Summer Dormancy and Survival of Tall Fescue in Relation to Endophyte Presence.

Summer dormancy is a known drought escape mechanism for Mediterranean-origin perennial grasses.  Little is known of the influence of fungal endophytes (Neotyphodium spp.) on the expression of summer dormancy in their grass hosts or of the possible role of endophytes in host drought survival.  Research was conducted to investigate interactions between summer dormancy potential and endophyte symbiosis as related to plant survival, and to determine relationships between biochemical protectants and drought survival in tall fescue (Lolium arundinaceum).  Field plots were established either under full irrigation or non-irrigation.  The experiment was a split-strip design with water treatments comprising main plots within each of which a 3 (cultivar) x 2 (endophyte status) factorial arranged in strips with four replicate blocks.  Plants of two populations (TX06V-B-FA and ‘Grasslands Flecha’) that have incomplete summer-dormancy and the summer-active cultivar ‘Kentucky-31’ (KY) were evaluated for shoot dry matter production, shoot senescence, tiller-base water content, dehydrin expression, superoxide dismutase (SOD) activity, and total free phenolic concentration.  Incompletely summer-dormant populations achieved 100% survival even in the absence of endophyte.  No benefit from endophyte symbiosis was found in any measurement of summer-dormant populations.  Summer-dormant populations exhibited lower biochemical-protectant expression, suggesting the dormancy trait caused decreased metabolic activity.  In general, KY had greater summer dehydrin expression, SOD activity, and total phenolic levels (except in late summer) than summer-dormant populations.  Summer-dormant populations exhibited less growth (P<0.001), lower tiller-base water content (P<0.001 to P<0.065), and greater senescence (P<0.008) than KY during the summer.  Preliminary results suggest that endophyte symbiosis does not affect survival of summer-dormant populations of tall fescue.  Low metabolic activity in summer-dormant populations may contribute to low biochemical-protectant expression and maintenance of tiller meristem viability and thus tiller survival and recovery.