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     

Genetic Compatibility Determines Endophyte-Grass Combinations

Even highly mutually beneficial microbial-plant interactions, such as mycorrhizal- and rhizobial-plant exchanges, involve selfishness, cheating and power-struggles between the partners, which depending on prevailing selective pressures, lead to a continuum of interactions from antagonistic to mutualistic. Using manipulated grass-endophyte combinations in a five year common garden experiment, we show that grass genotypes and genetic mismatches constrain genetic combinations between the vertically (via host seeds) transmitted endophytes and the out-crossing host, thereby reducing infections in established grass populations. Infections were lost in both grass tillers and seedlings in F₁ and F₂ generations, respectively. Experimental plants were collected as seeds from two different environments, i.e., meadows and nearby riverbanks. Endophyte-related benefits to the host included an increased number of inflorescences, but only in meadow plants and not until the last growing season of the experiment. Our results illustrate the importance of genetic host specificity and trans-generational maternal effects on the genetic structure of a host population, which act as destabilizing forces in endophyte-grass symbioses. We propose that (1) genetic mismatches may act as a buffering mechanism against highly competitive endophyte-grass genotype combinations threatening the biodiversity of grassland communities and (2) these mismatches should be acknowledged, particularly in breeding programmes aimed at harnessing systemic and heritable endophytes to improve the agriculturally valuable characteristics of cultivars.     

Endophyte-grass-herbivore interactions: the case of Neotyphodium endophytes in Arizona fescue populations

Neotyphodium endophytes in introduced agronomic grasses are well known to increase resistance to herbivores, but little is known of interactions between Neotyphodium endophytes and herbivores in native grass populations. We investigated whether endophytes mediate plant-herbivore interactions in a native grass species, Festuca arizonica in the southwestern United States, in two ways. First, to test the prediction that the presence and frequency of endophyte-infected (E+) plants should increase with increasing herbivory, we determined endophyte frequencies over a 4-year period in six natural Arizona fescue populations. We compared Neotyphodium frequency among plants growing inside and outside long-term vertebrate grazing exclosures. Second, we experimentally tested the effects of Neotyphodium infection, plant clone, and soil nutrients on plant resistance to the native grasshopper Xanthippus corallipes. Contrary to predictions based upon the hypothesis that endophytes increase herbivore resistance, levels of infection did not increase in plants subjected to grazing outside of exclosures relative to ungrazed plants within exclosures. Instead, endophyte frequencies tended to be greater inside the exclosures, where long-term vertebrate grazing was reduced. The grasshopper bioassay experiment corroborated these long-term patterns. Survival of grasshoppers did not differ between infected (E+) and uninfected (E–) plants. Instead, mean relative growth rate of grasshoppers was higher on E+ grasses than on E– ones. Growth performance of newly hatched grasshopper nymphs varied among host plant clones, although two of six clones accounted for most of this variation. Our results suggest that Neotyphodium-grass-herbivore interactions may be much more variable in natural communities than predicted by studies of agronomically important Neotyphodium-grass associations, and herbivory is not always the driving selective force in endophyte-grass ecology and evolution. Thus, alternative hypotheses are necessary to explain the wide distribution and variable frequencies of endophytes in natural plant populations. Received: 15 February 1999 / Accepted: 19 July 1999     

Genetic diversity in epichloid endophytes of Hordelymus europaeus suggests repeated host jumps and interspecific hybridizations

Epichloid fungal endophytes (Epichloë and Neotyphodium spp.) are excellent model systems for studying speciation processes because of their variable life history traits that are linked to host grass fitness. Presumed jumps to new hosts and subsequent somatic hybridizations appear to be common among epichloid endophytes resulting in increased genetic variation upon which selection can act and speciation be initiated. In this study, we explored the endophyte diversity of a rare European native woodland grass species, Hordelymus europaeus, along a latitudinal transect covering the entire distribution range of H. europaeus. From 28 populations in six countries, isolates were sampled and molecularly characterized. Based on the sequences of tubB and tefA, six distinct epichloid taxa (interspecific hybrid or cryptic haploid species) were found, of which four were novel and two have been previously reported from this host. Of the novel endophytes, two were presumed to be interspecific hybrids and two of nonhybrid origin. While previously known endophytes of H. europaeus are seed‐born and strictly asexual, one of the novel nonhybrid endophytes found in the glacial refugium of the Apennine peninsula reproduced sexually in cultured plants. This is the first case of a seed‐borne, but sexually reproducing endophyte of this host. We discuss the origin, and possible ancestral species, of the six epichloid taxa using phylogenetic analyses. Repeated host jumps and somatic hybridizations characterize the diversity of the endophytes. To date, no other grass species is known to host a larger diversity of endophytes than H. europaeus.     

Stroma-forming endophyte Epichloë glyceriae provides wound-inducible herbivore resistance to its grass host

Fungal endophyte-grass associations are diverse and complex. Some endophytes (e.g. Neotyphodium spp.) reproduce asexually by growing vegetatively into host seeds and many of these vertically-transmitted endophytes form mutualisms with their hosts by providing high levels of alkaloids, such as lolines, that reduce herbivore performance. Additionally, Neotyphodium coenophialum provides wound-inducible herbivore resistance through increased production of lolines. Neotyphodium likely evolved from Epichloë spp. which are sexually reproducing endophytes that are transmitted horizontally to the next host generation through production of stromata (fruiting bodies), which sterilize host grasses. We asked if wound-inducible resistance like that in N . coenophialum also occurs in the ancestral, sexually reproducing Epichloë glyceriae , which infects Glyceria striata . Host grasses were damaged by fall armyworm caterpillars, artificially cut, or left undamaged. An aphid bioassay tested the plant's toxicity to herbivores, expression of lolc (a gene in the loline biosynthesis pathway) was quantified using real-time RT-PCR, and loline concentration was quantified using gas chromatography and mass spectrometry. Artificially-damaged plants supported fewer live aphids, had greater lolc mRNA expression, and greater loline concentration than undamaged plants. Herbivore-damaged plants supported intermediate performance by aphids, low lolc mRNA expression, and minimal loline concentration. Our study is the first to demonstrate sexual endophytes can produce lolines following wounding. This suggests wound-induced responses are ancestral within the Epichloë / Neotyphodium clade and reveals a trait of grass endophytes that may have predisposed them for the evolution of defensive mutualisms with their hosts.     

An endophyte‐rich diet increases ant predation on a specialist herbivorous insect

1. All plants form symbioses with microfungi, known as endophytes, which live within plant tissues. Numerous studies have documented endophyte–herbivore antagonism in grass systems, but plant–endophyte–insect interactions are highly variable for forbs and woody plants. 2. The net effect of endophytes on insect herbivory may be modified by their interactions with higher trophic levels, such as predators. Including these multitrophic dynamics may explain some of the variability among endophyte studies of non‐grass plants, which are currently based exclusively on bitrophic studies. 3. The abundance of natural foliar endophytes in a Neotropical vine was manipulated and beetles were fed high or low endophyte diets. Experimental assays assessed whether dietary endophyte load affected beetle growth, leaf consumption, and susceptibility to ant predation. 4. Beetles feeding on high‐ versus low‐endophyte plants had almost identical growth and leaf consumption rates. 5. In a field bioassay, however, it was discovered that feeding on an endophyte‐rich diet increased a beetle's odds of capture by predatory ants nine‐fold. 6. Endophytes could thus provide an indirect, enemy‐mediated form of plant defence that operates even against specialist herbivores. We argue that a multitrophic approach is necessary to untangle the potentially diverse types of endophyte defence among plants.     

禾草内生真菌对其它微生物的影响研究进展

禾草内生真菌在宿主植物的茎叶等地上组织中普遍存在,不仅能够提高禾草对生物与非生物逆境的抗性,而且能够对周围环境中的不同微生物类群产生影响。主要总结了禾草Neotyphodium/Epichlo内生真菌对病原真菌、丛枝菌根真菌和土壤微生物的影响及其作用机理。发现禾草内生真菌普遍存在对病原真菌的抑制作用,而对丛枝菌根真菌存在不对称的竞争作用,且因种类而异。禾草内生真菌对土壤微生物群落的作用则会随着土壤类型和时间等外界因素发生变化。禾草内生真菌对不同类群微生物的影响机制主要包括:通过生态位竞争、抑菌物质分泌、诱导抗病性等对病原真菌造成影响;通过根系化学物质释放、营养元素调节、侵染条件差异等对丛枝菌根真菌造成影响;通过根际沉积物和凋落物等对土壤微生物群落造成影响。禾草内生真菌产生的生物碱能提高宿主植物对包括昆虫在内草食动物采食的抗性,影响病原菌的侵入、定殖和扩展;根组织分泌物中包含次生代谢产物能够抑制菌根真菌、土传病原真菌及其它土壤微生物的侵染与群落组成;也可能通过次生代谢物影响禾草的其它抗性。因此,禾草内生真菌在植物-微生物系统中的作用应该给予更多的关注和深入研究。     

Effects of grassland management,endophytic fungi and predators on aphid abundance in two distinct regions

Aims Fungal endophytes of cool-season grass species produce alkaloids toxic to herbivores, affecting food webs in agricultural and natural ecosystems. Field studies about the effects of endophytes on herbivores are rare and show contradictory results, leading to uncertain conclusions about the nature of endophyte–grass symbiosis. We asked whether the environmental contexts of local and regional scales and predation could modify the effects of endophytes on herbivores.Methods In a full factorial field experiment, we quantified the abundance of the aphid species Rhopalosiphum padi on the potted host grass Lolium perenne, which was either infected or uninfected with the endophytic fungus Neotyphodium lolii. Predators were either excluded or had free access to the pots with the aphids. One hundred and sixty grass pots were located in two regions on altogether 40 grassland sites, half of the sites intensively and half extensively managed. We tested the importance of endophyte infection, study region, management intensity of grasslands, predation and all two-way interactions on aphid abundance.Important findings Endophyte infection reduced aphid abundance significantly in one study region only. In both regions, we found that the impacts of aphidophagous predators and grassland management intensity on aphid abundance were substantially stronger and more consistent than that of endophytes on aphid abundance. Pots excluding predators and pots placed on extensive grasslands contained higher aphid abundance. The impact of predators and management on aphid abundance were not modified by the endophyte. We conclude that the effect of endophytes on herbivores can be weak in field experiments and depends on environmental context at a regional scale. Hence, more field research efforts are necessary to detect the relative importance of endophytes and the environmental context on biotic interactions in ecosystems.     

Role of Diverse Non-Systemic Fungal Endophytes in Plant Performance and Response to Stress: Progress and Approaches

Plant–fungal symbiotic associations are ubiquitously distributed in natural plant communities. Besides the well-studied mycorrhizal symbiosis and grass systemic clavicipitaceous endophytes, recently, nonsystemic and horizontally transmitted fungal endophytes serving as plant symbionts have been increasingly recognized. Pure culture isolation and culture-independent molecular methods indicate that all parts of healthy plant tissues potentially harbor diverse and previously unknown fungal lineages. Limited evidence also supports a hypothesis that endophytic mycobiota dynamics may have a role in evolution of plants. High variability or “balanced antagonism” can be generally characterized with host–endophyte interactions, which implies that the outcome of symbiotic interactions can fall within a continuum ranging from mutualism to commensalism, and ultimately pathogenicity. Despite this complicated system, admittedly, fungal endophytes really endow the host with an extended phenotype. Accumulating facts illustrate that plant nutrition acquisition, metabolism, and stress tolerance may be strengthened or modulated via fungal symbionts. Piriformospora indica, a member of the order Sebacinales, simultaneously confers host resistance to biotic and abiotic stress. The ecological relevance of other fungal groups, including foliar endophytes, root dark septate endophytes (DSEs), some opportunistic and avirulent microsymbionts (for example, Trichoderma and Fusarium), and even uncultured fungi structurally and physiologically integrated with host tissues, are also being deeply exploited. Production of bioactive metabolites by fungi, overexpression of stress-related enzymes, and induced resistance in hosts upon fungal colonization are responsible for direct or indirect beneficial effects to hosts. More knowledge of endophyte-mediated enhancement of host performance and fitness will offer alternatively valuable strategies for plant cultivation and breeding. Meanwhile, with unprecedented loss of biodiversity, discovery of indigenously novel symbiotic endophytes from natural habitats is urgently needed. In addition, we present some approaches and suggestions for studying host–endophyte interactions.     

内生真菌对草坪植物病原真菌抑制作用的比较

分别从野生牧草羽茅(Achnatherum sibiricum (L.) Keng)、栽培种高羊茅(Festuca arundinacea Schreb.)(品种Millennium)、栽培种黑麦草(Lolium perenne L.) (品种Justus)中分离出内生真菌Neotyphodium sp.、N. coenophialum和N. lolli,通过体外培养法比较了这3种内生真菌对草坪植物病原真菌的抑制作用.结果表明,从羽茅中分离的内生真菌Neotyphodium sp.在两菌相交前对所有供试的病原真菌都有一定的抑制作用,其中对枝孢霉属(Cladosporium sp.)、弯孢霉属(Curvularia sp.)和拟茎点属(Phomopsis sp.)病原真菌的抑制效果尤为显著,对峙培养3d后的抑菌率分别达70.1%、52.3%和30.9%,营养竞争作用、重寄生作用是其主要的拮抗机制;从高羊茅中分离的内生真菌N. coenophialum对枝孢霉属病原真菌存在一定的抑制作用;而从黑麦草中分离的内生真菌N. lolli与病原真菌对峙培养时,病原真菌菌落慢慢侵占整个营养空间,内生真菌停止生长并逐渐褐变死亡.体外培养结果说明Neotyphodium sp.对供试病原真菌的拮抗效果优于N. coenophialum和N. lolli,由此推测Neotyphodium sp.与宿主植物羽茅的共生可能有利于宿主植物抵抗病原真菌的侵扰.     

Detection and quantification of three distinct Neotyphodium lolii endophytes in Lolium perenne by real time PCR of secondary metabolite genes

Perennial ryegrass (Lolium perenne) is a widely used pasture grass, which is frequently infected by Neotyphodium lolii endophytes that enhance grass performance but can produce alkaloids inducing toxicosis in livestock. Several selected endophyte strains with reduced livestock toxicity, but that confer insect resistance, are now in common use. Little is known regarding the survival and persistence of these endophytes when in competition with common toxic endophytes. This is mainly because there are currently no assays available to easily and reliably quantify different endophytes in pastures or in batches of seeds infected with multiple strains. We developed real time PCR assays, based on secondary metabolite genes known to differ between N. lolii endophyte strains, to quantify two selected endophytes, AR1 and AR37, and a common toxic ecotype used in New Zealand. A duplex PCR allowed assessment of endophyte:grass DNA ratios with high sensitivity, specificity and precision. Endophyte specific primers/probes could detect contamination of AR37 seeds with other endophytes down to a level of 3–25%. We demonstrated that it is possible to quantify different endophyte strains simultaneously using multiplex PCR. This method has potential applications in management of endophytes in pastures and in fundamental research into this important plant-microbe symbiosis.     

Interactions among fungal endophytes,grasses and herbivores

The interaction between two species often depends on the presence or absence of a third species. One widespread three-species interaction involves fungal endophytes infecting grasses and the herbivores that feed upon them. The endophytes are allied with the fungal family Clavicipitaceae and grow systemically in intercellular spaces in above-ground plant tissues including seeds. Like relatedClaviceps species, the endophytes produce a variety of alkaloids that make the host plants toxic or distasteful to herbivores. A large number of grass species are infected, especially cool-season grasses in temperate areas. Field and laboratory studies have shown that herbivores avoid infected plants in choice trials and suffer increased mortality and decreased growth on infected grasses in feeding experiments. Resistance to herbivores may provide a selective advantage to infected plants in competitive interactions with noninfected plants. Recent studies have shown that differential herbivory can reverse competitive hierarchies among plant species. Both endophyte-infected and noninfected tall fescue grass (Festuca arundinacea) are outcompeted by orchardgrass (Dactylis glomerata) in the absence of insect herbivory. However, when herbivores are present infected tall fescue outcompetes orchardgrass. These results suggest that the frequency of infection in grass species and grassland communities will increase over time. Several studies are reviewed illustrating increases in infection frequency within grass populations subject to herbivore pressure. Endophytic fungi may be important regulators of plant-herbivore interactions and so indirectly affect the structure and dynamics of plant communities.     

Interactions of arboreal yeast endophytes: an unexplored discipline

The value of healthy forest ecosystems is well known and trees in these systems form symbioses with a variety of living organisms. This review focuses on literature pertaining to the potential interactions of arboreal yeast endophytes with trees and their associated insects. Although very little is known about the symbioses of arboreal yeast endophytes, indications are that some of these unicellular fungi produce plant-growth promoting phytohormones, while others are antagonistic towards phytopathogens or are capable of producing pheromones that affect the behavior of insect herbivores. However, more research needs to be conducted to fully understand the role of arboreal yeast endophytes in ecosystem processes.     

An ecological framework for understanding the roles of Epichloë endophytes on plant defenses against fungal diseases

Plants harbor a wide diversity of microorganisms in their tissues. Some of them have a long co-evolutionary history with their hosts, likely playing a pivotal role in regulating the plant interaction with other microbes such as pathogens. Some cool-season grasses are symbiotic with Epichloë fungal endophytes that grow symptomless and systemically in aboveground tissues. Among the many benefits that have been ascribed to endophytes, their role in mediating plant interactions with pathogens has been scarcely developed. Here, we explored the effects of Epichloë fungal endophytes on the interaction of host grasses with fungal pathogens. We made a meta-analysis that covered a total of 18 host grass species, 11 fungal endophyte species, and 22 fungal pathogen species. We observed endophyte-mediated negative effects on pathogens in vitro and in planta. Endophyte negative effects on pathogens were apparent not only in laboratory but also in greenhouse and field experiments. Epichloë fungal endophytes had negative effects on pathogen growth and spores' germination. On living plants, endophytes reduced both severity and incidence of the disease as well as colonization and subsequent infection of seeds. Symbiosis with endophytes showed an inhibitory effect on debilitator and killer pathogens, but not on castrators, and this effect did not differ among biotrophic or necrotrophic lifestyles. We found that this protection can be direct through the production of fungistatic compounds, the competition for a common resource, or the induction of plant defenses, and indirect associated with endophyte-generated changes in the abiotic or the biotic environment. Several mechanisms operate simultaneously and contribute differentially to the reduction of disease within grass populations.     

Fungal endophytes: common host plant symbionts but uncommon mutualists

Fungal endophytes are extremely common and highly diverse microorganismsthat live within plant tissues, but usually remain asymptomatic.Endophytes traditionally have been considered plant mutualists,mainly by reducing herbivory via production of mycotoxins, suchas alkaloids. However, the vast majority of endophytes, especiallyhorizontally-transmitted ones commonly found in woody plants,apparently have little or no effect on herbivores. For the systemic,vertically-transmitted endophytes of grasses, mutualistic interactionsvia increased resistance to herbivores and pathogens are morecommon, as predicted by evolutionary theory. However, even inthese obligate symbioses, endophytes are often neutral or evenpathogenic to the host grass, depending on endophyte and plantgenotype and environmental conditions. We present a graphical model based upon variation in nitrogenflux in the host plant. Nitrogen is a common currency in endophyte/hostand plant/herbivore interactions in terms of limitations tohost plant growth, enhanced uptake by endophytes, demand forsynthesis of nitrogen-rich alkaloids, and herbivore preferenceand performance. Our graphical model predicts that low alkaloid-producingendophytes should persist in populations when soil nutrientsand herbivory are low. Alternatively, high alkaloid endophytesare favored under increasing herbivory and increasing soil nitrogen,at least to some point. At very high soil nitrogen levels, uninfectedplants may be favored over either type of infected plants. Thesepredictions are supported by patterns of infection and alkaloidproduction in nature, as well by a manipulative field experiment.However, plant genotype and other environmental factors, suchas available water, interact with the presence of the endophyteto influence host plant performance.     

Symbiosis between grasses and asexual fungal endophytes

The symbiosis between vertically transmitted asexual endophytic fungi and grasses is common and generally considered to be mutualistic. Recent studies have accumulated evidence of negative effects of endophytes on plant fitness, prompting a debate on the true nature of the symbiosis. Genetic factors in each of the two partners show high variability and have a range of effects (from positive to negative) on plant fitness. In addition, interacting environmental factors might modify the nature of the symbiosis. Finally, competition and multitrophic interactions among grass consumers are influenced by endophytes, and the effects of plant neighbours or consumers could feedback to affect plant fitness. We propose a mutualism-parasitism continuum for the symbiosis between asexual endophytes and grasses, which is similar to the associations between plants and mycorrhizal fungi.     

Broad-scale geographic patterns in the distribution of vertically-transmitted, asexual endophytes in four naturally-occurring grasses in Sweden

The presence and distribution of vertically-transmitted, asexual Neotyphodium/Epichloë endophytes in four species of widely distributed grasses, all members of the sub-family Pooideae, were determined at 57 spatially-distinct sites across Sweden in naturally-occurring grass populations. While these endophytes are well-studied in agricultural systems, much less is known about their abundance and distribution in non-agricultural systems at larger scales across landscapes. We used two screening methods to detect endophytes: 1) visual inspection of fixed, stained grass shoots, and 2) immunoblot cards with monoclonal antibodies specific for Neotyphodium / Epichloë endophytes. Infection frequency (i.e. the proportion of individuals) varied widely among species and among sites, a finding common to most studies performed in non-agricultural ecosystems. Festuca rubra had the highest overall infection frequency (23% visual screening, 27% immunoblot screening), while Deschampsia flexuosa (4%) and Poa trivialis (4%) had low frequencies of infection. None of the sampled Agrostis capillaris populations were infected. In F. rubra , the within-site infection frequency varied from 0 to 100%. A significant altitudinal gradient was found for F. rubra , with the infection frequency of the vertically-transmitted endophyte Epichloë festucae decreasing with increasing altitude above sea level. The high variation across and within grass species at different geographical locations that ours and others' studies reveal, agree with suggestions that agronomic model systems cannot be readily extrapolated to understand the ecological role of endophytes in native grasses in the wild. Further investigation into the underlying cause of the observed altitudinal gradient is required to understand broader-scale patterns in the distribution of endophyte-infected grasses.     

Epichloë endophytes: fungal symbionts of grasses

Recent developments have increased our understanding of the evolution of mutualistic associations between Epichlo? endophytes and their grass hosts. Most of the asexual species appear to be interspecific hybrids. Although endophytes form compatible associations with their natural hosts, transfers to other hosts elicit a range of incompatible reactions. Recently, the genes involved in the synthesis of the secondary metabolites ergot alkaloids and indole-diterpenes, which confer protective benefits on the association, have been cloned.     

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.     

禾本科植物内生真菌资源及其物种多样性

植物内生真菌是当代微生物资源研究的一个热门话题,对禾本科植物内生真菌资源研究进行了总结。与冷季型禾本科植物共生的麦角菌科epichlo内生真菌是目前的研究重点,包括偶尔在宿主植物体表形成子座的Epichlo属真菌和几乎完全不形成症状的Neotyphodium属真菌。具体介绍该真菌类群的物种多样性及其地理分布多样性,概括了它们在全球各大区域的分布特征。对近年来中国迅速发展的epichlo内生真菌的研究作了总结,最后展望了国际国内epichlo内生真菌资源探索的发展方向。特别指出:冷季型禾本科植物内生真菌在南美洲和亚洲,暖季型禾本科植物内生真菌在热带亚热带地区的研究还相对薄弱,值得今后继续加强探索和挖掘。