Diseases

Verticillium dahliae Kleb. - Sunflower Verticillum Wilt.

Systematic position.

Class Deutoromyces, order Hyphomycetales, genus Verticillium.

Biological group.

Facultative parasite.

Morphology and biology.

V.dahliae in its life cycle forms septate colorless mycelium with verticillate conidiophores; sterigmas of the conidiophores form hyaline monocellular conidia in their heads. Inside the affected tissue the fungus forms microsclerotia up to 0.1 mm in size. Remaining in soil for several years, microsclerotia are the basic source of infection by causative agent. Pathogen is also spread with the help of infected seeds. The fungus V.dahliae, being a polyphage, affects numerous cultural and wild plants in addition to sunflower. First symptoms of affection of sunflower are visible on lower leaves in a phase of anthodium formation beginning as necrotic mosaic. At first some parts of leaves between veins lose turgor, becoming pale green or yellowish. Later the disease spreads up to top leaves. Necroses on the leaves become red-brown. Affected leaves become completely dry. Occurrence of the indicated symptoms is connected with affection of conducting vessels, petioles of leaves and stalks, and their internal tissue becomes dark brown.

Distribution.

Verticillum Wilt is spread in Russia and other countries of the former USSR on sunflower everywhere.

Ecology.

The causative agent affects sunflower more intensively under dry and hot conditions. Some researchers specify that the pathogen causes the maximal yield loss on lighter soils.

Economic significance.

Yield loss of sunflower affected by the pathogen may reach 55%. It causes the greatest harm in Northern Russia, the Caucasus, the Volga Basin region (Saratov and Volgograd Regions), Kazakhstan, southern provinces of Ukraine and Moldova. Control measures against the disease include resistant varieties and hybrids, rotation of sunflower, presowing treatment of seeds, and least favorable, systemic fungicides.

Related references:

Kukin V.F. 1982. Diseases of sunflower and their control. . Moscow: Kolos, 80 p. (in Russian).
Tikhonov O.I. 1975. Diseases of sunflower. In: Pustovoit V.S., ed. Sunflower. Moscow: Kolos, p. 401-409 (in Russian).
Tselle M.A. 1932. Diseases of sunflower. Leningrad: USU OBV, p. 10-13 (in Russian).
Yakutkin V.I. 2001. Diseases of sunflower in Russia and their control. Zashchita i karantin rastenii 10: 26-29 (in Russian).

© Yakutkin V.I.