Diseases

Peronospora schachtii Fuck. - Downy Mildew of Sugar Beet.

Systematic position.

Division Oomycota, order Peronosporales, family Peronosporaceae, genus Peronospora.

Biological group.

Highly specialized obligate parasite.

Morphology and biology.

Plants of the first year and parent plants are affected. On plants of the first year the young central leaves of the socket turn yellow; their edges curve downward, thicken, and become fragile. On plants of the second year in the beginning of vegetation the youngest leaves of the central or peripheral buds, and then top floriferous shoots, bracts, flowers, and even seed glomes are affected. Affected floriferous shoots bend, lag behind in growth, and die off. Grayish-violet bloom of fungal mycelium is formed in damp weather on the lower side of leaves and other affected organs. Conidiophores leave stomata by 2-3 ones, being 6- or 8-times dichotomously ramified. Conidia ovoid, 21-27 x 16-20 microns, with thin grayish-violet coat. Oospores are formed on younger leaves and seed glomes; they are spherical, light yellow, brown at ripening, with thick two-layer coat. Mangel and red beet are affected in addition to sugar beet.

Ecology.

The fungus develops at temperature 8 to 30.C (optimum is 15-17.C) and relative humidity 70% and higher. The incubation period lasts 5-20 days. Winters as oospores in heads of parent roots mainly, and also in vegetation residues and in seed glomes.

Distribution.

Peronosporosis is widely distributed and very nocuous in the countries of Western Europe, being known more than 150 years. In the former USSR the first record of the disease was marked in 1915, exhibiting periodically weak development in some farms prior to the beginning of the 1940-s. Now the peronosporosis is found in all beet-growing areas.

Economic significance.

The disease results in deformation of roots and deterioration of their quality, in reduction of yield of roots by 50%, of seeds by 65%, of sugar by 30%. Protective actions are maintenance of spatial isolation between fields of parent and seed beet (not less than 1 km); seed dressing before seeding, spraying of crops by fungicides; culling of diseased roots harvested for parent plantations; removing of vegetation residues, deep plowing; cultivation of resistant varieties.

Related references.

Al.khovskaya, T.F. 1969. Fungal diseases of sugar beet in Chu River valley of Kirghizia. PhD Thesis. Tashkent: ANUzbSSR, 19 p. (in Russian)
Batalova, T.S., Shevchenko, V.N., Pozhar, Z.A., Tishchenko, E.I. 1973. Diseases of sugar beet. In: Chumakov, A.E., ed. Distribution of diseases in agricultural crops in the USSR in 1968-1972. Leningrad: VIZR. p. 77-80 (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, p. 94-96. (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. p. 116-119. (in Russian)
Popova, I.V. 1971. Diseases of sugar beet. In: Polyakov, I.Ya., Minkevich, I.I., eds. Distribution of pests and diseases in agricultural crops in the RSFSR in 1970 and the forecast of their appearance in 1971. Moscow: VIZR, p.148-154 (in Russian)
Popova, I.V., Zlotnikov, M.D. 1970. Diseases of sugar beet. In: Polyakov, I.Ya., Minkevich, I.I., eds. Distribution of pests and diseases in agricultural crops in the RSFSR in 1969 and the forecast of their appearance in 1970. Moscow: VIZR, p.205-212 (in Russian)
Pozhar, Z.A. 1959. Downy Mildew. In: Savchenko, E.N., ed. Beet Growing. V. 3. Kiev: Ukrsel.khozgiz (VNIS), p. 438-450. (in Russian)
Pozhar, Z.A. 1961. Diseases of sugar beet. In: Polyakov, I.Ya., Chumakov, A.E., eds. Distribution of pests and diseases in agricultural crops in the USSR in 1960 and the forecast of their appearance in 1961. Leningrad: VIZR. p. 144-1472 (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. p. 218-225. (in Russian)
Pozhar, Z.A. 1964. Diseases of sugar beet. In: Polyakov, I.Ya., Chumakov, A.E., eds. Distribution of pests and diseases in agricultural crops in the USSR in 1963 and the forecast of their appearance in 1964 (Proc. VIZR, V, 22). Leningrad: VIZR. p. 272-282 (in Russian)
Pozhar, Z.A., Tishchenko, E.I., Popova, I.V. 1978. Diseases of sugar beet in 1977 and 1978. Sakharnaya svekla 3: 31-33 (in Russian)
Pozhar, Z.A., Tishchenko, E.I., Popova, I.V. 1979. Diseases of sugar beet in 1979. Sakharnaya svekla 4: 36-38 (in Russian)

© Khlopunova L.B.