Diseases

Gaeumannomyces graminis (Sacc). Arx et D.L. Olivier - Root Rot.

Taxonomic position.

Section Ascomycota, family Magnaporthaceae, genus Gaeumannomyces.

Synonym:

Ophiobolus graminis (Sacc). Sacc. Anamorpha: Phialophora radicicola Cain.

Biological group.

Disease of cereal roots.

Morphology and biology.

The disease appears during phase of sprouts. Roots, stalk bases and sheaths are attacked. The roots darken and rot, destroyed at knot of tillering. The sprouts die with strong severity of the disease. At the stalk base (first and second internodes) necrotic dark brown spots are formed, covered with black velvety fungal scurf. The plants lag in growth and turn yellow; leaves and sometimes the entire plant die. The mycelium and large amount of perithecia are accumulated under vagina of lower leaf. As a result of an atrophy of productive stalks, of nanism and white stems, light patches are formed on crop fields during stage of earring. The primary infection of plants takes place by ascospores. The ascospore release coincides with start of sowing of winter crops that may cause infection of shoots from autumn. Transfer of the infection from plant to plant happens with contact of diseased and healthy roots in soil. Mycelium septate; immersed mycelium pale brown or brown; air one pale grey. Ascoma (perithecia) black, smooth, single or gregarious, forming on a stalk under a wrapper of the lower leaf; immersed from the beginning, later (upon maturing) projecting; 300-500 microns in diameter, with arched neck, frequently reaching length of perithecium. Ascus unitunicate, oblong-clavate, straight or arched, with short peduncle or sedentary, rounded at apex, with thin wall, 80-115 x 9-13 microns, 8-sporous. Ascospores in bundles, filamentous, occasionally arched, wider in the middle, gradually narrowing to apices; young ones single-celled, upon maturing having 3-7 septa, almost colorless, generally yellowish. Conidiophores lengthy, brown, smooth, septate, raising from air hyphae of mycelium; single-celled or multicellular, simple or dichotomously branched. Frequently hypha has phialides at apex. Phialides single or in groups of two or three, hyaline or light brown, wider at base and narrowing at tip, straight or arched, with noticeable collar. Phialides generate spores endogenously; the spores are single-celled, hyaline, sickle-shaped, arched, 5-9 x 0.7-1.7 microns. Some strains form microsclerotia and chlamydospores. Microsclerotia numerous, black, spherical, about 1 mm in diameter. The fungus is maintained on debris from year to year in form of mycelium, perithecia, sclerotia, and chlamydospores.

Distribution.

Europe, Asia, Africa, America, Australia. In Russia it occurs more often in districts with sufficient humidity. Most harmful in northwest and central districts of Non-Chernozem region, in some areas of Central Chernozem region, in the Northern Caucasus. In CIS a zone of the greatest harm embraces western districts of Lithuania; Latvia, Estonia, Byelorussia; western and southern districts of Ukraine; majority of Moldova.

Ecology.

Intensive propagation of fungus occurs at temperatures ranging from 18-28. C; suppressed at 30. C and higher. The severity increases at moderate and weak soil acidity levels (pH 5-6.5). At neutral and low alkaline reaction (pH 7.5) growth lags. Optimal humidity is 50-80%. High air temperatures in autumn, abundant autumn dews, and increased soil humidity promote strong development of the disease, creating favorable conditions for maturing and rapid germination of spores and winter wheat infection. The fungus develops on mild, well-aerated soils having poor organics. In spring, disease distribution is promoted by high relative air humidity, increased soil dampness, and rather low temperatures.

Economic significance.

The disease belongs to group of dangerous diseases of wheat and barley in many countries of Europe, America, and also Australia. In the former USSR yield losses reach, in epiphytotic years for example, about 20% in the Northern Caucasus and 3.1-6.8% in Byelorussia. Protective measures include cultivation of resistant cultivars; control of weeds of the family Poaceae reserving the infection; removing vegetative debris; using correct rotation (good precursors are fallow lands, leguminous cultures, potatoes); application of organic and mineral soil fertilizers based on zonal references, with addition of nitrogen fertilizers during early spring; grain-treatment by fungicides.

Reference citations:

Endeladze N.E. 1970. Results of study of biology Ophiobolus graminis Sacc. - causal agent of wheat root rot and its control. - Kornevye gnili khlebnykh zlakov i mery bor.by s nimi, P. 71-75 (in Russian).
Endeladze N.J. 1975. Root rot of wheat and barley in Georgia// Tezisy dokladov soveshchaniya "Kornevye gnili sel.skokhozyaistvennykh kul.tur", Tbilisi, P. 67-69 (in Russian).
Golubnitseva A.P., Saveljeva N.I. 1975. Root rot of cereals in the Pskov Region// Tezisy dokladov soveshchaniya "Kornevye gnili sel.skokhozyaistvennykh kul.tur", Tbilisi, P. 7-8 (in Russian).
Ibragimov G.R. 1984. Mycoflora of wheat root rot in Azerbaijan// Tezisy dokladov VII Konferentsii po sporovym rasteniyam Srednei Azii i Kazakhstana, 11-14 Sept. 1984, Alma-Ata, P.215-216 (in Russian).
Korshunova A.F. 1970. Root rots of winter wheat and winter barley near the North Caucasus. - Kornevye gnili khlebnykh zlakov i mery bor.by s nimi, P. 46-49 (in Russian).
Korshunova A.F. 1975. The basis of wheat protection against ophiobolesis // Tezisy dokladov soveshchaniya "Kornevye gnili sel.skokhozyaistvennykh kul.tur", Tbilisi, P. 40-41 (in Russian).
Korshunova A.F., Chumakov A.E., Shekochikhina R.I. 1976. Control of wheat root rots. Leningrad: Kolos, 184 p. (in Russian).
Kuznetsova M.A., Ivanchenko M. J. 1970. The influence of predictors on winter wheat root rot in steppe region of Kabardino-Balkaria. - Kornevye gnili khlebnykh zlakov i mery bor.by s nimi, 1970, P. 64-66 (in Russian).
Ponomareva G.J. 1970. The formation of spores of causal agent of winter wheat root rot Ophiobolus graminis Sacc. - Kornevye gnili khlebnykh zlakov i mery bor.by s nimi, P. 122-124 (in Russian).
Shirko V.N. 1948. Root rot of cereals in wet regions of the USSR// Trudy VIZR, 1, Moscow - Leningrad: OGIZ-SELKHOZGIZ, P.47-50 (in Russian).
Shirko V.N. 1953. Winter wheat root rot, caused by Ophiobolus graminis Sacc.// Sbornik rabot Inst. prikl. zoologii i fitopatologii, Moscow - Leningrad, P.67-74 (in Russian).
Shkipsna J.E. 1970. Root rot (Ophiobolus graminis Sacc.) and its control on winter wheat in western Latvia. - Kornevye gnili khlebnykh zlakov i mery bor.by s nimi, P. 89-93 (in Russian).
Shpokauskene O.Ju. 1976. Winter wheat root rot and its causal agents in Litva// Tezisy dokladov nauchn.-prakt. konf. "Puti vnedreniya progressivnykh metodov zashchity rastenii v sel.skokhozyaistvennoe proizvodstvo", 28-30 Jun. 1976. Riga, P. 45-46 (in Russian).
Tupenevich S.M., Kononova G.A., Airumov L.P. 1977. Winter wheat Root rot in Non-Chernozem region, caused by Ophiobolus graminis Sacc.// Trudy VIZR "Kornevye gnili zernovykh kul.tur", Leningrad, P.36-40 (in Russian).
Volchkova U.M. 1970. Root rot of wheat in North Osetia. - Kornevye gnili khlebnykh zlakov i mery bor.by s nimi, P. 60-63 (in Russian).

© Ishkova T.I.