INCOMPATIBILITY OF SOME GRASS-ACREMONIUM ENDOPHYTE ASSOCIATIONS

During a long-term project to create novel Acremonium-grass associatio ns through inoculation of seedlings it was noted that the leaf sheaths of Lolium perenne plants inoculated with some isolates of A. coenophi alum contained distorted hyphae lacking in cytoplasmic inclusions. Hos t-endophyte interactions within leaf sheaths were examined using some of these plants, together with natural L. perenne. A. lolii associatio ns, and some novel L. perenne-Acremonium associations in which the hyp hae appeared normal. Vital staining and attempts to isolate fungi from leaf sheaths of varying ages revealed that most hyphae in the second and third leaf sheaths of the L. perenne-A. coenophialum associations were dead. Transmission electron microscopy showed that the hyphae had become distorted and collapsed, with degenerated cytoplasm and cell w alls which were electron dense and lacked a fibrous outer layer found in most other Acremonium-grass associations. No hypersensitive reactio ns were observed within the host cells surrounding the degenerated hyp hae. However, the intercellular matrix which maintained contact betwee n host cell walls and hyphae had become electron dense. The changes to the intercellular matrix may be accompanied by a decrease in permeabi lity and nutritional value, or both, of the matrix which could have ca used the apparent incompatibility observed in this study.