Reduced herbivore resistance from a novel grass-endophyte association.
Abstract
Endophytic fungi in agricultural grasses confer agronomic advantages but can be detrimental to the health and production of grazing mammals. Attempts have been made to resolve this dilemma by creating novel associations of high-yielding grass cultivars and 'safe endophytes' that do not naturally co-occur. Recently, researchers created a novel association by combining a Moroccan strain of Neotyphodium coenophialum, called AR542, with the tall fescue Festuca arundinacea cultivar Georgia 5. This novel association is marketed commercially and has no doubt become naturalized; it is therefore important to assess its impact on other organisms. The bird-cherry-oat aphid Rhopalosiphum padi uses tall fescue as an alternative host. We assessed the performance of R. padi feeding on Georgia 5 that had been artificially infected with AR542, naturally infected by the common strain (CS) of N. coenophialum or was endophyte-free (EF). We cross-factored these three levels of endophyte infection with four levels of nitrogen fertilizer, and used two different methods of assessing aphid performance, clip-cages and enclosed populations. Endophyte-infected plants produced approximately 20% more dry mass than EF plants. In both the clip-cage and enclosed-population experiments, aphid populations grew fastest on the EF plants, slower on AR542-infected plants and slowest (or not at all) on the CS-infected plants. Synthesis and applications. Our results suggest that AR542 infection does not provide the same degree of protection from aphids as the commonly occurring CS infection. If similar results are found for other invertebrate herbivores, then the use of this novel endophyte association may be less useful than previously thought. The widespread conversion of tall fescue pastures, currently infected with the CS endophyte, to pastures infected with AR542 could result in a general increase in the prevalence of cereal aphids and, potentially, the diseases that they spread. However, such conversion might be beneficial to native invertebrate herbivores.