Diseases

Cercospora beticola Sacc. - Cercospora Leaf Spot

Systematic position.

Class Ascomycota, order Sordariales, family Laesiosphaeriaceae, genus Cercospora (=Pseudocercospora).

Biological group.

It is a facultative saprotroph.

Morphology and biology.

Beet leaves of the first and second year of growth are mainly affected; on parent plants the disease can develop on petioles, stalks, and seed gloms of beet. Round light-brown spots are formed on older leaves, 2-3 mm in diameter, having reddish or brownish rim. Spots on old dying leaves are very large, 5-10 mm in diameter, with obscure indistinct light-brown rim. Oblong, slightly pressed spots are formed on petioles and stalks of seed beet, similar to those on leaves. Velvety grayish-white bloom of fungus sporification appears in damp weather at spots on the lower and upper sides of a leaf and on other affected organs. Conidiophores are light brown, are geniculately bent, appearing on surface of affected organs one by one at first, and in bunches later. Their size is 30-135 x 4-5 microns. Colorless, obclavate or nearly acicular conidia, having 3-5 or more septa and 30-36 x 3-5 microns in size, appear at the ends of conidiophores. Affected plants demonstrate an increase in transpiration rate by 3-4 times, a decrease in assimilation of carbonic acid; and nitrogen metabolism is disrupted. Strongly affected leaves die off, and the plant forms new leaves which cause a reduction in root weight and saccharinity. The disease affects about 40 species of plants belonging to 26 genera (lucerne, peas, soy, potato, etc., and wild-growing plants, such as amaranth, goose-foot, mallow, sow-thistle, etc.) in addition to all species of beet.

Distribution.

The Cercospora Leaf Spot is found in all areas of beet-growing in the former USSR. The areas of highest severity (to 70-100% or 3rd point) are found in the Krasnodar and Stavropol Territories, Kyrgyzstan, and Kazakhstan. The areas of moderate severity are recorded in the western beet-growing areas of the Ukraine, in Latvia, Lithuania. Its areas of low severity are found in the eastern areas of Ukraine, in Central Black Earth areas of Russia, in the Volga River region, in Byelorussia, Moldova, and Siberia.

Ecology.

The fungus winters in dead organs in the form of thickened dark-colored hyphae (stromata) in the top layer of the ground (5-10 cm deep). The fungus develops in a wide range of temperatures, from 5 to 35 degrees C (optimum is 19-30 degrees C), with a relative air humidity of 70% and more. The incubation period lasts 10-13 days during the summer months and 30-40 days in autumn.

Economic significance.

The disease results in reduction of productivity of root crops by more than 50%. Saccharinity is considerably reduced by 3 to 7%. This results in losses of sugars (to 60-70%). Control measures are as follows: agronomical actions include crop rotation; technique for preservation of moisture in ground (deep autumn plowing, retention of snow on fields, pre-seeding treatment of ground, loosening, weeding); application of fertilizers (potash especially) and top dressing of plants by fertilizers and microelements after thinning and before plant canopy closure; spraying and dusting by fungicides; use of resistant varieties.

Reference citations:

Amanzholov A.A. 1980. Fungal diseases of seed sugar beet in Kazakhstan and their control. PhD Thesis. Alma-Ata: KazakhSKHI. 18 p. (In Russian)
Gorlenko M.V. 1980. Phytopathology. Leningrad: Kolos. 318 p. (In Russian)
Hawksworth D.L., Kirk P.M., Sutton B.C., Pegler D.M. 1995. Ainsworth & Bisby.s Dictionary of the fungi. CAB International. 616 p.
Popova I.V. 1968. Diseases of sugar beet. In: Polyakov I.Ya., ed. 1968. Distribution of pests and diseases of grown crops in the USSR in 1967 and the forecast of their appearance in 1968. Moscow: Rossel.khozizdat. 94-96 p. (In Russian)
Popova I.V. 1969. Diseases of sugar beet. In: Polyakov I.Ya., Chumakov A.E., eds. Distribution of pests and diseases in agricultural crops in the RSFSR in 1968 and the forecast of their appearance in 1969. Leningrad: VIZR. 116-119 p. (In Russian)
Pozhar Z.A. 1963. Diseases of sugar beet. In: Polyakov I.Ya., Chumakov A.E., eds. Distribution of pests and diseases in agricultural crops in the USSR in 1962 and the forecast of their appearance in 1963. Leningrad: VIZR. 218-225 p. (In Russian)
Rakhimbekova A.K. 1975. Features of development of Club Root of Sugar Beet in Kazakhstan. In: Zubenko V.F., ed. Effective methods of sugar beet protection from diseases at industrial technology of its cultivation. Kiev: VNIS. 156-160 p. (In Russian)
Salunskaya N.I. 1959. Cercospora Leaf Spot. In: Savchenko E.N., ed. Beet growing. Kiev: VNIS. 413-431 p. (In Russian)
Zhorzhesko G.G. 1985. Features of development of Club Root of Sugar Beet in Krasnodar Territory. In: Zubenko V.F., ed. Effective methods of sugar beet protection from diseases at industrial technology of its cultivation. Kiev: VNIS. 11-17 p. (In Russian)

© Khlopunova L.B.