Ustilago nuda (Jens.) Kellerm. et Swingle Loose Smut
Synonyms.Ustilago nuda (Jens.) Rostr., Ustilago segetum (Pers.) Roussel var. hordei Rostr. et Jens, f. nuda Jens.).
Systematic position.Class Basidiomycetes, order Ustilaginales, family Ustilaginaceae, genus Ustilago.
Biological group.Obligate parasite, attacks cultivated barley and species of the genus Hordeum.
Morphology and biology.Loose Smut symptoms are obvious between heading and maturity. Barley heads are black to dark brown. Some diseased heads may be taller than any of their healthy neighbors. Most affected heads emerge slightly earlier than the normal ones, and their spikelets may be entirely transformed into a dry, olive brown spore mass. The thin membrane ruptures shortly after the heads emerge, and spores are dispersed by wind. Within a few days only the rachis remains, although awns may remain on heads. Infected seeds are fully germinable and not visibly altered. U. nuda fungus produces a hyaline, dikariotic mycelium in host tissue. At maturity, the hyphae of the mycelium thicken and fragment into teliospores, which are olive brown, globose to ovoid, spiny, and 3.6-9 microns (most often 5.5-6 microns) in diameter. The teliospore germinates to form a basidium. Compatible basidial cells or short hyphae produced by the former fuse to form infectious dikaryotic mycelium. U. nuda over-winters as dormant mycelium only within the embryo of infected barley seeds. When infected seeds germinate, the fungus is carried along with the growing point and ramifies in the shoot apex, culm nodes, and seed primordia. Usually all head tissues except rachis are invaded and converted into sori covered with delicate pericarp membrane. During the formation of the sori the hyphae differentiate and fragment into teliospores. The sorus membrane breaks down shortly after the heads emerge and frees the teliospores for dispersal. They land in open flowers and cause infection by growing through the ovary wall. The dikaryotic infection hyphae proceed between and through the cells to the developing embryo and become established in the tissue of the scutellum, embryo axis, and growing point. Teliospores are dispersed by wind. Although long-distance spread is possible, most infections probably occur only during flowering.
Distribution.Disease is widely distributed throughout the world. In CIS countries it is found everywhere in places where barley is cultivated.
Ecology.Disease favors wet, cloudy weather and moderate temperatures (16-22 degrees Celsius). These conditions promote longer and more open flowering for the host. A single heavy rain during flowering in affected fields can cause a 10-fold increase in infection.
Economic significance.The U. nuda is most significant in Eastern and Western Siberia, the Northern Caucasus, North-West and Central Regions of Non-Chernozem Region, South Ural, the Far East, also in Baltic region (Latvia, Lithuania), Belarus, Ukraine, Kazakhstan. The yield loss depends on disease development; with the frequency of disease occurrence at 0.7-4.7% the losses can reach 22.3-31.6%. In Ukraine the yield losses are estimated at 14%. Local epiphytoties can take place in any agroclimatic zone with the infringement of agronomical norms (e.g., untreated seeds). Therefore, it is impossible to designate an epiphytotic zone.
Reference citations:Buidvis K.R., Kokha M.I. 1975. Studies of race composition of causal agent of Loose Smut Ustilago nuda (Jens.) Rostr. in barley fields in Latvian SSR. Izvestiya akademii nauk Latviiskoi SSR, 1: 25-29. (In Russian)
Chumakov A.E. 1962. Forecasting distribution of main diseases of field cultures for 1962. Plant Protection against pests and diseases, 3: 47-49. (In Russian)
Ishkova T.I., Berestetskaya L.I., Gasich E.L., Levitin M.M., Vlasov D.Yu. 2000. Diagnostic of the main diseases of cereals. Saint Petersburg: VIZR. 76 p. (In Russian)
Kirdoglo E.K., Shevchenko E.P. 1986. Level of harmfulness of Barley Loose Smut in Forest-steppe zone of Ukraine. Scientific-technical proceedings of All-Union Breeding and Genetic Institute. Odessa: VSEGEI. 59-61 pp. (In Russian)
Kozhevnikova L.M. 1970. Species of Barley Loose Smut in Voronezh Region. Plant Protection against pests and diseases, 2: 19-20. (In Russian)
Mathre D.E., ed. 1997. Compendium of barley diseases. St. Paul, Minnesota: APS PRESS. 90 p.
Novozhilov K.V., Zakharenko V.A., eds. 2000. Levels and tendencies of variability of species composition and intra-population structure, areas of complexes of harmful and useful organisms and forecast of dangerous phytosanitary situations in zones of the country. St. Petersburg: VIZR. 100 p. (In Russian)
Oniskova M.G. 1989. Distribution and specialization of races of causal agent of barley loose smut in the North Kazakhstan. Proceedings "Theoretical bases of agricultural culture breeding in North Kazakhstan". Tselinograd. 74-76 pp. (In Russian)
Sanin S.S. 1995. Phytosanitary monitoring: modern state and ways of improvement. Problems of Optimization of Phytosanitary State in Plant Industry. Proceeding of All-Russian Meeting on Plant Protection. St. Petersburg: VIZR. 166-175 pp. (In Russian)
Stepanovskikh A.S. 1970. Studies of species structure of Barley Loose Smut in virgin region, Kurgan and Chelyabinsk Regions. Plant Protection of Agricultural Cultures Against Pests and Diseases. Kurgan: KSKhI. 17-26 pp. (In Russian)
Tikhomirov V.T., Sidorova E.F. 1991. Resistance of spring barley to Loose Smut in Eastern Siberia and ways of it's improving. Siberian Vestnik of Agricultural Science, 5: 55-58. (In Russian)
Tyunin V.A., Kushnirenko I.U. 1981. Species structure and distribution of causal agents of Barley loose Smut in Chelyabinsk Region. Regional Systems of Plant Protection Against Pests and Diseases in Siberia. Novosibirsk. 29-31 pp. (In Russian)