Diseases

Erwinia carotovora subsp. atroseptica (van Hall) Dye - Black Leg (Soft Rot) of Potato.

Systematic position.

Kingdom Procaryotae, section Gram-negative aerobic rods and cocci, family Enterobacteriaceae, genus Erwinia.

Synonyms.

Bacillus atrosepticus van Hall, Erwinia atroseptica (van Hall) Jennison, B. atrosepticum (van Hall) Lehmann & Neumann, Erwinia phytophthora (Appel) Holland, Pectobacterium atrosepticum (van Hall) Patel & Kulkarni,Pect. carotovorum var. atrosepticum Hellmers & Dowson, B. carotovorum var. atrosepticum (Jones) Hellmers & Dowson, Pectobacterium phytophthorum (Appel) Waldee, E. carotovora var. atroseptica (Hellmers & Dowson) Dye.

Biological group.

Hemibiotroph.

Morphology and biology.

The Black Leg of Potato attacks tubers and plants during vegetation. It is also shown as rotting of tubers during yield storing. The radical part of plant stems (more often in seedlings) rots and gets various colors (from yellow-brown to black). Such stems lag behind in growth. Their leaves turn yellow and become chlorotic. The top leaves are fine, rigid, rolling around central rib. Diseased stems grow upward at the sharp angle, easily separating from the parent tuber. The Bacteriosis is shown on infected tubers as rotting (soft rot) of core at stolon mainly (less often in places of the infection introduction) that causes, as a rule, destruction of the bush. This diseased pulp is dark-brown to black, smelling sharply and unpleasantly. Healthy tubers may be infected by mechanical contact with the diseased ones (during vegetation and harvesting). The diseased vegetation residues and tubers are sources of the bacterial infection. Cells E.carotovora subs. atroseptica are straight bacilli, usually 0.5-1 x 1.3 mkm, moving by means of peritrichous flagella. Gram-negative. On potato agar, colonies are bluish, convex-flat, rounded, with rough borders. On Logan.s media, they are light-blue, in big bowl-shaped cavities. Diluting gelatin. Not hydrolyzing starch. Excreting H₂S and NH₃. Not forming indole. Reducing litmus milk; some strains peptonizing milk. Oxidaze test is negative. Reducing nitrates. Catalase test is positive. Having no urease. Excreting acid on mediums with carbohydrates. Having pectolitic enzymes. Optimum temperature for growth of bacteria is 24-28°C, maximum 37°C.

Distribution.

The Black Leg (Soft Rot) of Potato meets in all countries of the world. It is widely distributed in all territory of the former Soviet Union where this culture is growing.

Ecology.

Development of the Black Leg of Potato depends on combination of some abiotic factors (temperature, relative humidity of air, amount of precipitations, etc.). These factors determine also the length of incubatory period during the bacteriosis development. The bacteriosis causes the greatest severity in areas with rather high temperature (optimum temperature for the pathogen is 21-27°C) and under long damp weather conditions (especially at sufficient precipitations and high air humidity, more than 50%). Under adverse weather conditions, the bacterial infection is able to pass from seed tubers through stolons to young tubers and to be kept there in the latent form till the following vegetation period. Optimum temperature for this disease spread is 21-26°C. The bacteriosis severity is especially high in storehouses, where the storing tubers infected with the internal infection of pathogen are kept for a long time.

Economic significance.

The pathogen of bacteriosis attacks a lot of both cultural and wild-growing species of plants of various families. Severity of the Back Leg of Potato consists in lesion of landing tubers and vegetating plants, and also in rotting of tubers during yield storing. Yield losses depend also on a cultivated variety. In the North-Western zone of Russia (Leningrad Region), the amount of infected plants varies depending on presence of surface or internal infection (from 6.5-7.5 to 30-65%). The lesion of stems and tubers by the pathogen grows at subsequent reproductions of potato. Thus, in epiphytotic 1979 the amount of diseased young plantings and tubers (the variety Stolovyi 19) reached 7.5% in superelite, 22.5% in elite, and 35.7% in the first-reproduction plants. In Primorskii Territory and in the south of the Kamchatka Region, the disease attacked 3-10% and 15-20% of bushes, and during epiphytotics - 80% and 40%, accordingly. There were 16-20% of infected plants in Belarus in epiphytotic years; storage losses caused by the Black Leg and Soft Rot varied from 10 to 30% (or 25-80%, counting the latent form). The amount of diseased plants sometimes reached to 30% in Lithuania. In Latvia, the Black Leg attacked 20-23% of plants in elite plantings; more than 5% of tubers were diseased at storage (to 40%, counting the latent form). In Georgia, the amount of infected plants was 1.5-5% during vegetation, about 2-5% of tubers during storage. In Kirgizia, in some years, the Black Leg attacked about 5-8% of plants (depending on susceptibility of varieties). Control measures include a complex of various agronomical actions, which should be directed to cultivation of healthy plants. These are maintenance of crop rotation, selection of resistant varieties, correct application of mineral fertilizers, pesticide treatment of plants during vegetation, careful destruction of the vegetation residues. Control of carriers of bacteria and of weeds as reservations of bacterial infection is important. It is necessary to use highly sensitive serological methods for early diagnostics of seed infection by the pathogen.

Reference citations:

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© Lazarev A.M.