Diseases

Athelia rolfsii (Curzi) C.C.Tu and Kimbr. - Basal Stem Rot or Southern Blight of Sunflower.

Systematic position.

Kingdom Fungi, phylum Basidiomycota, class Basidiomycetes, order Atheliales, family Atheliaceae, genus Athelia

Synonyms.

Sclerotium rolfsii Sacc., Pellicularia rolfsii (Curzi) E.West. (http: // www.SpeciesFungorum.org ).

Biological group.

Saprotroph.

Morphology and biology.

Having the fungal causative agent Athelia rolfsii, the Basal Stem Rot of sunflower appears in the form of brown necrosis on the ground part of stalks and roots. The pathogen in its life cycle develops teleomorpha stage [Hypochnus centrifugus (Lev.) Tul.], which has not been found yet in the former USSR. During the ontogeny process, the fungus forms white cellular thick septate mycelium and small spherical (0.5 to 3 mm in diameter) sclerotia of light to dark-brown color. Tussocky hymenium with basidia is formed on a thin layer of mycelium, first brightly brown and then gray color. Fruit bodies are obovate basidia with sterigmas forming elliptic, colorless smooth spores. Sources of the infection are sclerotia in soil and mycelium on the affected residues. The causative agent is polyphagous, affecting about 200 species of plants. In the countries of the former USSR, the Basal Stem Rot of sunflower is not thoroughly explored.

Distribution.

The disease is registered in Krasnodar Territory of Russia in some foci (Yakutkin, 2005). It may likely occur in Ukraine and Moldova.

Ecology.

The disease is confined to warm and moist territories, with daily average air temperature in the limits of 30-33°C (Maric et al., 1987). In arid zones it manifests in irrigated sites.

Economic significance.

Affected plants wilt and dry up. Sunflower yield loss caused by the disease may reach 11% (Siddique et al., 1985). Control measures are crop rotation, plowing-in of the affected residues, use of less susceptible varieties and hybrids, and pre-sowing treatment of seeds.

Reference citations:

Maric A., Camprag D. & Masirevic S. 1987. Sunflower diseases and pests and their control. Belgrade: Nolit, 379 p. (in Serbian).
Siddique M.M., Khokhar L.K. 1985. Occurrence of sunflower collar rot diseases caused by Sclerotium rolfsii in Pakistan. FAO, Helia, 1, p.10-14.
Yakutkin V.I. 2005. Diseases of sunflower. In: Pavlyushin V.A., ed. Diseases of cultural plants. Saint Petersburg: VIZR, p 60-67 (in Russian).

© Yakutkin V.I.

Picture © Frolov A.N.