Spontaneous in planta changes in fungal endophytes impact symbiosis

Abstract

The symbiosis between the asexual Ascomycetous fungi of the genus Neotyphodium and host grasses is considered to be symptomless. Symbioses involving Epichloë can show symptoms but this is restricted to the formation of stroma on floral structures. Fungal mycelium of both Epichloë and Neotyphodium endophytes occupy the intercellular space of plant tissues with no breach of host cell walls. Research involving these endophytes and their host grass symbioses relies on staining of host tissues and microscopic examination, immuno-detection or in-vitro isolation to determine infection status. This work reports on the observation of two independent instances of spontaneous change in the endophyte fungus that manifests as changes in the host grass vegetative morphology; one involving a genetically modified Epichloë festucae inoculated into a perennial ryegrass (Lolium perenne) population and the other a resident wild type Neotyphodium lolii. The relationship between wild type and variant fungus is confirmed as is the connection between variant fungus and host morphology. This work demonstrates that spontaneous in-planta changes in fungal endophytes occur and that these can impact on fungus/host grass symbioses. Keywords: Neotyphodium, Epichloë, symbiosis, endophyte, perennial ryegrass