Symbiotically modified organisms: nontoxic fungal endophytes in grasses

• 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.

We propose that symbiotically modified organisms (SMOs) should be taken into account in sustainable agriculture. In this opinion article, we present the results of a meta-analysis of the literature, with a particular focus on the potential of SMOs in forage and turf grass production, to determine the impact of endophytes in grasses on livestock, the grassland ecosystems, and associated environments. SMOs can be incorporated into breeding programs to improve grass yield, resistance to pests and weeds, and forage quality for livestock by decreasing the level of toxic alkaloids. However, the benefits of these selected grass–endophyte symbiota appear to be highly dependent on grass cultivar, fungal strain, and environmental conditions, requiring a comprehensive understanding of the genetic bases and phenotypic plasticity of the traits of the plant–microbe unit in different environments.