Neotyphodium fungal endophyte in tall fescue (Schedonorus phoenix): a comparison of three Northern European wild populations and the cultivar Kentuky-31

Pooideae grasses may be colonized by systemic fungal endophytes. The fitness of endophyte depends entirely on resources and seed transmission from the host plant, while colonized plants may gain increased survival, growth, and reproduction relative to their uncolonized conspecifics. Most research of endophyte-grass interactions have been carried out on few cultivars of tall fescue (Schedonorus phoenix) and their symbiont Neotyphodium coenophialum. Lack of studies using wild populations of tall fescue across the species natural distribution range, however, limits the understanding of the ecological and evolutionary role of the symbiosis in nature. We performed a common garden experiment in Southern Finland with three wild, tall fescue populations from northern Europe and the forage cultivar Kentucky-31 (KY-31). For each population, we used naturally endophyte-colonized, naturally endophyte-colonized but endophyte removed (decolonized), and naturally uncolonized plants to separate effects due to the host genotype from the endophyte. We evaluated growth variables and survival in four environmental treatments of varying water and nutrients. Supply of water and nutrients increased plant biomass and reproductive effort in all populations. This effect was higher for KY-31 plants which produced on average 55 % more seeds than wild plants, indicating better adaptation to high resource environments. However, the higher incidence of Claviceps sp. and the low winter survival indicated KY-31 tall fescue is mal-adapted to Northern European conditions. Naturally colonized plants had greater plant biomass (a parts per thousand 12 %), reproductive effort (a parts per thousand 22 %) and seed mass (a parts per thousand 29 %) than naturally uncolonized and decolonized plants. Nonetheless, endophyte colonization did not affect plant survival, and the effects of endophyte colonization on tiller number, panicle/tiller ratio and Claviceps sp. incidence depended on the population origin. In the wild populations, endophyte removal only reduced the number of tillers (a parts per thousand 29 % lower), while the difference between naturally colonized and naturally uncolonized plants was not significant. Our results show that endophyte symbiont increases tall fescue performance in general, but the differences between wild populations and cultivars indicate adaptation to local habitats and agronomic management, respectively. The comparison of naturally endophyte-colonized and decolonized plants suggests certain plant genotype-endophyte combinations found within populations result from local selection pressures.