Diseases

Pyrenophora avenae Ito et Kurib. - Helminthosporium leaf spot of oats.

Systematic position.

Class Ascomycetes, Order Spheriales, Family Pyrenomycetes, Species Pyrenophora avenae Ito et Kurib. (Ainsworth, 1971).

Biological group.

Hemibiotroph.

Morphology and biology.

Helminthosporium (red-brown) leaf spot is caused by the fungus Drechslera avenae (Eidam) Scharif. (= Helminthosporium avenae Eidam) - asexual stage of Pyrenophora avenae. It is a common disease of oats and may occasionally attack species of Hordeum, Koeleria and Arrhenatherium. Sexual stage Pyrenophora avenae Ito et Kurib. form in the spring on crop debris (Nikitina & Polozova, 1990). Disease attacks leaves and kernels of oats. Oblong to elongate, reddish-brown spots may appear on seedling leaves soon after emergence. Spots on stems may be long and narrow or broad and irregular in shape. At start spots are little, white in the center, bordered by red brown zone, 1-3 x 1-2 mm. Later spots are elliptic, gray or brown in the center with red-brown border and brown zone, 20-40 x 5-10 mm. The outer borders of the spots are poorly defined, brown color merging into yellow or reddish shades. Spots frequently spread over most of the infected leaf. Oat heads may also become infected (Ishkova et al., 2002). The fungus enters the hulls surrounding the kernels and may even penetrate the kernels slightly. Diseased kernels turn brown at the basal stem. The fungus survives as spores or mycelium on plant debris and as spores on the seed, or as mycelium beneath the seed coat. The fungus spreads as spores from plant debris. Infection on plant parts is commonly associated with splashes of rain drops. Spores are often lodged in the hulls of the grain, providing a source for infection. Spores produced on the spot are dispersed by various means to other leaves of the same plant or to other plants. Spores (conidias) normally are single, straight, cylindrical, rarely inversely-clavat, pale-brown to olive-brown, with 1-9 partitions 50-130 x 15-20 . (Ishkova et al., 2002).

Distribution.

In different countries where oats are cultivated in Europe, Asia, Africa, America and Australia. In Russia present in the entire region where oats are cultivated (Ishkova et al., 2002).

Ecology.

The fungus is the common causes of seedling blights of oats in different climatic zones. Some factors, such as freezing, herbicide injury, nutrient deficiency, or infection by other pathogens may result in the disease development. Rains and moist, humid periods favor disease infestation because spores germinate at temperatures of 10-20 degrees centigrade and 100% humidity (Motovilin, 2000).

Economic value.

Because of the destruction of leaf tissue, photosynthesis is reduced in diseased plants, resulting in light or shriveled grains; direct attack of kernels by the fungus also results in light or shriveled kernels. Severe disease attacks have caused yield losses as high as 30-40 percent (Motovilin & Strigekozin, 2000). Control measures: crop rotation, burying plant debris, application of seed-treatment and foliar fungicides (Motovilin, 2000).

Reference citations.

Ainsworth G.C., ed. 1971. Ainsworth and Bisby.s Dictionary of the Fungi. CAB International. 660 p.
Ishkova T.I., Berestetskaya L.I., Gasich E.L., Levitin M.M., Vlasov L.Iu. 2002. Diagnostics of the main fungus diseases of cereal crops. Saint Petersburg: VIZR. 76 p. (In Russian)
Motovilin A.N. 2000. Responsiveness of oats varieties on fungicides application against red-brown spot. Protection and quarantine of plants, 10: 30. (In Russian)
Motovilin A.N., Strigekozin Ju.A. 2000. Estimation of oats basic disease harmfulness. Protection and quarantine of plants, 7: 28. (In Russian)
Nikitina E.V., Polozova N.L. 1990. Diagnostic of cereal fungus spots. Leningrad: VIZR. 69 p. (In Russian)