EFFECT OF AGAR MEDIA COMPOSITION ON GROWTH, CHROMATOGRAPHY PROFILES AND BIOLOGICAL ACTIVITY OF EXTRACTS OF PYRENOPHORA TRITICI-REPENTIS
The study was devoted to find out virulence factors of isolates of Pyrenophora tritici-repentis that do not produce Ptr ToxA toxin but are able to cause necrotic lesions on susceptible wheat varieties. The main task of the research was determination of the effect of agar media composition on linear growth, morphology, chromatogtraphic profiles and biological activity of extracts of ten ToxA+ and ToxA<sup>-</sup> isolates from north-west and south populations of the fungus. Origin of fungal isolates had much less effect on fungal growth, morphology and chromatography profiles of extracts than agar medium composition. Extracts of three (1 southern and 2 north-western ones) from ten isolates demonstrated phytotoxic activity. Analysis of UV spectra of major compounds detected in the extracts allowed finding y-lactams (on YES medium), anthraquinones (on YES, V8-KrA and V4 media), and unknown for P. tritici-repentis compounds. One of the novel substances from this fungus was purified and identified as 10,11-dehydrocurvularin, a well-known phytotoxic macrolactone possessing a wide spectrum of biological activity and antioxidant properties. However, this toxin was low active against leaves of couch grass and wheat while leaves of perennial sow thistle were highly sensitive. Possibly, dehydrocurvularin plays the secondary and protective role in the development of tan spot disease in wheat. Because it was found in both nec+ ToxA+ and nec+ ToxA<sup>-</sup> isolates of the fungus, it is necessary to further search for virulent factors of latter ones.