Diseases

Ascochyta avenae (Petr.) Sprague et Johnson. - Ascochyta Leaf Spot of Oats

Systematic position.

Class Deuteromycota, order Sphaeropsidales, family Sphaeropsidaceae, genus Ascochyta (Ainsworth, 1971). Now this species is situated at Mitosporic fungi. Teleomorph - Didymella automnalis Petr. - class Ascomycotina, order Dothideales, family Dothideaceae.

Biological group.

Hemibiotroph.

Morphology and biology.

Ascochyta avenae infects mainly oats and very rarely, species of Hordeum, Triticum, and Lolium. Disease forms oblong, pale-orange spots with thin red-brown border. Subsequently the spots merge into the continuous white strips limited by leaf fibers. Pycnidium is spherical, 90-190 microns in diameter, formed on the lower leaf surface. Pycnidiospores (conidia) ellipsoid, pale yellow or colorless, with 1-2 partitions, 16-20 x 4-7 microns. During vegetation conidia are the main source of infection. At the end of vegetation the perithecia of the fungus sexual stage (Didymella autumnalis Petr.) are formed on the spots and also on the lower leaf surface. Asci are cylindrical, 30-60 x 10-16 microns. 8 colorless bicellular ascospores are situated in each ascus, being 9-16 x 4-5.5 microns in size. The fungus over-winters as perithecia; renewal of the infection occurs with ascospores in the spring.

Distribution.

It is found on all continents where oats are cultivated. In Russia it is found in all regions of oat cultivation. The disease is most severe in the Northwest region of Russia and in Byelorussia.

Ecology.

Damp warm weather is the best condition for the development of this disease.

Economic significance.

In favorable years moderate disease development may reach 20-30% which results in essential yield losses. Some varieties (Stendsky small early, Priekulskii belokolosyi) perish during the booting stage when disease pressure is strong. Control measures include: crop rotation, timely sowing, deep plowing, and foliar fungicide treatment.

Reference citations:

Ainsworth G.C., ed. 1971. Ainsworth and Bisby's Dictionary of the fungi. CAB International. 663 p.
Hawksworth D.L., Kirk P.M., ed. 1995. Ainsworth and Bisby's Dictionary of the fungi. CAB International. 616 p.
Ishkova Т.I., Berestetskaya L.I., Gasich E.L., Levitin M.M., Vlasov D.Yu. 2002. Diagnostics of the main fungus diseases of cereal crops. St. Petersburg: VIZR. 76 p. (In Russian)
Nikitina E.V., Polozova N.L. 1990. Diagnostics of cereal fungus spots. Leningrad: VIZR. 69 p. (In Russian)
Shestiperova Z.I., Polozova N.L. 1973. Powdery mildew dew and spots of summer grain crops. Leningrad: Kolos. 55 p. (In Russian)

© Dmitriev A.P.