Diseases
Fusarium spp. Lk:Fr, Rhizoctonia spp. DC. - Root Rot of Cucumbers
Systematic position.
Fusarium spp. - division Ascomycota, order Hypocreales, family Hypocreaceae. Rhizoctonia spp. - division Mitosporic Fungi (traditional class Agonomycetes (Mycelia sterilia).Biological group.
Facultative parasites.Morphology and biology.
The Root Rot of Cucumbers is spread in both protected and open ground, appearing during all period of vegetation. The disease is complex, resulting from adverse conditions of cultivation that weaken plants and therefore promote development of soil parasitic pathogens. The main agents of the disease are fungi of the genera Fusarium (F. oxysporum, F.solani etc.) and Rhizoctonia (R.aderholdii). On affected seedlings the fusariosis causes darkening of root neck and root, thinning of stalk, withering of cotyledonous and young leaflets, and dying of the plant. In older plants the leaves turn yellow, bark of the lower part of stalk and root grows brown, stalks fray, and the plant withers and dries. The root has well visible brownish vessels with developed fungal mycelium. The mycelium is web-like, white, with pink or yellowish tint. Conidiophores are well pronounced, simple or ramified. Macroconidia are formed on simple or ramified conidiophores, being usually crescent with various extent of curvature, having 3-5 septae. Microconidia are numerous, formed on long cylindrical conidiophores, having oval-cylindrical shape, 10.8-18.6 x 1.5-3 mkm in size. Chlamydospores uni- or bicellular, colorless. Affected by Rhizoctonia plants have rotted root neck of shoots; the plant top droops; leaves shrink, bend, grow brown, and dry up. Mycelium forms fine-felt brown bloom and fine dark-brown sclerotia of irregular shape. Series of thickened indecomposable cells are sometimes formed on hyphae (5.5-9 mkm).Distribution.
The Root Rot of Cucumbers is distributed everywhere in zone of the culture cultivation. The greatest harm the disease causes in protected ground of Northwest and Central Regions, in Krasnodar Territory, Western and Eastern Siberia, and the Far East. Outside Russia it is known in Baltic States, Moldova, Ukraine, Transcaucasia, and Central Asia.Ecology.
The fusariosis agents develop at optimum temperature 18-27.C (minimum 10.S, maximum 35.C); optimum air humidity is 40-70%, optimum soil pH is 4-7. Chlamydospores are a source of the infection, keeping in affected vegetation residues and in ground. Development of Rhizoctonia is promoted by sharp daily fluctuations of temperature, prolonged downturn of temperature (below 13.C), by high soil (80% and higher) and air humidity (90-95%), by lack of illumination, and by soil pH 5-7.6. Sclerotia are a source of the infection, keeping in affected vegetation residues.Economic significance.
Incorrect conditions of cucumber cultivation promote the disease high severity, resulting in destruction of shoots by 60-80%, and decrease of yield by 23-38%. Protective actions include cleaning and destruction of vegetation residues; maintenance of crop rotation (return of gourds on a former field in 4-5 years); disinfection of soils, hotbeds and hothouses; escaping sharp fluctuations of air, ground and water temperature (the water temperature is not lower than 20.C, the ground temperature is not lower than 20-22.C); dressing of seeds before sowing; introduction of resistant varieties.Related references:
Grin.ko N.N. 2002. Specific structure of agents of Root Rot of Cucumbers in protected ground. Vestnik Rossiiskoi akademii sel.skokhozyaistvennykh nauk 5: 55-57 (in Russian).Hawksworth, D.L., Kirk, P.M., Sutton, B.C. & Pegler, D.N. 1995. Ainsworth and Bisby's Dictionary of the fungi. 8th edition. Kew, Surrey: Commonwealth Mycological Institute. 616 p.
Karbozova R.D. 1993. Root Rot of Cucumbers in protected ground and its control. PhD Thesis, Almaty: Kaz.SKHI, 21 p. (in Russian).
Lopukhina G.P., Antonov Yu.P., Blinova Z.P., Kosacheva R.Z., Yaremko T.N. 1977. Diseases of vegetable cultures. In: Polyakov I.Ya., Semenov A.Ya., Zakharova T.I., eds. Pests and diseases distribution on agricultural crops in RSFSR in 1976 and the forecast of their appearance in 1977. Moscow: MSKH RSFSR, GUZR, VIZR, p. 217-232 (in Russian).
Lyiveke Kh.M. 1972. Distribution and agents of fusariosis of Cucumbers in protected ground of Estonia and its control. PhD Thesis, Tallin: Est. SKHA, 40 p. (in Russian).
Marzhina L.A., Nikolaeva S.I., Kharbur M.V. 1984. Fusariosis of Cucumbers in protected ground and its control. In: Filippov N.A., ed. Microbiological method of plant diseases and pests control. Kishinev: Shtiintsa, p. 64-69 (in Russian).
Osnitskaya E.A. 1968. Diseases of vegetables. In: Polyakov I.Ya., Chumakov A.E., eds. Pests and diseases distribution on agricultural crops in RSFSR in 1967 and the forecast of their appearance in 1968. Moscow: Rosselkhozizdat: 120-125 (in Russian).
Osnitskaya E.A. 1969. Diseases of vegetables. In: Polyakov I.Ya., Chumakov A.E., eds. Pests and diseases distribution on agricultural crops in RSFSR in 1968 and the forecast of their appearance in 1969. Moscow: Rosselkhozizdat: 137-144 (in Russian).
Osnitskaya E.A. 1970. Diseases of vegetables. In: Polyakov I.Ya., Minkevich I.I., eds. Pests and diseases distribution on agricultural crops in RSFSR in 1969 and the forecast of their appearance in 1970. Moscow: MSKH RSFSR, VIZR: 252-263 (in Russian).
Osnitskaya E.A. 1971. Diseases of vegetables. In: Polyakov I.Ya., Minkevich I.I., eds. Pests and diseases distribution on agricultural crops in RSFSR in 1970 and the forecast of their appearance in 1971. Moscow: MSKH RSFSR, VIZR: 187-198 (in Russian).
Ragimov U.A., Bagirova Sh.G. 1977. Fusariosis of Cucumbers and its control in Kirovabad Hothouse Combine. In: Vasilyan V.V., ed. Abstracts of the eighth session of the Transcaucasian council on coordination of research works on plant protection (December, 14-16, 1977). Erevan: Arm.NIIZR, p. 183-184 (in Russian).
Zemite A.F. 1971. Distribution and specific structure of Root Rot of Cucumbers in protected ground of Latvia. In: Vimba E.K., ed. Materials of 7th symposium mycologists and lichenologists of Baltic republics. Riga: Latv.GU, Prib.fil. VIZR, Latv. otd. VBO, p. 176-177 (in Russian).