A method of improving viability, persistence, and/or vigor of a host plant in the form of Lolium multiflorum Lolium x hybridum and Lolium perenne (host grass) includes artificially inoculating the host grass with an LpTG-1 endophyte RGT15 strain. The LpTG-1 endophyte RGT15 strain can produce at least one alkaloid or combination of alkaloids that provide the host grass with a favorable alkaloid profile and/or protect the plant from biotic stresses.