Viruses in endophytes infecting natural populations of Festuca rubra

Resumen del trabajo presentado en el 4th International Neotyphodium/Grass Interactions Symposium, celebrado en Soest (Alemania), del 27 al 29 de septiembre de 2000
Festuca rubra is a very common grass in natural grasslands known as dehesas in Westem Spain. In these ecosysterns, about 70% of the F. rubra plants are infected by the fungal endophyte Epichloe festucae. In E. festucae cultures obtained frorn F. rubra plants, two double-stranded RNA (dsRNA) elernents have been found. The major elernent has a size of 5 kbp, and it is encapsidated. This dsRNA elernent is tought to be the genorne of a virus of the farnily Totiviridae. We call this virus Epichloe festucae virus (EN). The other dsRNA element, (refered as M) has a size of 2.5 kbp, it is not encapsidated, and has no nucleotide sequence homology with EfV. The presence of these dsRNAs cause no obvious symptorns in their fungal hosts. Efv and M are persistent in their host, and both elernents have been rnaintained in an isolate through succesive passes in laboratory media for more than two years. AIso, both elements are efficiently transrnitted frorn rnicelium to conidia by the process of conidiogenesis. When the incidence of endophytes and viruses in a natural population of Festuca rubra was studied, it was found that 78% (n=32) of the plants analized were infected by Epichloe festucae. Most isolates of E. festucae (82%) were infected by dsRNA viruses. However, some isolates were infected by both EfV and M while others were infected only by M. This suggests that the M elernent is not dependent upon EfV for its replication, and it is an autonomous replicon. The high incidence of these viruses in a population may indicate that all plants are infected by the same fungal genotype, or that in this population there is physical contact between different fungal genotypes. The dsRNA/Epichloe association mirrors the F. rubra/Epichloe association. In both cases ínfected hosts occur at a high frequency in natural populations and they do not show obvious symptoms.