Diseases

Tilletia caries (DC.) Tul., Tilletia laevis Kuehn - Common bunt (Stinking smut, Bunt smut, Covered smut).

Systematic position.

Class Basidiomycetes, subclass Teliobasidiomycetidae (= Sclerobasidiomycetidae), order Ustilaginales, family Tilletiacea, genus Tilletia. Two closely related fungi Tilletia caries and Tilletia laevis cause Common bunt.

Synonyms.

Tilletia caries (DC.) Tul. = Tilletia tritici (Bjerk.) G. Winter; Tilletia laevis Kuehn = Tilletia foetida (Wallr.) Liro

Biological group.

Obligate wheat pathogen.

Morphology and biology.

T. caries and T. laevis have similar biological and cytological characteristics and disease symptoms. Species are distinguished by morphology of the teliospores: they are reticular in T. caries smooth-walled in T. laevis. The fungi are found as teliospores on seed surface. After sowing of wheat the teliospores germinate on seeds (or on soil in dry areas), forming a basidium (promycelium) containing haploid basidiospores. The basidiospores fuse to form dicaryotic hyphae that infect young wheat seedlings. Mycelium becomes systemic and advances with the terminal meristem (growing point). Mycelia invade the developing ovary and replace the tissue that would normally form in the pericarp. Infected plants are shorter than normal plants because of shortened internodes and infected heads are bluish green when they emerge from the boot. Infected heads also maintain a greenish color longer and, in addition, they are more slender than normal heads. The mycelium of pathogen then splits off into dark, thick-walled fragments that develop into teliospores and a bunt ball is created. Disease is apparent when the wheat heads. Crushed seeds discharge grayish liquid having trimethylamine odor (fishy odor) that gives rise to the "stinking smut" name for this disease. Bunt balls are easily ruptured during harvest and release spores that infest seeds and soil.

Distribution.

Common bunt occurs presently worldwide. In Russia and countries of the former USSR T. caries is distributed in North-western Region, Non-Black Earth Zone, Lithuania, Byelorussia, western part of Ukraine, the Ural, North Kazakhstan, Siberia, and the Russian Far East. T. laevis is widespread in southern regions of Russia (Rostov, Astrakhan., Volgograd Regions, Krasnodar Territory), in the Transcaucasia, Middle Asia, Siberia, eastern part of Ukraine. The two species occur jointly in forest-steppe districts of Ukraine and Central Black-Soil Region. T. caries and T. laevis areas are sufficiently stable, and their repeated introductions in nontraditional zones have led to long-term development in these zones.

Ecology.

Maximum germination of teliospores in soil occurs at relative humidity from 40 to 60%, and the best penetration of infectious hyphae to seedlings occurs at soil temperature from 5 to 10.C. As a result, winter wheat sown late and spring wheat sown earlier than optimal times are strongly damaged.

Economic significance.

In nature the pathogen occurs on most wheat species and also on species of the genera Aegilops, Agropyron, Poa, Bromus, Secale. Common wheat is more damaged by smut fungi. Despite advances in control measures the disease continues to be a threat to wheat producers, especially in areas where seed dressing is not practiced. The disease reduces wheat yields and grain quality. Common bunt infection increases susceptibility of winter wheat plants to winter injury and other diseases. Infected plants produce grains of decreased weight, decreased length of stems and spikes, and slower developing root systems. Invisible losses caused by Common bunt (forming smut balls in place of kernels) are 5-6 times higher than direct ones, therefore protection measures are necessary. Chemical seed dressing and resistant varieties provide the best control of the disease.

Reference citations:

Karatygin I.V. 1986. Agents of cereal smut. Leningrad: Nauka. 112 pp. (In Russian)
Konovalova V.P., Chaika B.G. 1981. Damage of seed-growing wheat crops by Covered smut, depending on infection amount and reproduction conditions. Collection of papers: Reproductive process and crops yield. Odessa. 107-114 p. (In Russian)
Krivchenko V.I. 1984. Resistance of cereals to smut fungi. Moscow: Kolos. 304 pp. (In Russian)
Pronina M.M. 1982. Covered smut in Saratov region. Zashchita rastenii, 12: 46. (In Russian)
Sanin S.S., Nasarova L.N., Sokolova E.A., Ibragimov T.S. 1999. Health of cereals fields. Zashchita i karantin rastenii, 2: 28-31. (In Russian)
Varenitsa E.T., Mozgovoi A.F., Smirnitskaya P.P. 1977. Harmfulness of winter wheat head smut in the Non-Black Earth Zone and selection of resistant varieties. Vestnik sel.skokhozyaistvennoi nauki, 9: 30-32. (In Russian)

© Gultyaeva E.I.