Costs of fungal endophyte infection in Lolium perenne genotypes from Eurasia and North Africa under extreme resource limitation

Abstract

The effects of asexual, leaf-inhabiting endophytes on the growth of Lolium perenne are notoriously inconsistent and appear to be contingent on environmental conditions and host genetics. Both positive and negative growth effects of endophytes have been documented in some forage crop cultivars. Because they utilize host photosynthates, it is hypothesized that endophytes would impart a growth cost to infected plants under extreme resource limitation. The potential costs of infection by the fungal endophyte Neotyphodium lolii to its host grass, L. perenne, were investigated in accessions from Italy, Turkey, Morocco and Tunisia, the native part of the host's range. Four to five infected (+E) genotypes of L. perenne per accession were cloned into ramets, and the endophyte exterminated from half of the ramets (−E). Six +E and six −E ramets per genotype were grown for 5 months in a nutrient-poor substrate (vermiculite) within temperature- and light-controlled growth chambers. Accession and genotype within accession affected dry mass. Endophyte infection significantly reduced root:shoot ratio and the proportion of the shoot that was alive and photosynthetic. Relative interaction intensity indexes were negative for most genotypes, indicating host–endophyte associations were mostly parasitic. However, there were significant infection by genotype interactions; thus, endophyte-mediated effects depend on particular host genotype–endophyte combinations. This research is one of the few that have documented costs to endophyte infection in a grass–endophyte symbiosis. This cost, manifested as reduced root:shoot ratio and photosynthetic shoot fraction, was evident for infected L. perenne growing under conditions of extremely poor substrate nutrient availability.