First Report of Choke Disease Caused by Epichloë baconii in the Grass Agrostis castellana

Agrostis castellana is common in semiarid natural grasslands of the province of Salamanca, Spain. In this area, plants showing fungal stromata in their stems were observed in July of 2001. These symptoms are typical of choke disease, caused by Epichloë species in several grasses (3). In this disease, external fungal stromata develop around the leaf sheath of the flag leaf during the reproductive cycle of the plant host. As a result, the inflorescence does not emerge. In natural populations of A. castellana, less than 1% of plants showed disease symptoms, and all the stems of infected plants were sterilized by stromata. Intercellular endophytic mycelium was observed by microscopy in stem pith of diseased plants, but not on samples of 30 apparently healthy plants (1). Ergovaline, a fungal alkaloid, was not detected in lyophilized samples of infected plant tissue (2). In a fungal culture obtained from surface-disinfected leaf sheaths of a diseased plant (1), reniform conidia and conidiophores characteristic of the genus Epichloë were observed (4). To determine the fungal species, the nucleotide sequence of the ITS1-5.8SrRNA-ITS2 region and the three first introns of the beta-tubulin gene were obtained (EMBL Accession Nos. AJ490938 and AJ490939). When compared to those of other Epichloë species, these sequences identified the fungus from A. castellana as E. baconii (3). This fungus has been previously described as a pathogenic fungal endophyte in other Agrostis and Calamagrostis species (3,4). The fact that all stems of infected plants were diseased, infection incidence was low, and no alkaloids were detected in plants suggests that this grass-endophyte interaction is pathogenic and not mixed or mutualistic. References: (1) E. Clark et al. J. Microbiol. Methods 1:149, 1983. (2) N. Hill et al. Crop Sci. 33:331, 1993. (3) A. Leuchtmann et al. Mycol. Res. 102:1169, 1998. (4) J. White Jr. Mycologia 85:444, 1993.

Identification of the Fungal Endophyte Epichloe festucae in the Fine Fescue Festuca ampla

Festuca ampla is native to the Iberian Peninsula (4). Endophytic mycelium was observed by microscopy (2) in stem pith samples of two of eight asymptomatic plants of F. ampla collected in one population from a natural grassland in Salamanca, Spain. The fungus could be isolated (2) only from these two plants, and conidiophores and reniform conidia typical of Epichloe species (3) were observed in pure cultures. The two infected plants maintained in pots outside, developed ectostromata in some reproductive stems (choke disease) the year after the field sampling. Six seeds collected from an infected plant were germinated, and all six seedlings were found to be infected based on microscopy (2), implying seed transmission of the endophyte. These observations suggest that this is a pleiotropic symbiont, having both mutualistic and pathogenic states in its host. An ergovaline concentration of 120 ng/g dry weight was detected in a sample of leaves and leaf sheaths of an infected plant. All of the above characteristics are typical of the genus Epichloe, and in particular of the fine fescue endophyte E. festucae (1,3). To determine the species, internal transcribed spacer and 5.8-rDNA sequences as well as a partial sequence of the β-tubulin gene were obtained. These two sequences (EMBL Accession Nos. AJ488497 and AJ488498) showed 100% sequence homology to the corresponding sequences in E. festucae. To our knowledge, this is the first report of this endophyte species in the grass F. ampla. References: (1) L. P. Bush et al. Plant Physiol. 114:1, 1997. (2) E. M. Clark et al. J. Microbiol. Methods 1:149, 1983. (3) A. Leuchtmann et al. Mycologia 86:802, 1994. (4) I. Markgraff-Dannenberg. Festuca. Pages 125-153 in: Flora Europaea, Vol 5. Cambridge University Press, Cambridge, 1980.

Genetic structure of natural populations of the grass endophyte Epichloë festucae in semiarid grasslands

Plants of red fescue (Festuca rubra), a commercially important turf grass, are infected by the fungal endophyte Epichloë festucae in semiarid natural grasslands, known as dehesas, in western Spain. We used amplified fragment length polymorphism (AFLP) markers to analyse the genetic polymorphism existing in two natural populations of Epichloë festucae. Linkage disequilibrium and the presence of clonal lineages indicated that nonrecombinant asexual reproduction predominates in both populations. However, most genetic variation detected was found to occur within populations, with only a moderate amount of genetic differentiation between populations (F(ST): 0.197). Overall, the study suggests that dehesa grasslands are useful reservoirs of Epichloë festucae endophytes, and provides information on population structure which is relevant to design sampling strategies.