Endophytic Fungus Negatively Affects Salt Tolerance of Tall Fescue

Vertically transmitted endophytic fungi can mitigate the negative effects of salinity encountered by their host grass and alter the competitive interactions between plant individuals. To experimentally study the interactive effects of the fungal endophyte Epichloe coenophiala on salt tolerance and intraspecific competition of its host plant, tall fescue Festuca arundinacea, we subjected 15 maternal lines of each Epichloe associated (E+) and Epichloe free (E-) tall fescue to salt treatment and competition in the greenhouse and common garden. Then, to explore variation in endophyte incidence in natural populations of tall fescue, we surveyed 23 natural populations occurring on or near the Baltic Sea coast in Aland islands in southwestern Finland for endophyte incidence, distance to shore, and competitive environment. Under salinity in the greenhouse, E- plants grew larger than E+ plants, but there was no size difference in the control treatment. E- plants grew taller and were more likely to flower than E+ plants when grown in benign conditions in the common garden but not with salinity or competition. The frequency of Epichloe incidence was high (90%) in natural populations, and it decreased towards the shore and risk of salt exposure. These results demonstrate a negative effect of Epichloe endophyte on the salt tolerance of its host. The high incidence of Epichloe in natural populations of tall fescue in the northern part of the species distribution range is likely due to factors other than salinity.

Automated summary

Vertically transmitted endophytic fungi can mitigate salinity effects on host grass and alter competitive interactions. Experimentally, tall fescue plants without endophytic fungi grew larger under salt treatment, but there was no difference in control treatment. In the common garden, plants without endophytic fungi grew taller and were more likely to flower, but no difference was observed under salinity or competition conditions.