Document: STA-3-54-6

Mutualism gone awry? Asexual endophytic fungi in native grasses.

FAETH, S.H.* and T.J.SULLIVAN

Arizona State University, Tempe, AZ 85287-1501, USA ¹

Abstract:
Endophytic fungi are thought to interact mutualistically with their host grasses mainly by increasing resistance to herbivores, as well as by increasing drought resistance, germination success, competitive abilities and deterring seed predators. Further, endophytic fungi have been proposed as major factors in driving plant community diversity, despite their relatively low biomass and cryptic nature. However, most of these mutualistic and biodiversity effects have been documented only for agronomic grasses, non-native herbivores, and mostly introduced plant species. There are few studies of the interaction of endophytes in native grass populations and communities. We tested several hypotheses to explain the consistently high but variable frequency of Neotyphodium infections in natural populations of Arizona fescue. We found no pattern of increased infection frequency with increased grazing as predicted by the mutualistic hypothesis. Furthermore, in field and greenhouse experiments, the presence of the endophyte did not decrease, and sometimes increased, preference and preformance of native and non-native invertebrate herbivores. Generally, plant genotype swamped the effects of the endophyte on both herbivore and host performance. In experiments with infected and uninfected seeds where plant genotype was strictly controlled, infected seeds had lower germination success and increased seddling mortality from fungal pathogens, contrary to predictions based upon Neotyphodium as a grass mutualist. Finally, we found only a weak relationship between endophyte frequency and diversity of native plant species. Our results suggest that the purported mutualism between endophytes and host grasses, and the effects of endophytes on plant community structure, are not universal. Alternative explanations are necessary to explain the high, but variable frequency of endophytes in natural grass populations.

Keywords: fungal endophytes, grasses, mutualism, Neotyphodium

This abstract is being presented at: 11:15 AM in session:
Oral Session #5: Mutualisms.