Fungal endophytes that colonize forest trees are widespread, but they are less well known than endophytes infecting grasses. The few studies on endophytes in trees mainly concern the tropical areas and the northernmost latitudes, while similar investigations in the Mediterranean region have so far been scarce and incidental. Endophytes are studied mostly in economically important forests suffering from diseases, such as oak forests. One common endophyte that has received some study on oak is the mitosporic Discula quercina. This paper, after first addressing some basic problems on tree endophytes, examines the ecology of D. quercina in Mediterranean oak stands. D. quercina is usually viewed as a symptomless colonizer of healthy Quercus cerris, infecting new leaves early in the growing season, in an unstable equilibrium between transient mutualism/neutralism and latent pathogenesis. It is postulated here that climatic factors can change the endophytic nature of D. quercina, turning it into a weak ...

https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-98-4-0380

Fungal endophytes in Mediterranean oak forests: a lesson from Discula quercina.

Vertically transmitted symbionts associate with some of the most ecologically dominant species on Earth, and their fixation has led to major evolutionary transitions (e.g., the development of mitochondria). Theory predicts that exclusive vertical transmission should favor mutualism and generate high frequencies of symbiosis in host populations. However, host populations often support lower‐than‐expected symbiont frequencies. Imperfect transmission (i.e., symbiont is not transmitted to all offspring) can reduce symbiont frequency, but for most beneficial symbionts it is unknown whether vertical transmission can be imperfect or during which life‐history stage the symbiont is lost. Using quantitative natural history surveys of fungal endophytes in grasses, we show that transmission was imperfect in at least one stage for all seven host species examined. Endophytes were lost at all possible stages: within adult plants, from adult tillers to seeds, and from seeds to seedlings. Despite this loss, unin...

https://www.jstor.org/stable/10.1086/589893

Symbiosis lost: imperfect vertical transmission of fungal endophytes in grasses.

Plant-associated microbes have been increasingly recognized for influencing host populations, plant communities, and even herbivores and predators. Thus, understanding factors that affect the distribution and abundance of microbial symbioses may be important for predicting the ecological dynamics of communities. Using endophytic fungi-grass symbioses, we explored how intrinsic traits of the symbiosis, specifically transmission mode, may influence symbiont frequencies in host populations. Combining published literature with new field surveys, we compared Epichloe endophytes, which had mixed horizontal and vertical transmission, with Neotyphodium endophytes, which were exclusively vertically transmitted from host plants to seeds. Exclusively vertical transmission should select against pathogenicity because symbionts depend entirely on hosts for reproduction. Across 118 host species, we found that Neotyphodium hosts had 40-130% higher symbiont frequencies than Epichloe hosts. In field surveys, endophyte frequency was positively correlated with the local density of hosts, but only for Epichloe, suggesting that contagiously spread Epichloe may attain higher frequencies when hosts are more abundant. Epichloe endophytes were also more likely than Neotyphodium to have imperfect vertical transmission; thus, hosts may reduce the transmission of more pathogenic symbionts to seeds. Results are consistent with the conclusion that the evolutionary transition to exclusively vertical transmission can alter patterns of symbiont frequency in nature.

A fungus among us: broad patterns of endophyte distribution in the grasses

Ryegrass staggers is a seasonal mycotoxicosis of grazing livestock characterised by tremors, in coordination and a staggering gait almost unaccompanied by physical lesions. Deaths occur only as a consequence of accident or starvation. Outbreaks, in summer and autumn, occur only on pasture in which endophyte (Neotyphodium lolii)-infected perennial ryegrass (Lolium perenne) predominates and usually on which animals are grazed intensively. Animals recover when moved to a different type of grazing or after rain has promoted pasture growth. The disease was recognised for 80 years before its cause was discovered as a consequence of a grazing trial of sheep on three ryegrass cultivars which happened to have three different levels of endophyte infection. The endophyte was first formally described as Acremonium loliae, later corrected to Acremonium lolii, and was finally placed in the genus Neotyphodium. It produces a number of secondary metabolites of which lolitrem B is the principal one causing ryegras...

A review of the Neotyphodium lolii / Lolium perenne symbiosis and its associated effects on animal and plant health, with particular emphasis on ryegrass staggers.

A new Epichloe species distributed in Africa, Europe, North America and South America on host genera Bromus, Festuca, Lolium and Poa is described. Stromata, characteristic of the genus, frequently occurred on the reproductive tillers of Poa secunda subsp. juncifolia, but neither perithecia nor mature asci were observed. Conidiogenous cells and conidial characteristics were in the range of Epichloe typhina. Regions of the genes encoding β-tubulin (tub2) and translation elongation factor 1-α (tef1) were amplified and sequenced. Phylogenetic analyses of these sequences grouped the Poa secunda subsp. juncifolia endophyte into one group within a non-hybrid Epichloe species complex. On the basis of morphology, host range and evolutionary history we propose that this endophyte represents a new species of Epichloe. The name Epichloe poae is proposed for this endophyte. The infectivity of the conidia produced on plants was evaluated. In the first experiment, using conidia of Epichloe poae from leaves and endophyte-free seeds of Poa secunda subsp. juncifolia we show that when germinating seeds and developing seedlings of the plant were exposed to conidia, 28–57 % of seedlings became infected by the endophyte. The non-inoculated control plants showed no colonization by the endophyte. In the following spring after vernalization, colonized plants on flowering culms produced stromata with conidia. In the second experiment, using stromal conidia and the same procedure, 19–42 % of seedlings of Poa secunda subsp. juncifolia became colonized by the endophyte. Our results demonstrate that Epichloe poae may spread to uninfected grass hosts by conidia frequently formed on the surfaces of plant leaves as well as by conidia formed on stromata.

Taxonomic placement of Epichloë poae sp. nov. and horizontal dissemination to seedlings via conidia

A polymerase chain reaction (PCR)-based method for detection of Neotyphodium endophytes in seed and plant tissue from tall fescue (Festuca arundinacea Schreb.), Italian (Lolium multiflorum Lam.), and perennial (Lolium perenne L.) ryegrasses was developed. The primers were designed to amplify products from a conserved region of the Neotyphodium spp. tubulin 2 gene which is present in N. coenophialum (Morgan-Jones and W. Gams) Glenn, C.W. Bacon, and Hanlin (endophyte of tall fescue), N. lolii (Latch, M.J. Chr., and Samuels) Glenn, C.W. Bacon, and Hanlin (endophyte of perennial ryegrass), and N. occultans C.D. Moon, B. Scott, and M.J. Chr. (endophyte of Italian ryegrass). PCR yielded the expected amplification products from infected seed lots for tall fescue (358 base pairs [bp]), Italian ryegrass (364 bp), and perennial ryegrass (370 bp). Based on DNA mixture tests and bulk seed analysis, the PCR assay was sensitive enough to detect as little as one infected seed per 50 seeds tested. In addition, the primer set detected the Neotyphodium spp. endophyte in all plant tissues except roots. Comparison of the PCRbased assay to microscopic examination and immunoblot detection of endophytes in seed lots showed that all three methods compared favorably to one another. However, none of the three methods could distinguish between viable and nonviable endophyte in seed. This PCR method provides an accurate, sensitive approach for detecting the presence of the endophyte in these grasses, while maintaining enough specificity to discriminate Neotyphodium spp. from related fungal contaminants such as ergot [Claviceps purpurea (Fr.:Fr.) Tul.].

A Sensitive PCR-Based Assay to Detect Neotyphodium Fungi in Seed and Plant Tissue of Tall Fescue and Ryegrass Species

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A Sensitive PCR-Based Assay to Detect Neotyphodium Fungi in Seed and Plant Tissue of Tall Fescue and Ryegrass Species