Effects of endophytic fungi on the phenotypic plasticity of Lolium perenne (Poaceae)

The effects of high vs. low levels of endophytic fungi on the phenotypic plasticity of cloned genotypes were examined in perennial ryegrass (Lolium perenne L.). The objectives were to determine whether endophytic fungi influence plastic responses of host genotypes to variable soil nutrients and whether or not endophyte infection and host genotype interact to determine the extent of this plasticity. Twelve infected genotypes were cloned into ramets: half the ramets were treated with the systemic fungicide Benomyl to reduce or eliminate the endophyte, while the other half were untreated. Ramets of each genotype were subjected to high, medium, or low levels of nutrients in the greenhouse for 11 wk. Tiller number, leaf area, and leaf mass were determined after 11 and 25 wk. The fungicide significantly reduced the level of endophyte infection. Responses to nutrient conditions in relation to fungicide treatment were genotype specific: for some genotypes, high levels of endophytic fungi appeared to reduce plasticity, while for other genotypes the endophyte had no effect. The potential for microscopic symbionts to affect phenotypic plasticity in genetically variable populations has not often been recognized. However, the clandestine effects of symbionts on the plasticity of host genotypes could impact microevolutionary processes occurring within plant populations that occupy heterogeneous environments.