Presence of Epichloë Fungus in the Endosperm-Side of the Seed Predicts the Symbiotic Status of the Seedling

Abstract

Some important forage grasses of the genera Festuca and Lolium establish persistent symbiotic associations with vertically-transmitted fungal endophytes (genus Epichloë). In certain cases, the fungus causes livestock diseases due to fungal toxins that accumulate in the plant biomass. Killing the fungus in the seed is a possibility for getting rid of the problem. However, since the symbiosis is mutualistic, the inoculation of elite cultivars with non-toxic but still benefcial endophytes is a current breeding strategy. Additionally, the symbiosis has become a model system to study in ecology and evolution, where the manipulation of the symbiotic status of plants is critical for the experiments. In this study, we confrmed that testing for the endophyte?s presence or absence in the endosperm-side of the seed was a reliable predictor of the symbiotic status of the seedling. We built on this previously proposed concept by (i) estimating the high correspondence between the infection status in one side of the seed (either + or −) and the infection status of the other side, and (ii) demonstrating that cutting the seed in two halves did not afect seed germination, normal seedling growth, nor the endophyte transmission to the seedling. We also showed that cutting the seed reduced seedling size, an impact that increased with endophyte presence provided the fungus was alive. Te strengths and weaknesses of the technique, as well as its potential use in other species, are discussed.