Search

Background and aims: Host-specific Epichloë spp. are endophytic fungal symbionts of pooid grasses that produce herbivore-deterring alkaloids and alter the host's metabolite and protein profiles. Early observations suggested that Epichloë may have negative allelopathic effects on neighbouring plant species, particularly Trifolium spp. clovers, but subsequent allelopathy experiments produced variable results. We examined two hypotheses: (1) Epichloë strains differ in allelopathic effect, and (2) Epichloë allelopathy negatively affects other plant species. Methods: We performed a greenhouse experiment using root exudates from Lolium perenne L. hosting different E. festucae var. lolii (Latch, M.J. Chr. & Samuels) C.W. Bacon & Schardl strains to compare their allelopathic effects on native legumes and forbs. We then used meta-analysis to examine the evidence to date for allelopathic effects of Epichloë endophytes. Results: We found little difference in effect among E. festucae var. lolii strains and very little evidence for negative allelopathic effects of Epichloë in cool-season grasses across a range of methodologies, target plant species, and response measures. Negative allelopathic effects were detected only for root hair measures, which were from a single study. Positive effects on biomass were found for some experimental subgroups, including legumes. However, the majority of response variables showed no evidence for Epichloë allelopathy. Conclusions: Although there is currently little evidence for negative Epichloë allelopathic effects, our meta-analysis identified several research gaps. Experiments testing the functional belowground effects of Epichloë presence may help to determine its effects on non-host plant performance via plant-soil feedbacks. [ABSTRACT FROM AUTHOR]

Strictly vertically transmitted (hereditary) Epichloë spp. fungal endophytes are symbionts with cool-season pooid host grasses. Such endophytes may increase host invasiveness in the non-native, introduced ranges. However, because costs and benefits for the host can vary with the growing conditions, the endophyte may become locally or temporally extinct when costs outweigh benefits. Our long-term field experiment involved the introduction of seven Schedonorus pratensis (meadow fescue) cultivars hosting Epichloë uncinata endophyte, which represent host-grass populations differing in genetic backgrounds and Epichloë infection frequencies, to an unmanaged old field. In the first 6 years, the host grasses persisted but did not become invasive in the plant community, regardless of their endophyte infection frequency. Subsequently, we hypothesized that increasing nutrient availability would decrease endophyte costs and thus increase the host's success and abundance. We fertilized half of the plots for four additional years and re-examined S. pratensis invasiveness. We predicted that increased nutrient availability would increase S. pratensis abundance and E. uncinata frequency and concentration, as well as decrease plant community diversity, relative to unfertilized plots. Fertilization increased endophyte concentrations in three low-endophyte host populations. However, E. uncinata did not enable S. pratensis populations to achieve high abundance or to reduce plant community diversity in the old field, with or without fertilization. Thus, nutrient availabililty and host invasiveness appear to be decoupled in this study system. [ABSTRACT FROM AUTHOR]

Background. Plants possess a sophisticated immune system to defend from herbivores. These defence responses are regulated by plant hormones including salicylic acid (SA) and jasmonic acid (JA). Sometimes, plant defences can be complemented by the presence of symbiotic microorganisms. A remarkable example of this are grasses establishing symbiotic associations with Epichloë fungal endophytes. We studied the level of resistance provided by the grass' defence hormones, and that provided by Epichloë fungal endophytes, against an introduced herbivore aphid. These fungi protect their hosts against herbivores by producing bioactive alkaloids. We hypothesized that either the presence of fungal endophytes or the induction of the plant salicylic acid (SA) defence pathway would enhance the level of resistance of the grass to the aphid. Methods. Lolium multiflorum plants, with and without the fungal endophyte Epichloë occultans, were subjected to an exogenous application of SA followed by a challenge with the aphid, Sipha maydis. Results. Our results indicate that neither the presence of E. occultans nor the induction of the plant's SA pathway regulate S. maydis populations. However, endophytesymbiotic plants may have been more tolerant to the aphid feeding because these plants produced more aboveground biomass. We suggest that this insect insensitivity could be explained by a combination between the ineffectiveness of the specific alkaloids produced by E. occultans in controlling S. maydis aphids and the capacity of this herbivore to deal with hormone-dependent defences of L. multiflorum. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ecology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Initial studies of grass-endophyte mutualisms using Schedonorus arundinaceus cultivar Kentucky-31 infected with the vertically transmitted endophyte Epichloë coenophiala found strong, positive endophyte effects on host-grass invasion success. However, more recent work using different cultivars of S. arundinaceus has cast doubt on the ubiquity of this effect, at least as it pertains to S. arundinaceus- E. coenophiala. We investigated the generality of previous work on vertically transmitted Epichloë-associated grass invasiveness by studying a pair of very closely related species: S. pratensis and E. uncinata. Seven cultivars of S. pratensis and two cultivars of S. arundinaceus that were developed with highor low-endophyte infection rate were broadcast seeded into 2 9 2-m plots in a tilled, old-field grassland community in a completely randomized block design. Schedonorus abundance, endophyte infection rate, and co-occurring vegetation were sampled 3, 4, 5, and 6 years after establishment, and the aboveground invertebrate community was sampled in S. pratensis plots 3 and 4 years after establishment. Endophyte infection did not enable the host grass to achieve high abundance in the plant community. Contrary to expectations, high-endophyte S. pratensis increased plant richness relative to low-endophyte cultivars. However, as expected, high-endophyte S. pratensis marginally decreased invertebrate taxon richness. Endophyte effects on vegetation and invertebrate community composition were inconsistent among cultivars and were weaker than temporal effects. The effect of the grass-Epichloë symbiosis on diversity is not generalizable, but rather specific to species, cultivar, infection, and potentially site. Examining grass-endophyte systems using multiple cultivars and species replicated among sites will be important to determine the range of conditions in which endophyte associations benefit host grass performance and have subsequent effects on co-occurring biotic communities. [ABSTRACT FROM AUTHOR]

Fungal endophytes in cool-season grasses may affect communities at multiple trophic levels. However, it is unclear whether community-scale endophyte effects arise due to the endophyte itself or as a result of unique, endophyte-host interactions. We used a long-term field experiment to test whether common-toxic (CT) and non-ergot alkaloid-producing (novel) endophytes in Schedonorus arundinaceus (tall fescue) forage cultivars consistently affect communities across tall fescue hosts. Tilled plots (2 × 2 m; Guelph, ON) were seeded with Georgia 5 and Jesup cultivars containing either the CT or AR542 (novel) endophyte and allowed to be re-colonized by plant species from the local propagule pool. Non-seeded control plots were included to assess effects of seeding the non-native grass. We assessed plant, invertebrate, soil moisture, and soil nutrient responses to the endophyte-cultivar treatments after four growing seasons. Seeding tall fescue affected plant species abundances, but not richness, and did not consistently alter soil moisture and nutrient pools. Endophyte identity in the tall fescue cultivars affected the communities, but effects were not consistent between cultivars. Within Georgia 5, the AR542 endophyte reduced tall fescue abundance and altered the invertebrate community relative to CT plots. Within Jesup, the AR542 endophyte reduced species evenness and decreased soil moisture during dry periods relative to CT plots. Endophyte effects were not consistent between cultivars, and it is probable that the community-scale effects of endophyte infection in tall fescue cultivars arise due to unique interactions between cultivar and endophyte. [ABSTRACT FROM AUTHOR]

Despite their ubiquitous nature, interactions between multiple micro-organisms and their effects on host growth and each other's success have received limited scientific attention. In particular, grasses can be commonly infected by both endophytic fungi and viruses, which are typically transmitted by aphids. In this study, we investigated how an aphid-transmitted viral pathogen and a symbiotic endophytic fungus altered host growth and allocation. We hypothesized that, by reducing aphid feeding, endophyte infection would lower viral titre and consequently decrease the negative effects of virus infection on host biomass production., In a greenhouse experiment, we manipulated fungal endophyte status and virus infection ( Barley Yellow Dwarf Virus - PAV) of two tall fescue cultivars with different genetic backgrounds [KY 31 and pasture demonstration farm (PDF)]. In one cultivar (PDF), we also manipulated endophyte strain, using two strains that had been selected for differences in alkaloid production. We assessed host, virus and vector responses., As hypothesized, endophyte infection decreased reproduction and abundance of aphid vectors; however, in contrast to our hypothesis, this response by aphids did not impact viral titre. For both tall fescue cultivars, endophyte infection alleviated the negative effect of virus infection on the proportion of total plant biomass allocated to roots. On the other hand, for the KY 31 cultivar only, virus infection decreased tillering in endophyte-infected individuals, but not endophyte-free individuals. Within the PDF cultivar, both endophyte strains produced similar effects on host, virus and vector responses., Synthesis These results indicate that some of the beneficial effects provided by endophyte infection, particularly alleviating the negative effect of virus infection on the proportion of total plant biomass allocated to roots, do not arise strictly from altering host interactions with herbivores (aphids), but also occur by changing host responses to viral infection. Furthermore, these results emphasize the importance of exploring multispecies microbial interactions and genetic controls on these interactions in order to more fully understand their role in community- and ecosystem-level dynamics. [ABSTRACT FROM AUTHOR]

Cultivars of several cool-season grasses used in forage and turf applications are developed to contain low (E−) or high (E+) seed fungal endophyte presence, and these characteristics may influence their competitive ability and effects on communities., We established a long-term field experiment to test the predictions that Schedonorus arundinaceus ( SA) tall fescue forage cultivars differ in their effects on communities from turf cultivars and that E+ cultivars differ in their effects on communities from E− cultivars. Two of the three E+ turf cultivars were low endophyte, and turf cultivars were therefore defined as 'E+ history' and 'E− history'., Forage (E−) plots contained more SA than turf (E− history) plots and differed in community structure and function from turf (E− history) plots. Cultivar identity also influenced community structure and function in pairwise comparisons between forage (E−) and turf (E− history) plots., Within the forage cultivars, E+ plots contained more SA and were marginally less dominated by other grasses than E− plots, but these differences were not consistent in comparisons between specific E+ and E− forage cultivars. Moreover, E+ and E− forage plots were similar in other aspects of community structure and function, indicating that a cultivar's endophyte status does not consistently determine its effects., Despite low endophyte presence in two of three cultivars, E+ history turf plots differed in measures of composition, structure and nutrient cycling from E− history turf plots, indicating that there are genetic differences between E+ and E− cultivars which can influence their effects on communities., Synthesis and applications. Schedonorus arundinaceus cultivars vary in their competitive ability and effects on communities, and this variation may be explained by the application for which the cultivars were developed, their endophyte status and genetic differences among cultivars within application categories. We recommend preferentially selecting cultivars developed for turf applications and cultivars with low seed endophyte presence to minimize negative effects of seeding a non-native grass on communities. However, final selections should be based on common trial performances because genetic differences between cultivars will affect their performance independently of their application category and endophyte status. [ABSTRACT FROM AUTHOR]

Lolium perenne cultivars differing in their capacity to accumulate water soluble carbohydrates (WSCs) were infected with three strains of fungal Neotyphodium lolii endophytes or left uninfected. The endophyte strains differed in their alkaloid profiles. Plants were grown at two different levels of nitrogen (N) supply in a controlled environment. Metabolic profiles of blades were analyzed using a variety of analytical methods. A total of 66 response variables were subjected to a principle components analysis and factor rotation. The first three rotated factors (46% of the total variance) were subsequently analyzed by analysis of variance. At high N supply nitrogenous compounds, organic acids and lipids were increased; WSCs, chlorogemc acid (CGA), and fibers were decreased. The high-sugar cultivar 'AberDove' had reduced levels of nitrate, most minor amino acids, sulfur, and fibers compared to the control cultivar 'Fennema', whereas WSCs, CGA, and methionine were increased. In plants infected with endophytes, nitrate, several amino acids, and, magnesium were decreased; WSCs, lipids, some organic acids, and CGA were increased. Regrowth of blades was stimulated at high N, and there was a significant endophyte X cultivar interaction on regrowth. Mannitol, a fungal specific sugar alcohol, was significantly correlated with fungal biomass. Our findings suggest that effects of endophytes on metabolic profiles of L. perenne can be considerable, depending on host plant characteristics and nutrient supply, and we propose that a shift in carbon/N ratios and in secondary metabolite production as seen in our study is likely to have impacts on herbivore responses. [ABSTRACT FROM AUTHOR]