A Test for Constitutive and Induced Resistance by Tall Fescue (Festuca arundinacea) to an Insect Herbivore: Impact of the Fungal Endophyte, Acremonium coenophialum

Abstract

-Endophytic fungi living within some grasses have been shown to increase resistance of their host plants to insect herbivores. We tested the hypothesis that endophytes also mediate induced resistance by a grass to an herbivorous insect. Tall fescue (Festuca arundinacea), both infected and uninfected with the endophyte, Acremonium coenophialum, was artificially damaged by clipping a tiller from each plant four weeks after germination. We used the fall armyworm (Spodoptera frugiperda) as a bioassay to determine the affects of our treatments. Fall armyworm larvae were reared by feeding them shoot and stem material of damaged and undamaged plants in a two factor (infection status and damage) design. Eight-day-old larvae weighed less and took longer to develop into adults when fed endophyteinfected vs. endophyte-free plant material. However, the interaction between status and damage was not statistically significant. In contrast, pupae weighed more when fed infected vs. endophyte-free plant material and the interaction between infection status and damage had a marginally significant effect on pupal mass (F1,177 = 32.2; P = 0.05). Pupae reared from damaged infected plants weighed less than those reared from undamaged infected plants. No pattern with damage was apparent for insects reared on endophyte-free plants. Our results suggest that the clipping damage may result in an induced response in plants infected with the fungal endophyte.