Ultrastructure ofAcremonium coenophialum,Acremonium lolii, andEpichloe typhinaendophytes in host and nonhostFestucaandLoliumspecies of grasses

摘要

Ultrastructural studies were made ofAcremoniumfungal endophytes of tall fescue and perennial ryegrass and two isolates ofEpichloe typhina. Hyphae of these fungi were observed in leaf sheaths of their natural host plant grown from infected seed and in artificially inoculated nonhostFestucaandLoliumspecies of grasses. Hyphae were also studied from fungal colonies grown on cellophane on potato dextrose agar. Crystalline inclusions were found in all endophytendash;host combinations with the exceptions ofE.typhinafrom perennial ryegrass in its own host and in a nonhost tall fescue, andAcremonium coenophialumin a nonhost perennial ryegrass. Tubular complexes were seen only inAcremonium loliiwhen growing in both host and in a non-host tall fescue. Three structures not seen before in endophytes (bundles of microtubules, 55 to 60ensp;nm diameter "tubes," and bilayered cell walls) were found inE.typhinagrowing only in perennial ryegrass, its natural host. None of the distinguishing ultrastructural components described were found in hyphae grown in culture. Our observations suggest that endophytes express specific ultrastructural features only when they are grown in the grasses. However, it was not readily discernible what function the components serve and what role, if any, the natural versus the nonhost grass plays in the expression of endophyte ultrastructure.