There are also reports of plant diseases not being affected by endophytes. Endophyte infected tall fescue seedlings were not protected from infection by Cochliobolus sativus (Ito & Kuribayashi) Drechs. ex Dastur (Trevathan, 1996) or from the turfgrass pathogens Magnaporthe poae Landsch. & N. Jacks and Pythium aphanidermatum (Edson) Fitzp. (Blank and Gwinn, 1992). The presence of endophyte in tall fescue or perennial ryegrass plants did not appear to influence the onset or severity of basal tiller rotting caused by Fusarium oxysporum (Schlect) Snyd. & Hans., F. equesite (Corda) Sacc., and Pythium acanthicum Drechsler in a greenhouse trial conducted by Hume et al. (1997).
There have even been instances where some strains of Neotyphodium endophytes were associated with increased susceptibility to disease. This was observed in turfgrass trials at Rutgers University by Funk et al. (1994), where turfgrasses infected with endophytes were more susceptible to Pythium blight than E- plants. They surmised that this could be an indirect effect of the endophytes promoting a denser, more lush turf that enhanced disease development. Krauss et al. (2007) and Phillips (personal communication, 2007) reported that ergot (Claviceps purpurea) was more severe on E+ tall fescue and perennial ryegrass than on E- plants. The mechanism for this is not known, but perhaps the florets of the E+ plants remain open longer and are thus more susceptible to infection from ergot ascospores.
Schmidt (1994) stated that seedlings of meadow fescue infected with the endophyte N. uncinatum (Gams, Petrini & Schmidt) Glenn, Bacon, Price & Hanlin had better survival than E- plants when attacked by Drechslera sorokiniana and Rhizoctonia cerealis, but poorer survival when attacked by Fusarium culmorum (Wm. G. Sm.) Sacc. Endophyte infected seedlings were slower to develop than E- seedlings, and this may have provided a better opportunity for infection by F. culmorum.