Diseases
Ustilago zeae (Beckm.) Ung. - Common Corn Smut
Systematic position.
Class Basidiomycetes, order Ustilaginales, family Ustilaginaceae, genus Ustilago.Synonym.
Ustilago maydis (DC.) Cda.Biological group.
Obligate parasite.Morphology and biology.
The fungus U. zeae causes the pathological growing of plant tissue, that is the formation of galls on all parts of corn plants. The first galls appear usually on root neck, later on leaves, stems, ears, and kernels. Mature galls can reach 30 cm in diameter. Teliospores are formed in galls. More than 370 millions of spores can be formed in 1 qub.cm of gall tissue. Teliospores are spherical, olive brown to black, 8-15 x 7-10 mkm. Teliospores grow and form dikariotic mycelium or sporidia. Mycelium infects plants, breaking differentiation of plant tissue and stimulating pathological growth of the tissue. The galls are formed during two weeks. Teliospores can infect plants during all vegetation period. In autumn at corn harvesting the galls break off, being able to winter on maize residues in field. In spring the teliospores infect corn again. The plants are more susceptible since panicle emergence till milk development stage.Distribution.
The disease is spread in practically all regions of maize cultivation. Two regions, the Caucasus and Moldova, are the original areas of infection spread in the former USSR. Here from the parasite has spread by seeds in Northern and Western districts of Ukraine, in Byelorussia and Russia. This disease has become widespread in 1950-60-s in connection with expansion of maize sowing throughout the country. The disease occurs more frequently in regions with lack of moisture. For example, it develops in steppe part of Ukraine stronger, than in Kuban region. In more humid regions of Central and Northern Russia the disease is spread everywhere, but the fraction of damaged plants is not high. In Siberia it is spread sparsely. In Moscow Region the number of infected plants reached 18-30% in 1955. In Leningrad Region only single plants were infected by the Common Corn Smut in 1960-s. The disease was rarely registered in Tatarstan and Bashkortostan, Pskov, Velikii Novgorod, Kaliningrad, Ryazan, Yaroslavl, Nizhnii Novgorod, Kirov, Chelyabinsk, Omsk, Novosibirsk Regions, in Northern districts of the Far East.Ecology.
Minimal temperature needed for teliospore growing is 0-5.C, optimal one is 20-30.C. The process of gall formation stops at temperature lowering to 20.C. Teliospores ripen better at high temperature. The spores can keep in soil during 3 years. Late sowing of maize is favorable for the disease development. The maize growing on the same field for 2-3 years increases the extent of infection by the Common Corn Smut from 10 to 18%. High moisture during maize vegetation limits the disease development. High temperature and lack of moisture favors its development.Economic significance.
This disease causes the strongest damage when ears and stems are infected. The losses of yield can reach 20-30%. In southern and south-eastern regions of Kazakhstan the yield losses can reach 53%. The yield reduction depends on the time of infection, on the place of infection on plants, on quantity of galls and their size. The yield losses can reach 48.7% when ears are infected. If the stems are infected below the ears, the yield decrease is about 25% only. Large galls decrease the yield by 60%, galls of average size by 25%, and small galls by 10%. Average decrease of productivity of infected by smut plants is about 30%. The maize infected by the Common Corn Smut is often more susceptible to stem blight. Control measures must be used: removal of residues from field, crop rotation, selection of healthy seeds, and treatment of seeds by fungicides.Related references:
Bzikov M.A., Misik N.A., Belaonova L.I. 1980. Role of precursors and fertilizers in decrease of yield losses from corn common smut. Kukuruza 6: 28 (in Russian).Chaika A.K., Martynyuk T.D. 2001. Damage of smut diseases to corn in Primorskii Territory. Kukuruza i sorgo 5:19-22 (in Russian).
Kalashnikov K.Ya., Shapiro I.D. 1962. Pests and diseases of corn. Leningrad: Selkhozgiz, 189 p. (in Russian).
Karatygin I.V. 1986. Agents of smut on cereals. Leningrad: Nauka, 112 p. (in Russian).
Nemlienko F.E. 1957. Diseases of maize. Moscow: Sel.khozgiz. 230 p. (in Russian).