Diseases

Pythium aristosporum Vanterpool, Pythyium arrhenomanes Drechsl., Pythium graminicola Subram., Pythium ultimum Trow. - Pythium Root Rot of Wheat

Systematic position.

Class Oomycota, order Peronosporales, family Pythiaceae, genus Pythium.

Biological group.

Saprotroph.

Morphology and biology.

Fungi P.aristosporum, P.arrhenomanes, P.graminicola, P.ultimum attack root system of seedlings and young plants of wheat. The causal agents of the Root Rot have thin aseptate cobwebby colorless mycelium to 7mkm in diameter and chlamydospores. Their anamorph stage produces zoosporangia forming biflagellate zoospores. Teleomorph stage of the pathogens forms spherical oogonia with lengthened antheridia. As a result of sexual process, single, with a smooth membrane oospores arise. Light-brown spots appear on affected wheat roots. Dark-brown necroses (root rot) covered with colorless mycelium are formed on radical part of stalks. Sources of the infection are zoospores and oospores. The latter can be kept in soil to 10 years.

Distribution.

Pythium Root Rot of wheat is registered in the European Part of Non-Chernozem zone and at foothills of the Northern Caucasus of Russia, and in Estonia.

Ecology.

The causal agents of the Root Rot of wheat of the genus Pythium sp. are soil pathogenes. Their distribution and harmfulness grow sharply in conditions of the maximal soil humidification at temperature about 6oC.

Economic significance.

Fungi Pythium sp. inhibit growth or cause full destruction of seedlings and shoots. The actual yield losses of wheat caused by Pythium Root Rot were not studied. Control measures are crop rotation and presowing fungicide treatment of wheat seeds.

Related references:

Benken A.A., Korshunova A.F., Semenov A.Ya., Elbakyan M.A., Khatskevich L.K. 1977. Methodical recommendations on diagnostics of root rot of grain cereals. Leningrad: VIZR, p. 27-37 (in Russian).
D.yakov Yu.T. 1976. Family Pytiaceae. In: M.V.Gorlenko, ed. Fungi. Moscow: Пpocbeщehиe, p. 45-50 (in Russian).
Khokhraykov M.N., Dobrozrakova T.L., Stepanov K.M., Letova M.F. 1966. Keys to plant diseases. Leningrad: Kolos, 592 p. (in Russian).
Novotelnova N.S. & Pystina K.A. 1978. Root and radical rot of cultural plants. Leningrad: Nauka, 78 p. (in Russian).
Pidoplichko N.M. 1977. Fungal parasites of cultural plants. Guide, vol.1. Kiev: Naukova Dumka, 299 p. (in Russian).

© Yakutkin V.I.

The photos of morphological structures of the causal agent and of the affected plant belong to N.S.Novotelnova and K.A.Pystina, 1978 (p.14, 57). Fig.1. Morphological structures of the causal agent of the Root Rot of Wheat (Pythium sp.): a - mycelium, b - zoosporangium (unripe and germinating), c - oogonia with antheridia, d - oospore. Fig.2. Shoots of wheat affected by Pythium Root Rot.