PARENT SESSION
Poster Session #62: Parasite-Host Interactions.
Thursday, August 8. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Shift of a Neotyphodium mutualism by a parasitic co-occurring endophyte.

Hayes, Cinnamon^*,1, Faeth, Stanley¹, ¹ Arizona State University, Tempe, Arizona

ABSTRACT- Neotyphodium endophytes are asexual symbiotic fungi that live intercelluarly within grass tissues. Well-documented benefits of infection on the host plant include enhanced growth, drought tolerance, nutrient uptake, and herbivore/pathogen resistance. Although these benefits are known for some agronomic grasses, the interaction between endophytes in native grasses is highly variable. Another systemic endophyte, the Phialophora-like endophyte (p-endophyte) usually co-occurs with Neotyphodium. However, the effects of dual infection are not clear. Sleepy grass (Achnatherum robustum) is a cool-season grass that is native to high elevations in the southwestern United States and often harbors both of these endophytes. Our hypothesis is that the p-endophyte shifts the interaction between Sleepy grass and Neotyphodium from mutualistic to parasitic. To test the costs and benefits of harboring these endophytes under different types of stress, we measured leaf senescence rates and total dry mass for plants of each infection status (uninfected, Neotyphodium infected, and co-infected). We examined these parameters under two watering regimens and 6 competition scenarios (each pair-wise combination of host infection status). Host infection status interacted with neighbor infection status to affect root biomass. Neotyphodium infected plants produced greater root mass than their co-infected neighbors. These results suggest that Neotyphodium may benefit the host plant, but also incurs a cost by allowing the co-symbiotic and parasitic p-endophyte to bypass host defenses. Thus, the benefits of Neotyphodium infection may be offset by the costs of increased susceptibility to a parasitic p-endophyte.

KEY WORDS: Neotyphodium , Phialophora -like, endophytes, Achnatherum robustum