Host specificity and compatibility studies have been conducted using seedling inoculation techniques. Neotyphodium and Epichloë can form novel associations with grasses closely related to their natural host species (Christensen, 1995; Chung et al., 1997; Leuchtmann and Clay, 1993; Siegel et al., 1990). Some associations may be fully compatible and stable. Others result in cellular incompatibility, premature death of hyphae, or death of host tissue resembling a host-specific hypersensitive response (Fig. 14-33 and 14-34) (Christensen, 1995; Koga et al., 1993). Some novel associations stunt the growth of the host (Fig. 14-35), but do not result in obvious cellular incompatibility reactions (Christensen et al., 1997). It is not understood why attempts to form associations between Neotyphodium and grasses not closely related to their natural host grass are unsuccessful.


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Fig. 14-33. Incompatibility in a tall fescue plant inoculated with a Neotyphodium endophyte from perennial ryegrass resulting in dead tissue (-->) in the shoot apex region.


Fig. 14-34. Naturally infected compatible interaction of tall fescue with Neotyphodium coenophialum.




Fig. 14-35. Growth of tall fescue plants inoculated with different single ascospore strains of Epichloë festucae. The left two plants were inoculated with one strain and the two plants at right with another strain. No cellular incompatibility reactions were detected in the stunted plants during examination involving light microscopy and transmission electron microscopy.



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