The relationship between mycotoxin synthesis and isolate morphology in fungal endophytes of Lolium perenne

•  Variability in the fungal endophytes of 83 natural populations of Lolium perenne (perennial ryegrass) from Europe was assessed. •  One plant per population was used for endophyte isolation and mycotoxin analysis. Variability in three isozymes, colony morphology and growth rate on potato dextrose agar (PDA), and synthesis of ergovaline, lolitrem B and peramine was recorded. •  Three species were found among 94 strains isolated: Neotyphodium lolii, Neotyphodium sp. (LpTG-2) and Gliocladium-like. The most frequent species was N. lolii, which showed high variability. In 12 populations, a single plant harboured two different endophytes. One-third of the isolates of N. lolii did not produce ergovaline whereas a few isolates did not produce lolitrem B. Ergovaline and lolitrem B-deficient strains, but not the few peramine-deficient isolates, had characteristic morphologies on PDA. No isolate was deficient for both ergovaline and lolitrem B synthesis. •  Selection of ergovaline and lolitrem-deficient strains based only on the morphology of the isolates in culture may be possible.