Infection by the systemic fungus Epichloë glyceriae alters clonal growth of its grass host, Glyceria striata

Abstract

Parasites and pathogens are hypothesized to change host growth, reproduction and/or behaviour to increase their own transmission. However, studies which clearly demonstrate that parasites or pathogens are directly responsible for changes in hosts are lacking. We previously found that infection by the systemic fungus Epichloë glyceriae was associated with greater clonal growth by its host, Glyceria striata. Whether greater clonal growth resulted directly from pathogen infection or indirectly from increased likelihood of infection for host genotypes with greater clonal growth could not be determined because only naturally infected and uninfected plants were used. In this study, we decoupled infection and host genotype to evaluate the role of pathogen infection on host development and clonal growth. We found that total biomass production did not differ for clones of the same genotype, but infected clones allocated more biomass to clonal growth. Disinfected clones had more tillers and a greater proportion of their biomass in the mother ramet. Infected clones produced fewer tillers but significantly more and longer stolons than disinfected clones. These results support the hypothesis that pathogen infection directly alters host development. Parasite alteration of clonal growth patterns might be advantageous to the persistence and spread of host plants in some ecological conditions.

Epichloë glyceriae infection affects carbon translocation in the clonal grass Glyceria striata

“…The generation of disinfected plant material is described in detail in Pan and Clay (2003). Briefly, two infected plants were used from each of two populations in southern Indiana, USA: Beaver Bog (BE, Owen County) and Thomson Park (TH, Monroe County).…”

“…obs). Infected plants also have greater clonal growth, both number of stolons and clonal growth biomass, than disinfected plants, but total above-ground plant biomass was the same (Pan & Clay, 2003). For a more detailed description of the natural history of the E. glyceriae-G. striata system, see Pan & Clay (2002).…”

“…Epichloë species typically have both pathogenic and mutualistic effects on their host grasses (Clay & Schardl, 2002). In previous studies, we found that E. glyceriae had a positive effect on G. striata clonal growth, increasing both number of stolons and clonal growth biomass, although total biomass did not differ between infected and uninfected plants (Pan & Clay, 2002, 2003. Despite more vigorous vegetative growth, host plants infected by Epichloë endophytes are often completely sterilized by infection (Clay & Schardl, 2002), leading Bradshaw (1959) to refer to these interactions as 'a curious form of symbiosis'.…”

“…Clonal plants infected by parasites and pathogens also experience reduced growth, survivorship, and reproduction (Nus & Hodges, 1990;Frantzen, 1994;D'Hertefeldt & van der Putten, 1998;Piqueras, 1999, but see Wennström, 1994;Pan & Clay, 2002, 2003. However, how they affect the physiology of clonal plants is not well understood.…”

“…All tillers were propagated under fungicide-free conditions for at least five tiller generations to minimize residual treatment effects. Disinfected plants had growth patterns similar to uninfected plants (Pan & Clay, 2002, 2003. Before use in this experiment, all tillers were examined microscopically to determine infection status (Bacon & White, 1994).…”