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Plants employ various strategies to mitigate the impact of herbivory and one such strategy involves the associations with fungal endophytes. Some cool‐season forage grasses benefit from protection against herbivores by Epichloë fungal endophytes. However, since the maintenance of symbiosis relies on the plant, costs of hosting endophytes have been also observed. This becomes particularly crucial when forage varieties, inoculated with endophytes that are nontoxic to livestock but still protect host against insect herbivores, experience significant foliage loss (defoliation). We investigated the impact of a nontoxic Epichloë endophyte on the responses of tall fescue plants to defoliation across two morphotype varieties, Continental and Mediterranean, and different seasonal contexts. Under specific defoliation treatments, endophyte‐symbiotic plants showed reduced postdefoliation recovery, indicating the costs of hosting the endophyte for host plants. However, these conditions were not the most severe for plant growth. Regardless of the endophyte's presence, plants from Continental morphotype exhibited superior recovery than those from Mediterranean morphotype, an effect that was more pronounced in summer. Notably, the endophyte promoted plant growth after defoliation in winter for both morphotypes. Our study offers insights into mitigating endophyte‐associated costs on plant recovery postdefoliation by strategically managing cutting intensity and frequency, considering the seasonal variation. [ABSTRACT FROM AUTHOR]

Natural grassland ecosystems are increasingly threatened by excessive loadings of nutrients and by the presence of species bred for high productivity. By manipulating grazing regimes and nutrient availability, agricultural practices facilitate the establishment and spread of certain forage plant species outside managed landscapes, challenging local biodiversity. The ecological success of some species in the invaded range sometimes seems to be associated with the symbiosis with foliar fungal endophytes. Symbiotic fungi may increase the competitiveness of host species, but also the resistance to herbivory through the production of toxic secondary compounds such as alkaloids. While progress has been made in understanding how soil nutrients modulate other benefits offered by fungal endophytes to plants (e.g. stress tolerance, competitive ability, etc), the consequences for a higher trophic level (i.e. herbivores) and the potential feedbacks on plant invasion have not been explored yet.We explored the relative and interactive importance of soil nitrogen (N) and phosphorus (P) in modulating the interaction of the invasive grass tall fescue—associated with fungal endophytes—and native herbivores in a natural grassland. We hypothesized that N and P nutrients modulate differentially leaf quality traits, namely nutritional value and fungal alkaloid contents, determining the level of damage by native insect herbivores on the exotic tall fescue.We found that only the addition of P significantly increased native caterpillar density in the field, which corresponded to a concomitant increase in leaf damage. In contrast to expectations, the concentration of the alkaloid ergovaline in leaves was not strongly related to N. It was the level of soil P which dictated the concentration of the element (P) in the leaves and reduced the level of defence against herbivores in this endophyte‐symbiotic species. Then, herbivore performance increased, and plants were more prone to be attacked.Synthesis. Our study indicates a strong control of soil P fertility on the triple interaction among plants, fungal endophytes and native herbivores. This highlights the potential role of increased soil nutrients on the invasion spread of endophyte‐symbiotic forage plants in natural grasslands. [ABSTRACT FROM AUTHOR]

Highlights: [•] Symbiotically modified organisms (SMOs) can improve grass yield, and resistance to pests and weeds. [•] SMOs can improve forage quality for livestock. [•] Toxicity can be caused by uncharacterized plant or fungal metabolites. [•] Feasibility of SMOs depends on the cultivar and fungal strain. [ABSTRACT FROM AUTHOR]

Neotyphodium frequently occurs as an endophyte in grasses. Evidence shows enhanced fitness of endophyte infected grasses relative to non-infected ones. Some studies of seed germination show endophyte enhancement of plant fitness in various environments, but inconsistent results indicate that further studies are needed. So far, experiments have failed to separate the confounded effects of population origin and seed management. For this reason, we evaluated the effects of endophyte infection on seed dormancy and germination in Lolium multiflorum using an experimental design controlling these factors. Depending on the year of seed production, endophyte infection modified seed response to light quality, affecting predominantly seed dormancy levels. Nevertheless, the endophyte did not affect base temperature or thermal time of germination. We concluded that endophytes were not a strong influence on germination behaviour. We speculate from our results that the presence of the endophyte changes germination by an indirect effect, in extending growth of the maternal plant during seed development and ripening. The direct effect of hyphae in the seed on seed behaviour was disregarded, because the difference between infected and non-infected seed varied within the year of seed production. Future experiments should focus on effects of the endophyte on the canopy of parent plants during seed production and ripening, and, hence, on subsequent dormancy and germination of the seeds. [ABSTRACT FROM AUTHOR]