Effects of Insect Herbivory and Fungal Endophyte Infection on Competitive Interactions among Grasses

Abstract

Interactions among plants may be influenced by pests or parasites that differentially affect one competitor. The purpose of this study was to determine the effects of fungal parasitism and insect herbivory, alone and in concert, on plant competitive interactions. The effects of fungal endophyte (Acremonium spp.) infection and fall armyworm (Spodoptera frugiperda) herbivory on competitive interactions in one-and two-species mixtures of the grasses tall fescue (Festuca arundinacea), red fescue (F. rubra), and perennial ryegrass (Lolium perenne) were examined in greenhouse experiments. In general, herbivory reduced plant biomass whereas endophyte infection increased plant biomass. Endophyteinfected (E+) plants were less damaged by herbivory than uninfected (E-) plants of the same species. Studies on fall armyworm larval feeding and choice tests with the five grass species were generally consistent with the outcome of the competition experiments; E+ plants were less nutritious and less preferred than E-plants of the same species. There were significant interactions among factors so that the outcome of competition depended on the species identities and the presence or absence of endophytes and herbivores. In competition with Kentucky bluegrass (Poa pratensis), E+ and E-perennial ryegrass produced similar biomass in the absence of herbivory, but E+ perennial ryegrass had nearly twice the biomass ofE-plants when herbivores were present. E+ and E-tall fescue were poor competitors with orchard grass (Dactylis glomerata) when herbivores were absent, but E+ tall fescue was a better competitor thanE-plants and orchard grass when herbivores were present. This study indicates that competitive hierarchies among grasses are altered by interactions with insect herbivores and fungal endophytes, which have typically been ignored in past studies.

Multistrain infections of the grass Brachypodium sylvaticum by its fungal endophyte Epichloë sylvatica

“…This phenomenon is particularly well documented in the agricultural grasses Festuca arundinacea and Lolium perenne infected by Neotyphodium endophytes where these metabolites cause toxicosis in cattle and sheep (Rowan, 1993 ;Bacon, 1995). Infected plants also often show enhanced growth and increased competitive abilities (Clay et al, 1993 ;Malinowski et al, 1997), as well as increased resistance to drought, pests and\or pathogens (Kimmons et al, 1990 ;Gwinn & Gavin, 1992 ;West, 1994 ;Schuster et al, 1995 ;Elbersen & West, 1996).…”

Endophytic microorganisms: a review on insect control and recent advances on tropical plants

“…Other types of interactions, taking into account a main host grass (Festuca or Lolium) and others grasses living in a common space, were conduced by Clay et al (1993), who analized changes resulting from these plant-plant interactions in insect control and presence of endophytic fungi. They analysed the effects of a member of the genus Acremonium in relation to attacks of S. frugiperda larvae to the tall fescue F. arundinacea and the red fescue F. rubra grown separately or mixed with other grasses.…”

Effects of Endophyte Infection in Tall Fescue (Festuca arundinacea: Poaceae) on Community Diversity

“…There have been several studies investigating both intraspecific and interspecific competition in F. arundinacea under controlled environmental conditions that have shown that infected plants are better competitors both with and without herbivory (Clay 1990a(Clay , 1997aHill et al 1991;Marks et al 1991;Clay et al 1993;Clay and Holah 1999). This may explain why attempts to establish endophyte-free pastures from highly uninfected seed have at times been unsuccessful as a few seeds in the mix will contain live endophytes.…”