Grasses are very often infected by endophytic fungi of the Neotyphodium and Epichloë genera. They can produce metabolites toxic to livestock as well as beneficially affect grasses. Thus, endophytes can be used for plants improvement. These facts stimulated a more detailed investigation aimed at providing more insight into the problem of these endophytes in Poland. The aims of the research were as follows: (i) to determine the levels of colonization of Polish-grown cultivars of perennial ryegrass, meadow fescue, and red fescue with endophytic fungi of the genera Neotyphodium and Epichloë; (ii) to determine the potential hazards associated with the toxins produced by the active associations; (iii) to isolate viable endophytes of the genera Neotyphodium and Epichloë from active associations; and (iv) to determine the levels of antagonistic activity of the obtained endophyte isolates against selected microorganisms, in particular serious grass pathogens, in vitro. The staining method was used for endophytes detection in grass seed collection. Endophytes were isolated on PDA medium and characterized. Antagonistic activity of N/E isolates and seed extracts were determined in dual culture assays and on microscope slides respectively. Ergovaline and lolitrem B content were assayed. There were 242 samples of seeds of 50 cultivars of grasses collected in Poland, including 124 samples of 20 cultivars of perennial ryegrass, 61 samples of 10 cultivars of meadow fescue, and 57 samples of 20 cultivars of red fescue. Endophytic fungi were only detected in 33 seed samples of 5 perennial ryegrass cultivars and in 15 samples of 2 meadow fescue cultivars. The levels of seed colonization of these species reached maximum 8 and 90%, respectively. No colonization by endophytes was found in seeds of red fescue. The viability of endophytic mycelium in the seeds of perennial ryegrass and meadow fescue was very low. Endophytic fungi were isolated only from 3 and 4 samples of these grasses respectively. In laboratory conditions, endophytic fungi showed stronger antagonistic properties at 25°C. The highest and most frequent growth inhibition was observed for M. nivale, Rhizoctonia solani, Fusarium avenaceum and F. equiseti. The obligate pathogens B. graminis, P. coronata, and P. graminis ssp. graminicola were not sensitive to water and alcohol extracts of E+ seeds. Isolates Fp28, Fp40, and, to a lesser degree, Fp37, originating from meadow fescue, were characterized by the strongest antagonistic properties. Moreover, they did not produce (Fp28 and Fp37), or produced only small amounts (Fp40) of, ergovaline, which is toxic to animals. After additional tests, they could be used as biological factors for improving the utility value of new grass varieties and their resistance to stress factors.

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