Drechslera leaf spot in the common oat (Avena sativa L.) is caused by D. avenae (syn. Pyrenophora chaetomioides, Helminthosporium avenae). Susceptibility of various oat cultivars and breeding lines to leaf infection by this pathogen was investigated in the field in 2001–2002 and in a growth chamber. After natural infection in the field, brown or brown-red spots caused by D. avenae were found in all oat genotypes and both years, but were less common in the drier and colder growing season (2001). Mean values of leaf infection index in the studied oat genotypes for the 2 years varied from 5.65 (CHD 2100) to 10.33 (Akt). After artificial inoculation in the growth chamber, symptoms were similar but leaf infection index was much higher – from 15.0 (Bajka) to 41.3 (STH 4699). High-performance liquid chromatography showed that anthraquinone derivatives produced by strain 1 of D. avenae include anthraquinone compaunds – cynodontin and helminthosporin. These compounds are known to limit the growth of some other pathogens and saprophytes.

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