference citations:

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Bushkova L.N., Avezdzhanova G.P. 1968. The distribution of diseases of agricultural crops in the USSR in 1967. In: Polyakov I.Ya., Chumakov A.E., eds. Pests and diseases distribution on agricultural
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Davidchik L.Ya. 1987. About distribution and semiology of bacterial diseases in Latvia. In: Samersov V.F., ed. Protection of agricultural plants in conditions of application of intensive technologies. Abstracts of reports of research-and-production conference. Minsk: Belaruskoe Republikanskoe pravlenie NTO sel.skogo khozyaistva. Part 2. p. 124-125 (in Russian).
Davidchik D.Ya., Khodos S.F. 1990. Bacterial diseases of potato and their pathogens in Latvia. In: Gvozdjak R.I., ed. Materials of conference. Phytoncides. Bacterial diseases of plants. Part II. Kiev & Lvov: KGT-2, p. 71 (in Russian).
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Murzakova K.F. 1966. The immunological features of Corynebacterium sepedonocum (Spiecrermann et Kotthoff) Skaptason et Burkholder and of ring decay of potato caused. PhD Thesis. Moscow, 15 p. (in Russian).
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© Lazarev A.M.

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