The fungus Clonostachys epichloe alters the influence of the Epichloe endophyte on seed germination and the biomass of Puccinellia distans grass

The fungal grass endophyte Epichloe typhina (Pers.) Tul. & C. Tul. (Ascomycota: Clavicipitaceae) grows intercellulary in aerial plant parts and reproduces asexually by invading host seeds. In this phase, it enhances seed production and germination, which accelerates its vertical spread. This relationship may be distorted by other seed-born fungi, whose spread is not so directly dependent on the success of the grass. Recently, the fungus Clonostachys epichloe Schroers has been observed on Puccinellia distans (Jacq.) Parl seeds originating from grass clumps infested with stromata, sexual structures of Epichloe typhina that are formed in spring on some host culms, preventing flower and seed development ('choke disease'). C. epichloe shows mycoparasitic activity toward Epichloe stromata by reducing the production of ascospores, which are responsible for horizontal transmission of the fungus. The aim of this study was to investigate the effect of seed-borne C. epichloe on seed germination, as well as the size and weight of P. distans seedlings and to examine whether C. epichloe alters the influence of Epichloe in the early developmental stages of P. distans. The results showed that if C. epichloe acts on seeds together with E. typhina endophytes, the seeds were negatively affected due to the elimination of the positive effect of the latter in terms of both seed germination rate and seedling length. At the same time, C. epichloe increased the proportion of E. typhina-untreated germinated seeds. Additionally, only the joint action of the two fungi, E. typhina and C. epichloe, effectively stimulated seedling dry mass; the presence of E. typhina alone was not sufficient to noticeably affect seedling size. Based on the increasing commonality of C. epichloe on Epichloe stromata, as well as its potential to be used in biocontrol of 'choke disease', we should take a closer look at this fungus, not only in terms of its mycoparasitic ability, but also in terms of its cumulative impact on the whole Epichloe-grass system.

Automated summary

The fungal grass endophyte Epichloe typhina enhances seed production and germination, promoting its vertical spread. However, the presence of another seed-born fungus, Clonostachys epichloe, on these seeds can negatively affect seed germination and seedling length by eliminating the positive effects of Epichloe. Only the joint action of Epichloe and Clonostachys effectively stimulated seedling dry mass. It is important to further study the impact of Clonostachys on the Epichloe-grass system.