Neotyphodium and Epichloë endophytes often influence beneficially on the host plant. Thus, could be used as a biological factor enhancing grass growth and resistance to stress factors. A detailed study was made to: (i) determine the infestation of genotypes of meadow fescue and red fescue, which occur in natural grass communities, in Poland by the Neotyphodium/Epichloë endophytes, (ii) define the level of ergovaline, a toxic alkaloid produced by active associations, (iii) determine the activity of antagonistic distinguishing isolates of endophytic fungi against selected microorganisms. There were analysed 204 genotypes of meadow fescue and 171 genotypes of red fescue. Mean frequency of the infection with endophytes was 74.5% and 64.3% respectively. Ergovaline was produced by 77% of E+ meadow fescue genotypes and 80.9% of red fescue genotypes. Mean content of the alkaloid was 0.202 and 0.151 µg·g DM^-1 respectively. FpII30, FpII67, FpII77, FpII168 and FrII82 demonstrated a high ability for protection of the host grasses from all the tested pathogens. These isolates due to high antimicrobial activity and a lack of ergovaline production have a great potential for biological control of grasses.

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