Diseases

Uromyces sojae Syd. - Rust of Soybean

Systematic position.

Class Basidiomycetes, order Uredinales, family Pucciniaceae, genus Uromyces.

Synonyms.

Phakopsora sojae (P. Henn.) Syd., P. pachyrhizi Syd.

Biological group.

This species is a biotroph.

Morphology and biology.

The Rust of Soybean most strongly develops in the second half of vegetation of plants. Small, rounded, rusty-brown, later dark-brown, powdery pustules are formed on leaves and project from epidermis. The affected leaves usually fall to the ground. Infecting agent is a monoecious parasite, passing all stages of development on soya. Spermatogonial and aecidial stages appear in the spring in an insignificant amount on the infected plants. Uredinial (the pustules are small, rounded, rusty-brown) and telial (the pustules are dark brown, almost black, mainly located on the lower side of leaves) stages develop later, being the most noxious. Urediniospores are unicellular, ovoid, light brown, 12 x 15-20 microns in size. Teliospores are unicellular, rounded, brown, having papillary apex, positioned on elongated peduncle, 20-25 microns in diameter. The fungus winters on infected vegetation residues as teliospores. In spring the teliospores germinate in basidium with basidiospores, which spread by wind to new plants.

Distribution.

USA, China, Japan, Korea, Congo, Sri Lanka, Ukraine. In the formet USSR the species is distributed in the Northern Caucasus and the Far East.

Ecology.

Rust development is promoted by frequent precipitation, plentiful dew, and air temperatures of 20-25.C. Dry and hot weather constrains disease development.

Economic significance.

The fungus parasitizes soya only. The harmful activity of the rust contributes to the disruption of physiological and biochemical processes in the plant; photosynthesis is especially reduced which results in the reduction of yield. Autumn plowing, early sowing, destruction of intermediate host, the use of early ripening varieties and fungicide treatments of plants reduce the disease development.

Reference citations:

Khokhraykov M.N., Dobrozrakova T.L., Stepanov K.M., Letova M.F. 2003. Keys to plant diseases. Saint Petersburg: Lan'. 592 p. (In Russian)
Peresypkin V.F. 1989. Agricultural phytopathology. Moscow: Agropromizdat. 480 p. (In Russian)
Transhel V.G. 1939. Review of rust fungi of the USSR. Moscow-Leningrad: Nauka. 426 p. (In Russian)

© Kungurtseva O.V.