ENDOPHYTE‐HOST ASSOCIATIONS IN FORAGE GRASSES. XV. CLUSTERING OF STROMATA‐BEARING INDIVIDUALS OF AGROSTIS HIEMALIS INFECTED BY EPICHLOË TYPHINA

Population studies involving the grass Agrostis hiemalis infected with the endophytic fungus Epichloe typhina were made. Grass individuals were assessed for infection state (presence or absence of fungus), number of culms and fungal stromata, and location within plot. Using clustering and ANOVA procedures available in SAS, geometric groups were identified and analyzed. The tendency of plants to bear stromata was found to be significant with respect to both the plot (P < 0.05) and the cluster (P < 0.0001) within which plants occurred. A cultural study was made of the endophytes from one of the plots. Here isolates from a cluster containing stroma-bearing grass individuals were found to grow more rapidly than those from grass clusters without stromata on a variety of sugars naturally available in vivo. Histological studies of the host demonstrate that the endophyte is seed transmitted in a comparable fashion to endophytes in other grasses. It is suggested that the clustering of stromata-bearing plants in Agrostis hiemalis is the result of the presence of aggressive strains of endophyte within proximally located plants.