The fungal endophytes: does the rate of mycelium growth decrease with host age and host generations?

Vertical transmission of endophytic fungi is imperfect. Fungal endophytes do not always enter seeds of the host on which they live. One of the factors affecting the effectiveness of vertical transmission may be the fungal growth rate. We have hypothesized that the rate of mycelium growth of the endophytic fungus Epichloë poae decreases with host plant age and in successive years of the host and fungal generations. The hypothesis was tested in vitro, by using passaging of fungal mycelium to imitate vertical transmission in plants. Growth rate of the fungus decreased with host plant age and in successive in vitro passages. Fungal growth rate differed between Epichloë isolates from the first and second generations of the grass. We treated fungal growth rate as a potential indicator of fungal performance that may be associated with the ability of the endophyte to reach and colonize developing seeds.