Improvement of salinity stress tolerance in tall fescue (Festuca arundinacea Schreb.) under the influence of symbiotic endophytic fungi

Background and Objectives: Tall fescue (Festuca arundinacea) is one of the most important grass species, widely used for forage production, soil conservation, and turf construction. It forms a symbiotic relationship with endophytic fungi of the genus Epichloë (Neotyphodium = Acremonium), which enhance the host plant's tolerance to biotic and abiotic stresses. This study aimed to investigate the role of symbiotic endophytic fungi in improving tall fescue tolerance to salt stress under hydroponic conditions.
Materials and Methods: To evaluate the effect of endophytic fungi on salt stress tolerance, endophyte-infected plants were first identified using rose bengal staining and propagated by tiller division. Half of the tillers were treated with fungicides (propiconazole and Folikor) to generate endophyte-free controls. Both endophyte-infected and endophyte-free clones were transferred to hydroponic culture containing Johnson's nutrient solution at half strength. After establishment, salinity treatments were applied gradually in three stages to avoid osmotic shock. A factorial experiment based on a completely randomized design with three replications was conducted, with factor A being the presence or absence of endophytic fungi and factor B being salinity stress at four levels (control, 0.5%, 1%, and 1.5% NaCl). One month after salt treatments, data were collected on tiller number, leaf length, shoot fresh and dry weight, root length, root fresh and dry weight, crown fresh weight per plant, and shoot-to-root dry weight ratio. Data were analyzed using ANOVA, followed by LSD test to compare the means of treatment.
Results: Analysis of variance indicated that endophytic fungi significantly affected tiller number, shoot and root fresh and dry weight, crown fresh weight, and shoot-to-root dry weight ratio (P< 0.01), and root length (P< 0.05), but had no significant effect on leaf length. Salinity significantly influenced all traits except shoot-to-root dry weight ratio (P< 0.01). The interaction between endophyte presence and salinity was significant only for root dry weight (P< 0.05). Endophyte-infected plants exhibited improved traits compared to endophyte-free clones; for example, shoot dry weight was 1.14 g/plant in infected plants versus 0.70 g/plant in endophyte-free plants, representing a 1.5-fold increase. Root dry weight increased from 0.14 g/plant in endophyte-free to 0.36 g/plant in infected plants, a two-fold increase. Mean comparisons under different salinity levels indicated that tall fescue tolerated 0.5% NaCl well, but higher concentrations caused significant reductions in all traits. Shoot fresh weight decreased from 38.7 g/plant (control) to 26.1 g/plant (1.5% NaCl), and root fresh weight decreased from 5.46 g/plant (0.5% NaCl) to 1.87 g/plant (1.5% NaCl), a nearly threefold reduction. The endophyte × salinity interaction revealed that under high salinity, endophyte-infected plants maintained significantly higher root dry weight than endophyte-free plants (0.34 g/plant vs. 0.11 g/plant at 1% NaCl), indicating enhanced rooting capacity under stress.
Conclusion: Endophyte-infected tall fescue plants demonstrated improved tolerance to salt stress. The use of endophyte-infected tall fescue can enhance the sustainability of forage yield in areas with moderately saline soils and water.