| Plant pathogens can have large effects on their host, including reduced host growth and fecundity. However, the effects of pathogens on clonal plants have rarely been studied, despite their prevalence in plant communities. I examined the effects of infection by the systemic fungus Epichloe glyceriae on the growth pattern, physiology, and clonal structure of the grass Glyceria striata in a series of greenhouse, field, and lab studies. I found that in the greenhouse infected Glyceria had greater clonal growth, both biomass and stolon production, than uninfected plants, although total biomass did not differ. This result indicates that resource allocation differed between naturally infected and uninfected plants. In a second experiment, I demonstrated that pathogen infection was responsible for altering host growth patterns by comparing the growth of infected and disinfected plants with the same host genotypes, which allowed me to decouple the effects of fungal infection and host genotype. I found that disinfected plants exhibited a reduction in clonal growth compared to their infected counterparts and had growth patterns similar to uninfected plants. I then looked at whether pathogen infection affected physiological integration and resource movement, specifically carbon, within clones. Physiological integration was not important, except for daughter ramet production in disinfected plants, where the loss of integration reduced daughter ramet production. The distribution of carbon within stolons did differ between infected and uninfected plants, with carbon sharing being greater along stolons of infected plants. In a final study, I examined the influence of infection on clonal structure (number of clones and spatial spread) of a natural Glyceria population. I found a high number of clones for both infected and uninfected plants. However, infected plants were more likely to be represented by a single ramet, indicating that they did not experience greater spatial spread, despite greater clonal growth in the greenhouse. With this set of experiments, I have shown that pathogen infection can have important consequences on hosts, quite separate from reductions in host growth and fecundity. |
