Bitter-tasting Fescue Takes Over More Quickly With Help Of Plant-eating Bugs, Animals

In a 54-month study conducted at Indiana University, scientistsshowed that 'tall fescue,' a common variety that is infected with thesymbiotic fungus Neotyphodium coenophialum, tended to choke outuninfected fescue and native plant species. Tall fescue took over testplots much more quickly when herbivores had full access.

The research appears in the Aug. 30 issue of the Proceedings of the National Academy of Science.

"The practical implications of our findings are that the moreherbivores there are in an area, the more likely it will be thatinfected tall fescue grass will spread and suppress native plants,"said co-author Jennifer Rudgers, now an assistant professor of ecologyand evolutionary biology at Rice.

Fescue, which is native to the Mediterranean, covers anestimated 37 million U.S. acres. It is cultivated for grazing and isoften used as turf grass on lawns, golf courses and highwayrights-of-way. Ranchers do not typically cultivate tall fescue becausethe symbiotic fungus it carries, known as an endophyte, producesalkaloids that have negative health effects for livestock. It isestimated that 80 percent of U.S. fescue is endophyte-infected, and insome applications, like turf grass, it's the preferred variety.

Prior research on hereditary plant symbionts like the fescueendophyte have tended to look at plant-fungal pairings in isolation.Rudgers said she, post-doc advisor Keith Clay of Indiana University,and co-author Jenny Holah of George Mason University sought to get amore realistic picture of the ecological effects of symbiosis.

"We wanted to find out how the surrounding community affectedthe relationship between its host and its symbiont," she said. "Theimplications of the research are broad because it's estimated thatsimilar fungal symbionts exist in more than 20 percent of native U.S.grasses."

The tall fescue study was conducted on 60 plots nearBloomington, Ind., that measured 25 square meters apiece. At the startof the 4.5-year study, the land was plowed and planted with fescueseeds that sprouted alongside native grasses. Half of the seeds weretall fescue, which carries the fungal symbiont, and half did not carrythe symbiont. The fungus is not transmitted by insects or wind and isonly found in plants that sprout from infected seeds.

Half of the test plots were fenced to keep out foraginganimals, and half of the unfenced and fenced plots were sprayed with aninsecticide to suppress insect herbivores. Tall fescue progressed mostslowly in plots that were both sprayed and fenced, constituting about50 percent of live plant mass in the plots by study's end. In unfencedand unsprayed plots, tall fescue faired best, contributing to 75percent of the plot by study completion.

"Importantly, we found that more fescue in the unsprayed andunfenced plots was endophyte-infected compared to the plots withherbivore-reduction treatments," said Rudgers "This is significantbecause it shows that the herbivores actually drive an increase in therelative abundance of infected plants."

In follow-up studies, Rudgers plans to see how tall fescuefares against competitors under drought and non-drought conditions, andshe also plans to study symbiotic relationships in native grasses,including some Texas species.

The research was funded by the National Science Foundation.