Plants can be affected by micro-organisms of several types including bacteria, viruses and fungi. Most have what scientists refer to as “perfect” reproduction, i.e., spores are released into the air and can then move to other locations and other plants, resulting in infection at new locations.
However, with endophytic (internal) fungi, which can occur in tall fescue and perennial ryegrass, there is no perfect stage. This type of fungus is transmitted only through seed; it does not move in air or water, is not harbored in the soil and does not move from plant to plant in any known natural way.
Regardless of whether a plant is endophyte-free or infected with either a toxic or a non-toxic endophyte, its endophyte status will remain unchanged in nature. 
From Forage-Livestock Quotes and Concepts, D.M. Ball, et. al
