Mutualistic asexual endophytes in a native grass are usually parasitic

Area of Science:

• Plant-microbe interactions
• Symbiotic relationships in grasses
• Fungal endophyte research

Background:

• Asexual systemic fungi in grasses are often considered mutualists, benefiting host plants.
• Evolutionary theory suggests symbionts relying on host transmission should benefit the host.
• Fungal endophytes in cultivated grasses enhance performance and defense, but this is less studied in native grasses.

Purpose of the Study:

• To test the assumption of mutualism for Neotyphodium endophyte infections in native Arizona fescue.
• To investigate the impact of endophyte infection on host grass growth, reproduction, and stress tolerance.
• To explore the role of host genotype and environmental factors in the endophyte-grass relationship.

Main Methods:

• A 3-year field experiment was conducted with Arizona fescue, controlling for host genotype.
• Soil moisture and nutrient levels were manipulated to simulate different environmental conditions.
• The effects of Neotyphodium infection on plant growth (volume, tillers, biomass) and reproduction (seed number, mass, germination) were measured.

Main Results:

• Neotyphodium infection generally decreased Arizona fescue growth, including plant volume, tillers, and biomass.
• Infected plants exhibited reduced reproductive output and lower seed germination success, indicating transgenerational negative effects.
• Host plant genotype significantly influenced growth and reproduction, often interacting negatively with endophyte presence.

Conclusions:

• The study challenges the prevailing notion that systemic asexual endophytes are always mutualists, particularly in native grass populations.
• Negative impacts of endophytes on host fitness suggest alternative hypotheses are needed to explain their persistence.
• Further research is required to understand the variable but high frequencies of endophyte infections in natural grass communities.