FUNGAL AND HOST GENOTYPE EFFECTS ON COMPATIBILITY AND VASCULAR COLONIZATION BY EPICHLOE-FESTUCAE

Parental and progeny isolates of the endophytic fungus Epichloe festuc ae were tested for compatibility with five grass species: Lolium peren ne, Festuca arundinacea, F. longifolia, F. pratensis, and F. rubra sub sp. rubra. One parental and some progeny isolates adversely affected t he growth of plants, causing increased mortality of inoculated seedlin gs, stunted growth and chlorotic leaf symptoms. Growth of hyphae from surface-sterilized leaf sheaths and blades was more vigorous and conce ntrated from stunted than from symptomless plants. In addition, the gr owth of isolates was influenced by the host species, whereby estimates of hyphal concentration were consistently highest in meadow fescue as sociations and lowest in tall fescue associations. Light microscopic a nd transmission electron microscopic examination of stunted plants ind icated no changes in host cells. Intercellular hyphae were observed wi thin vascular bundles of leaf blades and sheaths of many of the endoph yte-grass associations. The frequency of infected vascular bundles and the concentration of hyphae within them was highest in plants infecte d with the stunting parental isolate and lowest in plants infected wit h the symptomless parental isolate. Hyphae within vascular bundles wer e typically in close contact with sieve-tube elements and appeared to be functioning as powerful sinks, diverting assimilates and restrictin g growth.