Incidence of viruses in antural populations of the grass endophyte Epichloë festucae

Abstract

Epichloe festucae is a fungal endophyte which infects the grass Festuca rubra. In most cases, infected plants show no symptoms, and increased resistance to insects and better performance under abiotic stresses have been observed in infected plants. Two different virus-like agents have been identified in isolates of Epichloefestucae. An spherical particle of 50 nm in diameter contains a 5 kbp double-stranded RNA genome, while a smaller 2.5 kbp dsRNA segment is not encapsidated. We have identified isolates infected by each virus-like agent as well as by both. In all cases, infected isolates show no obvious symptoms. In natural grasslands of Western Spain, about 70% ofthe Festuca rubra plants are infected by Epichloefestucae. In an study done in two populatíons of red fescue, it was found that the frequencies of viral infection in Epichloe festucae isolates were of 67 and 85%. Since not aH the infected isolates are the product of clonal propagatíon of the same fungal genotype, and transrnission by anastomosis ís the only known mechanism of transrnission for fungal viruses, it is likely that the viruses are transmitted by contact among fungal isolates. This grass-fungus-virus relationship appears to be a three-way symbiosis