An ascomycetous endophyte isolated from Mentha piperita L.: biological features and molecular studies.

A hyaline sterile fungus forming epiphyllous mycelial nets was isolated from meristem cultures of Mentha piperita. Histological studies indicated that the culture isolate is able to colonize stems and leaves with no damage to the host plant. In vitro-grown peppermint plants displayed enhanced vegetative growth when infected by the fungus, with mycelium extending from green tissues to growing rootlets. The production of very thin hyphae growing away from host meristems and the asymptomatic nature of the symbiosis were commonly observed in cultures, where the isolate never sporulated. No attribution to a precise morphospecies was therefore possible and the fungal culture was named sterile mycelium PGP-HSF. Through comparison of the 18 S rDNA sequence of the epibiont to those available in literature and in GenBank we were able to determine that the mutualist of peppermint is a member of the Pyrenomycetes, belonging to the subclass Sordariomycetidae.