Diseases

Botrytis cinerea Pers., Fusarium spp. Li: Fr., Rhizopus nigricans Ehrenb. - Clamp Rot of Sugar Beet

Systematic position.

Botrytis cinerea - Division Ascomycota, order Leotiales, family Sclerotiniaceae, genus Botrytis.
Rhizopus nigricans - Division Zygomycota, order Mucorales, family Mucoraceae, genus Rhizopus.
Fusarium spp. - Division Deuteromycota, order Moniliales, family Tuberculariaceae, genus Fusarium.

Morphology and biology.

Clamp Rot develops during storage of roots of parental and commercial beet in clamps and during temporary field storage of roots in heaps. Process of root rotting proceeds due to the activity of a complex of microorganisms. One of the active infecting agents is hygrophilous fungus, Botrytis cinerea (activator of Gray Rot). On the affected tissue it forms fluffy gray mycelium having dendritic conidiophores, with numerous ovoid-ellipsoid conidia being 9-15 x 6.5-10 microns in size. Under adverse conditions the fungus forms black irregular-shaped sclerotia having warty surface and a size of 2-7 mm. As a result, the root tissue loses durability, decaying easily. Teleomorph is represented by Botryotinia fuckeliana (DB). Whet., B. ranunculi Henneb. et Grov., B. ficariarum P. Henn. Fungi of the genus Fusarium, such as F. oxysporum and F. solani, are also active agents of Clamp Rot, forming white or pink mycelium on rotting roots. Conidiophores are well pronounced, simple or ramified. Macroconidia are formed on simple or ramified conidiophores, being usually crescent, variously curved, with 3-5 septa. Microconidia are formed on long cylindrical conidiophores, numerous, oval-cylindrical, 10.8.18.6 x 1.5.3 microns. Chlamydospores are numerous, one- or two-celled, colorless. Fusarium fungi frequently affect beet roots in field during beet vegetation and then continue their development in clamps. Thermophilic Rhizopus nigricans spreads quickly in clamps at increased temperatures (under self-warming of beet clamps or at high air temperatures in early period of storage in southern areas of beet-growing). Fungal mycelium form on surface of roots, being crumbly-pannose, olive-brownish-gray. Rhizoids are ramified, dark brown. Stylosporangiophores are 500-3000(4000) x 10-35 microns in size, arising by 2-5 from rhizoidal neck. Sporangiophores are ellipsoid-spherical, 4-12(16) x 4-10(12) microns in diameter. During its vital activity R. nigricans can decompose sugar, causing alcoholic fermentation. R. nigricans together with B. cinerea causes faster rotting of roots than each of them separately. Activators of the disease affect more than 150 plant species of the families Asteraceae, Solanaceae, Fabaceae, Apiaceae, etc.

Distribution.

Clamp Rot of Sugar Beet is distributed everywhere in the zone of sugar beet cultivation. The activator of Gray Rot is found in the Ukraine and Central-Chernozem region of Russia; Fusarium is known in the Northern Caucasus, Central Asia, and Transcaucasia; R. nigricans is recorded in Central Asia. These areas belong to the zone of high severity of the Clamp Rot (where up to 30-90% of roots are affected).

Ecology.

B. cinerea is a specific clamp microorganism, typical aerobe, developing at temperatures of 4 to 42.C (optimum is 25-30.C) and relative air humidity at about 100%. Activators of fusariosis develop at optimum temperatures of 18-27.C (minimum 10.C, maximum 35.C); optimum air humidity is 40-70%. R. nigricans develops at temperatures of 5 to 45.C (optimum is 30-35.C), and is not demanding to oxygen in the air. The infection keeps in ground, on vegetation residues and roots.

Economic significance.

Loss of root weight can reach 17.9% and loss of sugar can be 1.74 to 9.23% depending on the manner of sugar beet storage in field clamps; up to 25-36% of parental roots perish as a result of Clamp Rot in seed-growing farms; it is practically impossible to produce white crystal sugar from sugar beet that is affected by the Rot greater than 10-12%. Protective actions include heavy application of fertilizers; protection of beet against pests and diseases during vegetation; protection against drying during harvest; preservation of roots from mechanical damage at harvesting, transportation, and reloading; protection of roots against subfreezing; careful rejection of roots before stacking in clamps; treatment of clamp fields with lime; periodic survey of stored roots and removal of rotting roots; maintenance of thermal regime in clamps (1-2.C).

Reference citations:

Al.khovskaya T.F. 1969. Fungal diseases of sugar beet in Chu River valley of Kyrgyzstan. PhD Thesis. Tashkent: AN UzbSSR. 19 p. (In Russian)
Bilai V.I., ed. 1988. Microorganisms . agents of plant diseases. Kiev: Naukova dumka. 550 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.
Kornienko A.S., Barshtein L.A., Prikhodchenko S.S., Pyatkovskii N.K., Kovbasyuk E.V., Zemlyanoi A.I. 1985. Significance of agronomical measures of sugar beet cultivation for increase of its efficiency and resistance of roots against Clamp Rot. In: Zubenko V.F., ed. Effective measures of sugar beet protection against diseases at industrial technology of its cultivation. Kiev: VNIS. 64-70 p. (In Rus sian)
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)
Prikhodchenko S.S., Kornienko A.S. 1985. Peculiarities of long commercial storage of sugar beet in connection with manner of its harvesting. In: Zubenko V.F., ed. Effective measures of sugar beet protection against diseases at industrial technology of its cultivation. Kiev: VNIS. 141-143 p. (In Russian)
Shevchenko V.N. 1959. Clamp Rot of Sugar Beet. In: Savchenko E.N., ed. Beet Growing. V. 3. Kiev: Ukrsel.khozgiz (VNIS). 523-538 p. (In Russian)
Toporovskaya Yu.S. 1975. Peculiarities of development of mycoflora of Clamp Rot of Sugar Beet in connection with conditions of commercial storage of roots. In: Zubenko V.F., ed. Effective measures and manners of sugar beet protection against diseases. Kiev: VNIS. 138-146 p. (In Russian)

© Khlopunova L.B.