Perennial ryegrass (Lolium perenne L.) is commonly infected with the endophytic fungus Acremonium lolii in a mutualistic relationship. The fungus produces a number of alkaloids, some of which are responsible for causing livestock disorders and/or for conferring insect resistance to the host grass. Little is known about the interrelationship between fungal growth and alkaloid production in the ryegrass plant and how this varies throughout the year. The concentrations fo A. lolii and two of its alkaloid metabolites, lolitrem B and peramine, were monitored in basal (mainly leaf sheath) and upper (mainly leaf blade) parts of 17 endophyte-infected ryegrass plants on a monthly basis for 1 year. A. lolii, lolitrem B, and peramine concentrations were lowest in winter. The highest A. lolii concentrations were recorded in early summer, which coincided with the development of plant reproductive structures. Lolitrem B concentrations were highest from summer to early autumn and were consistently highest in the basal part of the plant. Peramine concentrations were generally highest in the upper part of the plant. Individual plants contained different levels of A. lolii, lolitrem B and peramine. These differences were generally maintained throughout the year. Although data for each month were variable, regression analyses showed that yearly mean concentrations of lolitrem B and peramine in individual plants were closely related to, and therefore probably largely determined by, yearly mean concentrations of A. lolii.
