Artificial infection by endophytes affects growth and mycorrhizal colonisation of Lolium perenne

Fungal endophytes of the Clavicipitaceae live in aboveground parts of many grasses of temperate regions. Seedlings of two different cultivars of perennial ryegrass, Lolium perenne L., were artificially infected with one of two endophytes, Epichloe typhina and Neotyphodium lolii, or mock infected. The seedlings were then grown in a mixture of vermiculite and sand in the presence or absence of an inoculum of an arbuscular mycorrhizal fungus (Sclerocystis sp.). Ten weeks later, the plants were harvested and analysed with respect to mycorrhizal colonisation and shoot and root biomass. Endophyte-infected plants showed a significant decrease of mycorrhizal colonisation. This decrease was in some cases correlated with alterations of growth. Depending on the endophyte strains and on the mycorrhizal status, shoot-root biomass ratios were significantly affected. For both L. perenne cultivars, arbuscular mycorrhiza formation led to a higher shoot-root biomass ratio in N. lolii-infected plants and, conversely, to a lower shoot-root ratio in E. typhina-infected plants. These results indicate that effects of endophytes may be enhanced or counterbalanced in the presence of arbuscular mycorrhizal fungi.