Diseases

Plasmodiophora brassicae Woronin - Club Root of Crucifers.

Systematic position.

Class Plasmodiophoromycota, order Plasmodiophorales, family Plasmodiophoraceae, genus Plasmodiophora.

Biological group.

Diseases of rootage of cruciferous crops.

Morphology and biology.

Cysts are spherical, 1.6-4.3 microns in diameter, 3.9 microns on the average; or ellipsoid, ovoid, 4.0-6.0 microns; sometimes compressed, elongated or irregular, 2.5-6.9 microns; with colorless, comparatively thin aciculated coat; usually forming one or a lot of zoospores by germinating period. Primary zoospores are pear-shaped, almost orbicular to oval, 2.5-3.5 microns in diameter; the short flagellum is blunt at the end, the lengthy one is whip-like. Primary spores forming plasmodia are polynuclear, vary in the dimension. Host cells can contain some plasmodia. Zoosporangia are few or numerous (located loosely or in compact aggregations), small, ovoid to almost orbicular and orbicular, 6.0-6.5 microns in diameter, angular or slightly elongated with thin colorless coat. Zoosporangia form 4-8 secondary zoospores of 1.9-3.0 microns in diameter. The short flagellum is 3.4 microns in length, blunt; the lengthy flagellum is whip-like, 11.8 microns in length. The secondary cyst forming plasmodium 100-200 microns in diameter, colorless or pale-gray, amoeboid, sometimes encysted. Primary zoospores formed during germination of cysts penetrate into root hairs and turn into myxamoebae, which quickly increase in the size and transform in polynuclear primary spores forming plasmodia. Subsequently the plasmodium breaks up into zoosporangia. The nucleus of zoosporangium undergoes 2-3 mitoses, and 4-8 zoospores are formed in each zoosporangium. The coat of zoosporangium breaks, and the secondary zoospores migrate from root hairs. After copulation they penetrate through young epidermal cells into root tissue of a host plant and turn there to the two-nuclear secondary cysts forming plasmodium. There is a fast growth and numerous mitotic divisions of the plasmodium's nucleus. A cell division of host plant induces the parasite division. After a while in the secondary plasmodium there is a nucleus karyogamy. After meiosis the plasmodium breaks up into set of the mononuclear haploid amoebas, putting on a coat and turning into sleeping spores (cysts). The disease causes the formation on roots spindle-like, spherical, or irregular swellings, or cecidiums. Infected cabbage seedling with the Club Root on their roots does not usually change the appearance. Only at very early and strong infestation the growth inhibition and yellowing of leaves are observed. Infestation of adult plants' roots causes strong oppression; leaves fade, especially in the afternoon under hot and dry weather, the head develops badly, or it is not formed at all. The type of cabbage seedling's systemic infestation is also described. In this case the plants become chlorotic, lag behind in height; the hypertrophy of latent buds in sinuses of leaves, a proliferation of an apical meristem, formation of cecidiums on leaves and stems are marked. Cecidiums on roots of such plants are observed not always, being much smaller in size, than those on roots of the even-aged plants without systemic infestation. The parasites occur on roots of wild and cultural cruciferous plants. The phytopathogen is also capable to infest some plants from other families, forming zoosporangia and zoospores on the root hairs.

Ecology.

Sleeping spores are preserved in soil more than 3 years. The germination of these spores and infestation of plants are observed at 60-90% soil humidity (min 50%, opt 75-80%). For the infestation sub acidic pH values (5.4-6.5) are optimum. The minimum temperature for successful plants' infestation on acid soils changes in an interval between 10-12.C, maximal - between 30-35.C, optimal - between 20-25.C. At optimal temperatures the increased water delivery promotes the stronger infestation of plants.

Distribution.

The Club Root occurs in Europe, Northern Africa, North and South America, Australia, New Zealand, Japan, Hawaiian Islands. In the former Soviet Union the disease is found in the majority of the European regions. Club Root is marked in the Far East, Siberia, Azerbaijan, and Georgia. The regions of constant and strong Club Root development include Arkhangelsk, Vologda, Kalinigrad, Leningrad, Moscow, Yaroslavl Regions and Karelian Republic; regions of strong, but periodic development are western Regions and northern part of Ukraine; the Club Root weakly develops in Nizhnii Novgorod, Voronezh, Kursk, Samara, and Sverdlovsk Regions. Significant distribution of the Club Root on Volga river's islands in the Saratov and Volgograd Regions and along the river Akhtuba is periodically recorded, the Club Root is marked in individual vegetable gardens in Nikolaevsk-on-Amur, on Sakhalin, in Eastern Siberia, Kemerovo, Tomsk, and Tyumen Regions.

Economic significance.

The disease causes yield losses 10-60% and more. During the strong disease appearance the shortage in cabbage yield on fields infested by the Club Root is 40-50 tons per hectare. Control measures include the following. On small plots, mainly for soil disinfection's indoors, strong disinfectant substances and soil treatments with vapor, electricity, and gamma-rays are applied for the Club Root control. The system of protective measures includes also application of edaphic fungicides with contact and systemic activity, growing of healthy seedlings, strict maintenance of crop rotation, struggle against cruciferous weeds, optimal dates of planting, correct application of organic and mineral fertilizers, usage of resistant varieties, soil liming, optimal water delivery at the artificial sprinkling, addition of a manure and composts under noninfested cultures for 1-2 years before cabbage growing, removing of infested plants' residues from a field.

Related references:

Abdullaev S. 1965. New disease of a cabbage// Kolkh.-sovkh. proizvodstvo Azerbaidzhana. -N. 3.- P. 39 (in Russian).
Arsenyev M.V. 1962. Cabbage Club Root Plasmodiophora brassicae Wor. in Siberia. Izv. Irkutskogo SKHI. -N. 2.-P. 269 (in Russian).
Gerasimov B.A., Osnitskaya E.A. 1961. Pests and diseases of vegetables.-Moscow: Selkhozgiz. -536 p.
Golubintseva A.P. 1958. Club root in Western Siberia. In: Zashchita rastenii ot vreditelei i boleznei. -N. 5.-P. 5 (in Russian).
Ibragimov G.R., Akhmedov S.A. 1966. New dangerous disease of a cabbage in Azerbaijan - Club Root. In: Sb. statei po ovoshchevodstvu. - V. 1.-P. 110 (in Russian).
Ibragimov G.R., Mustafaev B. 1968. Club Root in Azerbaijan. Kartofel. i ovoshchi. -N. 3.- P. 41 (in Russian).
Mazin V.V., Protsenko E.P. 1976. Causing agent of Club Root in cruciferous Plasmodiophora brassicae Woron.- Moscow: Nauka. -192 p. (in Russian).
Nelen E.S., Vasilieva L.N. 1958. The diseases of potato and vegetable cultures in Primorskii Territory and measures for their control.- Vladivostok, -87 p. (in Russian).
Rudenko D.K. 1963. Clubroot. In: Distribution of pests and diseases in agricultural crops in the USSR in 1962 and the forecast of their appearance in 1963. Leningrad: VIZR, -P. 243-247 (in Russian).
Sokolov L.A., Tupenevich C.M. 1974. Club Root of Cabbage. - Leningrad: Kolos, -54 p. (in Russian).
Vladimirskaya M.E. 1971. Club root of cruciferous. In: Methods of the territorial perennial forecast of plant diseases.-Leningrad, -P. 68-69 (in Russian).
Vladimirskaya M.E., Tyuterev S.L., Asyakin B.P. 1986. Methodical instructions on a chemical immunization the white head cabbage for its protection against Club Root and Cabbage Flies. . Leningrad: VIZR, - 18 p. (in Russian).

© Khlopunova L.B.