The Effects of Endophytes on Seed Production and Seed Predation of Tall Fescue and Meadow Fescue

Fungal endophytes of grasses are often included in agricultural management and in ecological studies of natural grass populations. In European agriculture and ecological studies, however, grass endophytes are largely ignored. In this study, we determined endophyte infection frequencies of 13 European cultivars and 49 wild tall fescue (Schedonorus phoenix) populations in Northern Europe. We then examined seed production and seed predation of endophyte-infected (E+) and endophyte-free (E?) tall fescue (in wild grass populations and in a field experiment) and meadow fescue (Schedonorus pratensis; in a field experiment only). Endophytes were detected in only one of the 13 cultivars. In contrast, >90% of wild tall fescue plants harbored endophytes in 45 wild populations but were absent in three inland populations in Estonia. In three wild tall fescue study sites, 17%, 22%, and 56% of the seeds were preyed upon by the cocksfoot moth. Endophyte infection did not affect seed mass of tall fescue in the field experiment. However, seed predation was lower in E+ than E? grasses in the two tall fescue populations with higher predation rates. For meadow fescue, the mean number of seeds from E+ plants was higher than E? plants, but E? and E+ seeds had equal rates of predation by the moth. Our results suggest that the effects of grass endophytes on seed production and cocksfoot moth seed predation vary considerably among grass species, and the effects may depend on herbivore pressure and other environmental conditions.     

Variable effects of endophytic fungus on seedling establishment of fine fescues

Seedborne systemic endophytic fungi of grasses are thought to be plant mutualists, because they have been shown to improve their host’s resistance against biotic and abiotic stresses. The interactions in plant–endophyte associations vary from mutualistic to parasitic with environmental conditions and the genotypes of interacting species. The possible pros and cons of endophytic fungi are expected to be most evident during the seedling establishment, where host fitness is most directly affected. If this holds true, endophytes may play a focal role in local adaptation of hosts to different environments. We examined if endophyte-infected and uninfected seeds and seedlings of two native grass species, Festuca rubra and F. ovina, differ in seed germination and seedling growth rates under greenhouse conditions. The germination of F. rubra seeds was also studied in the field. This is the first time that the effects of Epichloë endophyte on seedling establishment of fine fescues from natural populations have been experimentally evaluated. Mother plant (seed family) had a marked effect on many response variables in both grass species. Length and mean biomass of tillers of endophyte-infected (E+) F. ovina seedlings were lower, but root:shoot ratios were higher than in endophyte-free (E?) seedlings. In F. rubra, the effects of the endophyte were dependent on the habitat where the seeds were collected. The E+ seeds from river banks germinated faster than E+ seeds from meadows, and E+ seedlings from the river banks produced fewer but taller and heavier tillers than the other seedlings. Our data suggest that the effects of the endophyte infection on the seedling stage of fine fescues are dependent the species of grass, host genetic background and mother plant habitat. The germination strategy and growth form of E+ red fescue seedlings from river banks may be beneficial to surviving in the harsh conditions of that habitat.     

Occurrence and Genetic Structure of the Systemic Grass Endophyte <Emphasis Type="Italic">Epichloë festucae</Emphasis> in Fine Fescue Populations

Epichloë species are systemic fungal endophytes that usually specialize in a certain group of related grass species. We examined the infection frequency of Epichloë festucae in populations of two fine fescue species (Festuca rubra and F. ovina) in natural and seminatural habitats at 86 study sites (total = 2514 plants) across Finland and northern Norway. Infection incidence varied significantly among grass species and populations. A substantial number of the F. rubra and F. ovina populations (53 out of 77 and 25 out of 30, respectively) were either endophyte-free or had very low (<20%) infection frequencies. The highest infection frequencies were found in subarctic areas. Moreover, infection incidence differed between habitats. In the area with the highest infection frequencies, we used microsatellite markers to study genetic diversity and the rates of gene flow of E. festucae among 12 F. rubra populations. Twenty out of the 25 fungal genotypes detected with four microsatellite markers were carrying multiple alleles in at least one locus, indicating multiple infections or vegetative hybridization of the fungus. One dominant genotype occurred in all 12 populations, representing 63.5% of all isolates. We found a moderate level of average genotypic variation and a low level of genetic differentiation (F _st = 0.0814). There was no correlation between infection frequency and genotypic diversity. Although the existence of a dominant genotype and the detected linkage disequilibrium suggest that the fungus is mainly asexual and vertically transmitted, the multiallelic loci and variation of genetic diversity among populations indicate occasional contagious spread and sexual or parasexual recombination of the fungus in some populations. Furthermore, the genotypes carrying multiallelic loci suggest the possibility of multiple infections or hybridization of the endophyte.     

Artificial infection of grasses with endophytes

The endophytic fungi Acremonium loliae and a Gliocladium-like sp. were isolated from Lolium perenne; A. coenophialum and a Phialophora-like sp. from Festuca arundinacea; and Epichloe typhina from F. rubra. All five fungi infected endophyte-free seedlings of the host grasses and F. arundinacea after artificial inoculation. All fungi except A. coenophialum were able to infect L. perenne. The inoculation technique involved placing endophyte mycelium into the coleoptile tissue of sterile seedlings growing on water agar in Petri dishes. Infection of mature plants with endophytes was not achieved. The presence of some endophytes in grasses can be beneficial to plant growth and persistence but deleterious to the health of animals which graze them. The desirability of infecting cultivars of grasses with endophytes is discussed.     

Widespread occurrence of Neotyphodium-like endophyte in populations of Bromus tomentellus Boiss. in Iran

Neotyphodium species occur as endophytic fungi in cool-season grasses around the world. The beneficial aspects of grass-Neotyphodium associations have provoked researchers to look for a novel association in plant species where this symbiotum has not been reported. We surveyed Russian bromegrass (Bromus tomentellus Boiss.) accessions from a germplasm collection for the presence of Neotyphodium spp. fungi and determined levels of endophyte infection in B. tomentellus populations in native rangelands of Iran. Among 50 collected accessions, symbiotic fungi were detected in 45 accessions without any symptoms of choke disease on host plants. In culture medium, fast-growing endophytes appeared from seeds after 7-14 days. Plants grown from seed collections were 80-100% infected. Based on morphological characteristics and PCR analysis, we concluded that this fungus is a member of the Neotyphodium group of endophytic fungi. Lack of apparent toxicity to grazing animals suggests a place for endophyte-infected B. tomentellus in rangeland renovation, providing this infected grass exhibits increased tolerance to abiotic stresses.     

Vertically transmitted fungal endophytes: different responses of host-parasite systems to environmental conditions

The relationship between vertically transmitted asexual fungal grass endophytes and their hosts is considered to be mutualistic. Results from agronomic field support this line of reasoning but recent studies have shown more variable results in natural systems. We investigated how high and low nutrient and water treatments affected biomass allocation patterns of endophyte‐infected and uninfected Festuca pratensis and F. rubra in greenhouse experiments over two growing seasons. Irrespective of infection status, both grass species showed improved performance on highly fertilized and watered soils. However, infected F. pratensis plants produced larger tillers than endophyte‐free plants on soil low in nutrients and water in the first growing season, although they (E+) otherwise showed decreased performance on nutrient‐poor soil. In low nutrient and water conditions, endophyte‐infected plants produced less tillers and had lower total biomass compared to uninfected plants, and displayed a negative phenotypic correlation between seed production and vegetative growth. The latter indicates costs of reproduction when the plant shares common resources with the fungal endophyte. However, endophyte infection status (E+, E?) interacted significantly with the soil fertilisation in terms of plant growth, having a stronger positive effect on growth in infected F. pratensis plants. In F. rubra, endophyte‐infected plants showed higher vegetative growth in fertilized and watered soils compared to uninfected plants. However, infected plants tended to produce fewer inflorescences. This had no effect on seed production, perhaps because seed production was partly replaced by asexual pseudovivipary. Contrary to the general assumption in the literature that fungal endophytes are plant mutualists, these findings suggest that the costs of endophytes may outweigh their benefits in resource limited conditions. However, the costs of endophyte infections appear to differ among the grass species studied; costs of endophytes were mainly detected in F. pratensis under low nutrient conditions. We propose that differences in response to endophyte infection in these species may depend on the differences in life‐history strategies and environmental requirements of these two fescue and fungal species and may change during the life span of the plant.     

Does endophyte symbiosis resist allelopathic effects of an invasive plant in degraded grassland?

Allelopathic effects and plant associated systemic endophytic fungi are often thought to play a role in the invasion of exotic plant species. Here, we tested the inhibitory effects of the aqueous extracts of the hemiparasitic weed Pedicularis kansuensis on seed germination and seedling growth of endophyte-free (E−) and -infected (E+) grass species, Stipa purpurea and Elymus tangutorum. The weed extracts significantly inhibited both seed germination and seedling growth of the target grass species. Extracts from the inflorescences gave greater inhibition than those from the stems or roots, while the concentration of the extract had a direct effect on the extent of inhibition. The E+ target plants were less susceptible to the extracts than their E-counterparts. Our results suggest that the allelopathic potential of P. kansuensis will lead to increased frequencies of endophyte infected plants in grass populations.     

Expression of a novel chitinase by the fungal endophyte in Poa ampla

Many wild and cultivated cool-season grass species are naturally infected with fungal endophytes of the genera Neotyphodium and Epichlo?. These associations generally are considered mutualistic with the plants benefiting from reduced herbivory and the fungi benefiting from nutrients supplied by the plants. The fungi secrete proteins that might have a role in the interspecies symbiosis. In the interaction between Poa ampla Merr. and the endophyte Neotyphodium sp., a fungal chitinase was detected in the apoplastic protein fraction. The chitinase was also the major protein secreted in culture. Sequence analysis of the chitinase revealed it has a low level of amino acid sequence identity to other fungal chitinases and one of the conserved active site residues is altered. DNA gel-blot analysis indicated the chitinase was encoded by a single gene. Expression of similar chitinases also was detected in endophyte-infected tall fescue (Festuca arundinacea Schreb.), perennial ryegrass (Lolium perenne L.) and Chewings fescue (Festuca rubra L. subsp. fallax [Thuill] Nyman). This is the first report of an endophyte chitinase expressed in the infected host grass. As a secreted hydrolytic enzyme, the chitinase might have roles in the nutrition, growth or defense of the endophyte.     

Forest habitat characteristics affect balance between sexual reproduction and clonal propagation of the ectomycorrhizal mushroom Hebeloma cylindrosporum

Endophytic fungi, especially asexual, systemic endophytes in grasses, are generally viewed as plant mutualists, mainly through the action of mycotoxins, such as alkaloids in infected grasses, which protect the host plant from herbivores. Most of the evidence for the defensive mutualism concept is derived from studies of agronomic grass cultivars, which may be atypical of many endophyte-host interactions. I argue that endophytes in native plants, even asexual, seed-borne ones, rarely act as defensive mutualists. In contrast to domesticated grasses where infection frequencies of highly toxic plants often approach 100%, natural grass populations are usually mosaics of uninfected and infected plants. The latter, however, usually vary enormously in alkaloid levels, from none to levels that may affect herbivores. This variation may result from diverse endophyte and host genotypic combinations that are maintained by changing selective pressures, such as competition, herbivory and abiotic factors. Other processes, such as spatial structuring of host populations and endophytes that act as reproductive parasites of their hosts, may maintain infection levels of seed-borne endophytes in natural populations, without the endophyte acting as a mutualist.     

Plant population and genotype effects override the effects of Epichloë endophyte species on growth and drought stress response of Achnatherum robustum plants in two natural grass populations

Aims In cool-season grasses, systemic and vertically transmitted Epichlo? infections often provide a suite of benefits including increased growth, reproduction and competitive abilities. However, these effects of Epichlo? endophytes on their hosts often depend upon host and endophyte genotype and environmental factors.Methods Achnatherum robustum (sleepygrass) harbors at least two Epichlo? species within natural populations in the Southwest USA. We tested the effects of endophyte infection and species, host population and plant genotype (by experimentally removing the endophyte), and soil moisture (a key limiting factor) on growth and drought stress response of infected A. robustum plants from two populations (Weed and Cloudcroft) in the Sacremento Mountains of New Mexico, USA).Important findings Although the two populations harbor distinct Epichlo? species each with very different chemoprofiles, neither endophyte status (infected vs. uninfected) nor endophyte species affected most growth parameters at 8 or 25 weeks of the experiment, except for leaf length. In high water treatment, infected plants from the Weed population had longer leaf length compared with uninfected plants. In contrast, the population of origin affected all growth parameters, including plant height, leaf number, length and width, tiller number and shoot and root biomass, as well as wilting time. Grasses from the Cloudcroft population generally showed greater growth than grasses from the Weed population. Endophyte infection did affect wilting time, with infection in the Weed population generally reducing time to wilting under low and high water, whereas infection in the Cloudcroft population reduced time to wilting only under high water conditions. Our results suggest that plant population and their associated plant genotypes may play a much larger role in endophyte–host grass interactions in varying environments than previously thought. Asexual Epichlo? species may be compatible with only specific host genotypes within populations such that the phenotypic effects due to population may be greater than phenotypic changes influenced by variation in the endophyte.     

The effect of feeding tall fescue seed infected by Acremonium coenophialum on pregnancy and parturition in female rats

1. Female Sprague-Dawley rats (Rattus norvegicus) were randomly assigned to various dietary treatments containing: (1) 100% Purina rodent chow, ad libitum; (2) same as 1, but restricted to daily intake of 7; (3) 50% rodent chow (w/w) and 50% endophyte-free tall fescue (Festuca arundinacea) seed; (4) same as 3, but restricted to intake of 5; (5) 50% rodent chow, 25% endophyte-free tall fescue seed and 25% endophyte-infected (Acremonium coenophialum) tall fescue seed; (6) 50% rodent chow, 12.5% endophyte-free and 37.5% endophyte-infected tall fescue seed; and (7) 50% rodent chow and 50% endophyte infected tall fescue seed. 2. Average daily feed intakes and average daily weight gains decreased with higher levels of endophyte infected seed. 3. Frequency of litter production was affected by all endophyte-infected containing diets. 4. Conception was reduced only in dietary treatment (7). 5. Litter weights, number of pups per litter and weight per pup were proportionally reduced as higher levels of infected seed were incorporated in the ingested diets.     

禾草-内生真菌共生体在草地农业系统中的作用

综述了国内外近年对禾草 -内生真菌 (N eotyphodium)的研究进展。全世界现已报道 14种禾草内生真菌 ,与 2 3个属的禾草形成共生体 ,我国已在 13属 2 5种天然草地禾草中发现内生真菌 ,其中发草属 (Descampsia)、大麦属 (H ord eum)和赖草属(L eymus)以往在国际文献中未曾报道。内生真菌在禾草体内产生的生物碱 ,致使采食带菌禾草的马、牛、羊、鹿等家畜产生中毒症状 ,每年给美国、新西兰等国造成的经济损失达 6.4亿美元之多 ,对其毒理研究取得了进展。已发现我国醉马草 (Achnatheruminebrians)对家畜的毒性与内生真菌的侵染有关。内生真菌侵染增加可使禾草对 42种害虫的抗性 ,并可增加对某些线虫和病害的抗性。与不带菌禾草相比 ,带菌禾草的另一特点是抗逆性强 ,牧草产量高。国际在该领域的研究主要集中在多年生黑麦草(L olium p erenne)和高羊茅 (Festuca arundinacea)。我国的研究发现 ,带菌布顿大麦草 (H ordeum bodg anii)和圆柱披碱草(Elymus cylind ricus)的牧草产量分别增加 3 3 .3 %和 2 78.8% ,分孽数分别增加 13 6.8%和 84.5%。目前 ,国际研究的重点包括大规模开展内生真菌生物学与生态学特性的研究 ,创造不含对家畜有害毒素的有益禾草 -内生真菌共生体 ,培育带内生真菌的草坪草品种 ,培育抗毒     

Importance of host plant species, Neotyphodium endophyte isolate, and alkaloids on feeding by Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae

Three grass host species--tall fescue, Festuca arundinacea Schreber; meadow fescue, Festuca pratensis Hudson; and perennial ryegrass, Lolium perenne L.--each infected with a number of different Neotyphodium endophyte isolates, were investigated for their effects on fall armyworm, Spodoptera frugiperda (J.E. Smith). Alkaloid profiles varied among associations. Choice and no-choice tests comparing feeding and early development of S. frugiperda larvae on endophyte-infected and endophyte-free leaf blade material were performed. Endophyte-mediated resistance to S. frugiperda was greatest in meadow fescue and weakest in tall fescue. Some endophyte isolates, particularly in perennial ryegrass and meadow fescue, had a major effect on feeding and development of S. frugiperda, whereas others had no effect or were only weakly efficacious. In tall fescue, some associations deterred S. frugiperda from feeding in choice tests but had no effect on development, whereas larvae reared on other associations weighed significantly more than control larvae fed endophyte-free grass. It was concluded that the deleterious consequences of endophyte infection were easily masked by other factors in tall fescue. Relative leaf age had no effect on feeding preferences in the three host species. Chemical analysis of herbage from the plants used, and results from a no-choice study using spiked artificial diets, failed to individually implicate any of the major known alkaloids (peramine, lolitrem B, ergovaline, and lolines) in the observed effects on S. frugiperda. Hypotheses explaining these observations, and their impact on creating desirable grass-endophyte associations for use in pastures, are discussed.     

Effect of endophytic fungi on cadmium tolerance and bioaccumulation by Festuca arundinacea and Festuca pratensis

Endophytic fungi are a group of fungi that live asymptomatically inside plant tissue. These fungi may increase host plant tolerance to biotic and abiotic stresses. The effect of Neotyphodium endophytes in two grass species (Festuca arundinacea and Festuca pratensis) on cadmium (Cd) tolerance, accumulation and translocation has been our main objective. The plants were grown in a hydroponic system under different Cd concentrations (0, 5, 10, and 20 mg L(-1)) for 6 weeks. They were also grown in soil spiked with different concentrations of Cd (0, 10, 20, and 40 mg kg(-1)) for 2 months. The results from all Cd treatments showed higher biomass production (12-24%) and higher potential to accumulate Cd in roots (6-16%) and shoots (6-20%) of endophyte-infected plants than endophyte-free plants. Cadmium accumulation by plants indicated that the grasses were capable of Cd hyperaccumulation, a property that was augmented after endophyte infection. Maximum photochemical efficiency of photosystem II (Fv/Fm) revealed that Cd stress was significantly reduced in endophyte-infected plants compared to non-infected ones.     

Effects of the Epichloë fungal endophyte symbiosis with Schedonorus pratensis on host grass invasiveness

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 high‐ or low‐endophyte infection rate were broadcast seeded into 2 × 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.     

Benefits of a fungal endophyte in Elymus virginicus decline under drought stress

In most natural systems, it remains unclear whether microbial symbionts can help plants adapt to rapidly changing environments. Here, we tested the hypothesis that fungal endophyte symbiosis in a widespread, native grass species, Elymus virginicus, would promote host tolerance of drought. In a growth chamber experiment, we manipulated water availability to plants naturally infected with the endophyte Epichloë elymi and to plants that were experimentally disinfected. The drought treatment imposed a ～67% reduction in water, corresponding to the very high end of drought predictions for the Midwestern US, where E. virginicus is common. In contrast to expectations, E. virginicus benefited more from the endophyte under daily watering than under drought. Disinfected plants had 45% less aboveground biomass than naturally infected plants under daily watering and only 23% less under drought. Both the number of tillers produced and root biomass were reduced by disinfection, with a greater difference between endophyte treatments under daily watering than under drought. There were no effects of either the endophyte or drought on aphid colonization of the plants. To put these results into a broader geographic context, we surveyed endophyte infection frequencies across 43 populations, including wild populations, commercial stock and germplasm resources. Endophyte frequencies varied from 0% to 100%, and frequencies were much higher for wild populations than germplasm resources. Natural variation in endophyte frequencies combined with the heritable transmission of endophytes from plants to seeds provides opportunities for climate change to affect selection on the maintenance of endophyte symbiosis in E. virginicus.     

Does An Asexual Endophyte Symbiont Alter Life Stage and Long-Term Survival in a Perennial Host Grass?

Asexual, seedborne endophytic fungi in perennial grasses are often viewed as strong mutualists because fitness of the symbiont and host grass are closely coupled. However, at least for some native grasses, the asexual endophyte, Neotyphodium, acts parasitically, yet remains at high frequencies in natural populations. Most previous studies of Neotyphodium effects on host survival have been short term relative to the long life span of the perennial grass host. We therefore tested the hypothesis that Neotyphodium alters the survival in various life stages and long-term survival of adult native Arizona fescue (Festuca arizonica). To test the former, we planted 40 infected (E+) and 40 uninfected (E−, endophyte removed) seeds from four different maternal plants in the field under ambient conditions. We followed survival of seeds, seedlings, and adult plants over a 5-year period. To test the latter, we determined the infection of 1633 adult plants and followed their survival over the next 5–7 years. E+ seeds did not differ from uninfected seeds in terms of overall survival from seed germination to seedling to adult. However, the shape of the survival curve differed, with E+ plants showing higher mortality in early life stages. E+ adult plants did not differ from E− plants in long-term survival. Survival was generally very high during the study, which included a severe and prolonged drought. Infection by asexual Neotyphodium does not increase survival in early life stages or that of adult plants. Because asexual, vertically transmitted symbionts are predicted by evolutionary theory to be strong mutualists, the persistence of high infection frequencies in natural populations without long-term benefits to the host remains enigmatic. One possible explanation is that the long life span of the perennial host and low seedling recruitment may obscure either the costs or benefits of endophyte infection.     

Fungal endosymbionts affect aphid population size by reduction of adult life span and fecundity

The symbiosis between grasses and endophytic fungi is a common phenomenon and can affect herbivore performance through acquired, chemical plant defence by fungal alkaloids. In laboratory experiments, two species of common grass aphids, Rhopalosiphum padi and Metopolophium dirhodum were tested, in a population experiment (on four plant cultivars) and individually (on one plant cultivar) for the effects of the endophyte, Neotyphodium lolii, that forms symbiotic associations with perennial ryegrass Lolium perenne. In the population experiment that lasted for four aphid generations both aphid species showed decreased population sizes when feeding on each of the four endophyte-infected cultivars. Individuals of R. padi tested individually showed reduced adult life span and fecundity when feeding on infected plants. Individuals of M. dirhodum showed no response in any of the traits measured. This suggests that R. padi individuals are more sensitive to endophyte infection than M. dirhodum individuals. However, all infected grass cultivars reduced population sizes of both aphid species over four generations. Therefore, fungal endophytes can reduce populations of aphid herbivores independent of plant cultivars.     

Dynamics of Neotyphodium endophyte infection in ageing seed pools: incidence of differential viability loss of endophyte,infected seed and non-infected seed

Symbiotic associations between grasses and vertically transmitted endophytic fungi are widespread in nature. Within grass populations, changes in the frequency of infected plants are driven by influence of the endophyte on the fitness of their hosts and by the efficiency of endophyte transmission from parent plants to their offspring. During the seed stage, the endophyte might influence the fitness of its host by affecting the rate of seed viability loss, whereas the efficiency of endophyte transmission is affected by losses of viability of the fungus within viable seeds. We assessed the viability losses of Lolium multiflorum seeds with high and low level of infection of the endophyte Neotyphodium occultans, as well as the loss of viability of the fungus itself, under accelerated seed ageing and under field conditions. Starting with high endophyte-infected accessions of L. multiflorum, we produced their low endophyte-infected counterparts by treating seeds with a fungicide, and subsequently multiplying seeds in adjacent plots allowing pollen exchange. In our accelerated ageing experiments, which included three accessions, high endophyte-infected seeds lost viability significantly faster than their low endophyte-infected counterpart, for only one accession. High endophyte-infected seeds of this particular accession absorbed more water than low endophyte-infected seeds. In contrast, the endophyte lost viability within live seeds of all three accessions, as the proportions of viable seeds producing infected seedlings decreased over time. In our field experiment, which included only one accession, high endophyte-infected seed lost viability significantly but only slightly faster than low endophyte-infected seed. In contrast, the loss of viability of the endophyte was substantial as the proportions of viable seeds producing infected seedlings decreased greatly over time. Moving the seeds from the air to the soil surface (simulating seed dispersion off the spikes) decreased substantially the rate of seed viability loss, but increased the rate of endophyte viability loss. Our experiments suggest that, in ageing seed pools, endophyte viability loss and differential seed mortality determine decreases in the proportions of endophyte-infected seeds in L. multiflorum. Endophyte viability loss within live seeds contributes substantially more to infection frequency changes than differential viability losses of infected and non-infected seeds.     

Grass-herbivore interactions altered by strains of a native endophyte

Many plants support symbiotic microbes, such as endophytic fungi, that can alter interactions with herbivores. Most endophyte research has focused on agronomically important species, with less known about the ecological roles of native endophytes in native plants. In particular, whether genetic variation among endophyte symbionts affects herbivores of plant hosts remains unresolved for most native endophytes. Here, we investigate the importance of native isolates of the endophyte Epichlo? elymi in affecting herbivory of the native grass host, Elymus hystrix. Experimental fungal isolate-plant genotype combinations and endophyte-free control plants were grown in a common garden and exposed to natural arthropod herbivory. Fungal isolates differed in their effects on two types of herbivory, chewing and scraping. Isolates exhibiting greater sexual reproduction were associated with greater herbivore damage than primarily asexual isolates. Endophyte infection also altered patterns of herbivory within plants, with stroma-bearing tillers experiencing up to 30% greater damage than nonstroma-bearing tillers. Results suggest that intraspecific genetic variation in endophytes, like plant genetic variation, can have important 'bottom-up' effects on herbivores in native systems.