The interaction of a Botanophila fly species with an exotic Epichloë fungus in a cultivated grass: fungivore or mutualist?

Epichloë spp. (Ascomycetes: Clavicipitaceae) are endophytic fungii of Pooid grasses that cause choke disease, the suppression of seed production. They also host Botanophila spp. (Diptera: Anthomyiidae), the larvae of which feed on the fungus. Studies on Epichloë elymi on wild grasses indicate that the flies transfer spermatia between Epichloë mating types, thereby affecting cross‐fertilization, suggesting that the fungus–fly interaction reflects obligatory mutualism. Epichloë typhina, inadvertently introduced into western USA, was first detected in cultivated Dactylis glomerata L. fields in 1996. It spread rapidly, raising concerns about impacts on seed production. The present study was conducted to address questions pertaining to the occurrence and nature of the fungus–fly interaction in the new habitat of E. typhina. The first report of an endemic Botanophila species associated with E. typhina in Oregon is presented here. Surveys of D. glomerata fields indicated no correlation between fly abundance and fungal fertilization. In one field, no fly eggs or larvae were detected, but fertilized stromata were universally present. The fly was established in the remaining 12 fields surveyed, but while the number of stromata with fly larvae ranged from 6 to 98%, stromata development was uniform. Up to 10 larvae were present on a stroma, and these consumed >90% of the perithecia. Comparisons of pupal weights indicated that the fungal resource was not limiting, even at high larval densities. An exclusion study in a D. glomerata field also indicated that E. typhina fertilization occurred without the fly. In Oregon, the fly clearly benefits from the association with the fungus, but there is no evidence of benefit to the fungus. Thus if obligatory mutualism in the fungus–fly relationship described from the midwestern USA is the norm, our studies suggest a shift in the interaction to one of simple foraging on the fungus by fly larvae.     

A test of host specialization by insect vectors as a mechanism for reproductive isolation among entomophilous fungal species

Epichloë species are self incompatible (heterothallic) fungi that must be fertilized by spermatia from individuals of opposite mating type for successful sexual reproduction to occur. Female flies of the genus Botanophila act as vectors of the fungi by ingesting and defecating spermatia (gametes) onto fungal stromata (fruiting bodies) after oviposition. Larvae feed and develop on the stromata and thus maintain a symbiotic relationship with Epichloë fungi. We hypothesized that sole dependence on fertilized stromata as a food source would promote specialization by flies to single compatible host species and that this specialization would promote reproductive isolation among Epichloë species. Analysis of progeny of ascospores from experimental field plots in Zurich, Switzerland, indicated prevalence of specific matings between stromata of the same host, and thus was consistent with the hypothesis that flies are species-specific in their visitation behaviour. Genetic analyses of spermatia contained in the faeces of individual flies also gave some support for this hypothesis. We recovered spermatia of 4 different Epichloë species from fly faeces. Comparison of spermatia found in fly faeces to those available from stromata showed flies avoided Epichloë clarkii and may have preferred Epichloë typhina . Interestingly, these are the only two Epichloë species known to be interfertile with one another. Individual flies tended to carry spermatia predominantly from one fungal species. Thus, flies may adopt a type of "majoring" and "minoring" behaviour when visiting fungi. Yet, Botanophila flies are not monolectic and often visited all hosts that were available within screened cages. In addition to any reproductive isolation flies may provide to some fungal species, differences in competitiveness among spermatia of different species deposited on the same stroma may favor intraspecific matings.     

Assortative mating in sympatric ascomycete fungi revealed by experimental fertilizations

Mate recognition mechanisms resulting in assortative mating constitute an effective reproductive barrier that may promote sexual isolation and speciation. While such mechanisms are widely documented for animals and plants, they remain poorly studied in fungi. We used two interfertile species of Epichloë (Clavicipitaceae, Ascomycota), E. typhina and E. clarkii, which are host-specific endophytes of two sympatrically occurring grasses. The life cycle of these obligatory outcrossing fungi entails dispersal of gametes by a fly vector among external fungal structures (stromata). To test for assortative mating, we mimicked the natural fertilization process by applying mixtures of spermatia from both species and examined their reproductive success. Our trials revealed that fertilization is non-random and preferentially takes place between conspecific mating partners, which is indicative of assortative mating. Additionally, the viability of hybrid and non-hybrid ascospore offspring was assessed. Germination rates were lower in E. clarkii than in E. typhina and were reduced in ascospore progeny from treatments with high proportions of heterospecific spermatia. The preferential mating between conspecific genotypes and reduced hybrid viability represent important reproductive barriers that have not been documented before in Epichloë. Insights from fungal systems will deepen our understanding of the evolutionary mechanisms leading to reproductive isolation and speciation.     

The Botanophila–Epichloë association in cultivated Festuca in Oregon: evidence of simple fungivory

We investigated the Botanophila (Diptera: Anthomyiidae)–Epichloë (Ascomycetes: Clavicipitaceae) interaction in cultivated Festuca spp. (fine fescue) in Oregon in western USA. Epichloë spp. are endophytic fungi of grasses in the subfamily Pooideae. They develop a felt‐like stroma on the surface of grass culms and a dense mycelium within the culms that typically prevents seed head emergence. As a result, seed yields are suppressed, and hence the disease is known as choke. Studies of Epichloë spp. on wild grasses indicate that the fly–fungus interaction is an obligatory mutualism. During oviposition, Botanophila transfers Epichloë spermatia between stromata of opposite mating types, and the perithecia that develop after fungal fertilization serve as food for Botanophila larvae. In the current study, we surveyed 19 cultivated fields of Festuca spp. in Oregon, and observed choke caused by Epichloë festucae Leuchtmann, Schardl and Siegl in 10 of these. However, perithecia were observed in only four fields, and on only 1.0–2.6% of stromata. Perithecial development was also low, and rarely covered 50% of the stroma surface. Despite the absence or low frequency of fertilized stromata, Botanophila lobata Collin larvae were present in all choke‐infested fields. Infestation levels ranged from 2.5 to 70.7%, based on an examination of 175–200 stromata from each field. Only eight (= 2%) of the 450 stromata with B. lobata had perithecia, and the greater majority of B. lobata larvae completed development and exited from unfertilized stromata. This is the first report of the B. lobata–E. festucae association in the USA, and of B. lobata larvae developing successfully on unfertilized Epichloë stromata. The average pupal weight (0.0032 g) did not differ significantly from pupae (0.0030 g) originating from larvae that had developed on fertilized stromata of E. typhina on Dactylis glomerata in a neighboring field. This result indicates that in cultivated fine fescue fields in Oregon, B. lobata forages on E. festucae, but fly development is not dependent on the fertilized stromata of Epichloë.     

Stromal Development and Mating System of Balansia epichloë, a Leaf-Colonizing Endophyte of Warm-Season Grasses

Studies of the stromal development and mating system of Balansia epichloë were conducted. Early development of the stroma consists of both endophytic and epiphytic phases of growth. As development progresses, the epiphytic stromal subiculum on the upper surface of leaves is linked with endophytic mycelium within leaves by hyphal bridges, which may provide carbohydrates for stromal development. Sugar utilization studies suggest that Balansia epichloë is excluded from growth within inflorescence primordia of grasses by the presence of high levels of sugars that are inhibitory to growth of the endophyte. Studies of the mating system of B. epichloë were conducted, and the fungus was shown to be heterothallic, with ephelidial conidia functioning as spermatia. Insect vectoring of ephelidial spermatia is suggested to account for the irregular pattern of perithecial development on stromata.     

Botanophila flies on Epichloë host species in Europe and North America: no evidence for co-evolution

Species of Epichloë (Ascomycota: Clavicipitaceae), which infect grasses, maintain an obligate symbiotic relationship with flies of the genus Botanophila (Diptera: Anthomyiidae). Sexual reproduction of the fungus usually requires a visit by Botanophila, which serves to ‘pollinate’ the fungus with spermatia of the opposite mating type; the flies in turn deposit their eggs on fungal tissues upon which the larvae feed. For a molecular phylogenetic study, a total of 108 fly larvae were collected from 10 different Epichloë species on various grasses in Europe and North America. Sequence analysis of the mitochondrial cytochrome oxidase gene (COII) detected six distinct Botanophila taxa that were associated with Epichloë. Three were restricted to samples from Europe, two to samples from North America, and one was present on both continents. In North America the common taxon [identified as Botanophila lobata (Collin)] was found on Epichloë hosts of native grasses and on Epichloë typhina (Pers.: Fr.) Tul. and Epichloë festucae Leuchtm., Schardl and M.R. Siegel of the introduced grasses Dactylis glomerata L. and Festuca rubra L., respectively. In a maximum likelihood phylogram, one of the American taxa was most basal, while the other was nested within the European taxa, suggesting that European and American taxa of Epichloë-associated Botanophila spp. may not have separate origins. Analyses of the fly populations further indicated that up to four different Botanophila taxa can be present at a single location. On taxon level there was no specificity of flies for Epichloë host species (except taxon 6 that was found only on Epichloë glyceriae Schardl & Leuchtmann), although several taxa appeared to prefer some hosts over others. Comparison of molecular phylogenetic relationships of Botanophila species with those of the associated Epichloë hosts did not suggest co-evolution of the fungus and the fly. Thus, associations between Botanophila flies and Epichloë hosts may have arisen independently more than once.     

“Pollination” of a fungus by a fly

Summary The mechanism resulting in fertilization of Epichloë typhina, a heterothallic ascomycete that is an endophytic pathogen of grasses, has now been discovered. Conidia of one mating type are produced in stromata and are then transferred by insects to individuals of the opposite mating type. One insect, Phorbia phrenione, is a particularly important vector of conidia. Once conidia of the opposite mating type have been transferred to a stroma, the life cycle continues with the formation of perithecia.     

Loline alkaloid production by fungal endophytes of Fescue species select for particular epiphytic bacterial microflora

The leaves of fescue grasses are protected from herbivores by the production of loline alkaloids by the mutualist fungal endophytes Neotyphodium sp. or Epichloë sp. Most bacteria that reside on the leaf surface of such grasses can consume these defensive chemicals. Loline-consuming bacteria are rare on the leaves of other plant species. Several bacterial species including Burkholderia ambifaria recovered from tall fescue could use N-formyl loline as a sole carbon and nitrogen source in culture and achieved population sizes that were about eightfold higher when inoculated onto plants harboring loline-producing fungal endophytes than on plants lacking such endophytes or which were colonized by fungal variants incapable of loline production. In contrast, mutants of B. ambifaria and other bacterial species incapable of loline catabolism achieved similarly low population sizes on tall fescue colonized by loline-producing Neotyphodium sp. and on plants lacking this endophytic fungus. Lolines that are released onto the surface of plants benefiting from a fungal mutualism thus appear to be a major resource that can be exploited by epiphytic bacteria, thereby driving the establishment of a characteristic bacterial community on such plants.     

Association of slugs with the fungal pathogen Epichloë typhina (Ascomycotina: Clavicipitaceae): potential role in stroma fertilisation and disease spread

Epichloë spp. are endophytes of grasses, and form epiphytic external stromata on flowering tillers. E. typhina was first noticed infecting Dactylis glomerata (= orchardgrass, cocksfoot) stands in the Willamette Valley in 1996, and soon became the primary factor limiting the longevity of seed production fields. Several species of slugs are present in these fields, and we investigated their role in E. typhina biology. Pre‐dawn surveys of D. glomerata fields in 2009 and 2010 found Prophysaon andersoni and Arion subfuscus slugs feeding on the fungal stromata. When unfertilised and fertilised immature stromata predominated, approximately 80% of the individuals of these two species that were seen on plants were found on the stromata. As the majority of stromata reached maturity the presence of these species on stromata declined to between 20–40%. The common agricultural slug pest, Deroceras reticulatum, was on stromata only 20% of the time early in the season, and declined to <5% at stromata maturity. Observations of frass from slugs determined that the most common constituent was the food sources upon which the slug species was usually found during these surveys. Typically 100% of the frass from P. andersoni and A. subfuscus contained stroma material, compared to 25% for D. reticulatum. Spermatia, and ascospores later in the season, were commonly seen in the frass of slugs that consumed stromata. Some slugs that had no stroma material in their frass appeared to have consumed spermatia and ascospores from the leaf surface. A multiple‐choice laboratory test confirmed the different proportional preferences of P. andersoni and D. reticulatum for stroma (0.72 vs 0.20) and leaf (0.07 vs 0.38), respectively. Two laboratory multiple‐choice tests, and a field survey, found that P. andersoni preferred unfertilised and immature stroma over mature stroma. D. reticulatum is the most common and abundant slug in Willamette Valley grass seed fields, yet it is the least likely to move spermatia between unfertilised stromata, or ascospores to uninfected plants. P. andersoni and A. subfuscus are mycophagous, frequently transport viable spermatia and ascospores in their frass; yet they are generally confined to field edges. Data and observations suggest the role of slugs in the epidemiology of E. typhina is small compared to other factors.     

Evidence for sexual isolation as a prezygotic barrier to gene flow between morphologically divergent species of Rhagoletis fruit flies

1. Certain groups of fruit flies in the genus Rhagoletis (Diptera: Tephritidae) are exemplars for sympatric speciation via host plant shifting. Flies in these species groups are morphologically similar and overlap in their geographic ranges, yet attack different, non‐overlapping sets of host plants. Ecological adaptations related to differences in host choice and preference have been shown to be important prezygotic barriers to gene flow between these taxa, as Rhagoletis flies mate on or near the fruit of their respective host plants. Non‐host‐related assortative mating is generally absent or present at low levels between these sympatrically diverging fly populations. 2. However, some Rhagoletis taxa occasionally migrate to ‘non‐natal’ plants that are the primary hosts of other, morphologically differentiated fly species in the genus. These observations raise the question of whether sexual isolation may reduce courtship and copulation between morphologically divergent species of Rhagoletis flies, contributing to their prezygotic isolation along with host‐specific mating. 3. Using reciprocal multiple‐choice mating trials, we measured sexual isolation among nine species pairs of morphologically differentiated Rhagoletis flies. Complete sexual isolation was observed in eight of the nine comparisons, while partial sexual isolation was observed in the remaining comparison. 4. We conclude that sexual isolation can be an effective prezygotic barrier to gene flow contributing to substantial reproductive isolation between many morphologically distinct Rhagoletis species, even in the absence of differential host plant choice and host‐associated mating.     

Stromal Development and Mating System of Balansia epichloë, a Leaf-Colonizing Endophyte of Warm-Season Grasses

Studies of the stromal development and mating system of Balansia epichlo? were conducted. Early development of the stroma consists of both endophytic and epiphytic phases of growth. As development progresses, the epiphytic stromal subiculum on the upper surface of leaves is linked with endophytic mycelium within leaves by hyphal bridges, which may provide carbohydrates for stromal development. Sugar utilization studies suggest that Balansia epichlo? is excluded from growth within inflorescence primordia of grasses by the presence of high levels of sugars that are inhibitory to growth of the endophyte. Studies of the mating system of B. epichlo? were conducted, and the fungus was shown to be heterothallic, with ephelidial conidia functioning as spermatia. Insect vectoring of ephelidial spermatia is suggested to account for the irregular pattern of perithecial development on stromata.     

Bipolar heterothallism,a principal mating system of<Emphasis Type="Italic">Cordyceps militaris in vitro</Emphasis>

Interest inin vitro study of entomopathogenic fungi, includingCordyceps species, has been increasing due to their valuable bioactive compounds and biocontrol effects. AmongCordyceps species,in vitro stromata ofC. militaris has been successfully produced and cultivated for industrial purposes. However, genetic study onin vitro stromata formation ofC. militaris has not been carried out yet. Here, relationship between mating system and perithecial stromata formation ofC. militaris is reported. Mating system was determined by observing perithecial stromata formation from mono-ascospore cultures and their pair-wise combinations. Certain combinations of mono-ascospore strains produced perithecial club-shaped stromata, whereas other combinations produced either no stromata or only abnormal non-perithecial stromata. Similarly, monoascospore cultures without combination produced either no stromata or only abnormal nonperithecial stromata. Despite obvious heterothallism, self-fertility was occasionally observed in few strains ofC. militaris. These observations indicated thatC. militaris behaves as a bipolar heterothallic fungus and requires two mating compatible strains in order to produce regular clubshaped perithecial stromata, a fundamental requirement for its industrial cultivation.     

BEHAVIORAL EVIDENCE FOR HOST-RACE FORMATION IN EUROSTA SOLIDAGINIS

We report behavioral evidence that Eurosta solidaginis, a stem-galling tephritid fly, has formed host races on its two goldenrod hosts, Solidago altissima and S. gigantea. Previous work has shown that flies from each host plant differ electrophoretically at the level of host races. The two host-associated populations were truly sympatric and were frequently found on host plants of the two species growing interdigitated with each other. Each host-associated population demonstrated a strong preference for ovipuncturing its own host. The S. gigantea–associated population emerged 10 to 14 d earlier than the S. altissima–associated population, contributing to the reproductive isolation between populations. Partial reproductive isolation is also maintained by a preference for mating on the host from which the fly emerged. The populations meet the criteria established for host races, suggesting that they may be in an intermediate stage of sympatric speciation.     

Divergence before the host shift? Prezygotic reproductive isolation among three varieties of a specialist fly on a single host plant

1. Although divergence via host‐plant shifting is a common theme in the speciation of some phytophagous insects, it is not clear whether host shifts are typically initiators of speciation or if they instead contribute to divergence events already in progress. While host shifts appear to be generally associated with speciation events for flies in the genus Strauzia, three sympatric varieties of the sunflower fly [Strauzia longipennis (Wiedemann)] co‐occur on the same host plant in the Midwestern United States and may have evolved reproductive barriers without a host shift. 2. The strength of two prezygotic reproductive barriers was compared among the three S. longipennis varieties: one barrier that is often associated with divergent ecological selection (allochronic isolation), and another that is more likely to be independent of ecological selection (pre‐copulatory sexual isolation). The presence and relative strength of each barrier between fly varieties were evaluated using microsatellites, no choice mating experiments, studies of allochronic isolation, and field collection data. 3. Evidence for both allochronic isolation and pre‐copulatory sexual isolation was detected between the three varieties of S. longipennis. The measure of isolation calculated for each barrier between the three varieties was lower than measures calculated between different species of Strauzia found on different hosts, suggesting that subsequent host shifts may increase the degree of reproductive isolation. For Strauzia and other specialist insects, some reproductive isolation may evolve prior to, and indeed may facilitate, host shifts.     

Evaluation of the potential role of water in spread of conidia of the Neotyphodium endophyte of Poa ampla

Neotyphodium endophytes are asexual, filamentous fungi, mutualistically associated with diverse cool season grasses. Infected seeds and vegetative organs of infected host plants are the only known modes of propagation of the asexual endophytes. In the last decade certain Epichloë and Neotyphodium-infected grass species have been shown to have epiphyllous structures of the endophytes, hyphae, conidiophores, and conidia, growing on leaf blades. The production of epiphyllous conidia suggests the possibility that some of these endophytes may have the ability for plant-to-plant spread. The objective of this study was to determine the possible mechanisms involved in liberation and dispersal of asexual spores of Neotyphodium growing in vitro and epiphyllously on leaves of Poa ampla. Our results indicate that water dispersal is the most likely means of dissemination of conidia of the Neotyphodium sp. Wind generated by dry compressed air does not dislodge the conidia from slide cultures or from P. ampla leaves.     

Vegetative Hyphal Fusion and Subsequent Nuclear Behavior in Epichlo? Grass Endophytes

Epichloë species (including the former genus Neotyphodium) are fungal symbionts of many agronomically important forage grasses, and provide their grass hosts with protection from a wide range of biotic and abiotic stresses. Epichloë species include many interspecific hybrids with allodiploid-like genomes, which may provide the potential for combined traits or recombination to generate new traits. Though circumstantial evidence suggests that such interspecific hybrids might have arisen from nuclear fusion events following vegetative hyphal fusion between different Epichloë strains, this hypothesis has not been addressed empirically. Here, we investigated vegetative hyphal fusion and subsequent nuclear behavior in Epichloë species. A majority of Epichloë strains, especially those having a sexual stage, underwent self vegetative hyphal fusion. Vegetative fusion also occurred between two hyphae from different Epichloë strains. Though Epichloë spp. are uninucleate fungi, hyphal fusion resulted in two nuclei stably sharing the same cytoplasm, which might ultimately lead to nuclear fusion. In addition, protoplast fusion experiments gave rise to uninucleate putative hybrids, which apparently had two markers, one from each parent within the same nucleus. These results are consistent with the notion that interspecific hybrids arise from vegetative hyphal fusion. However, we also discuss additional factors, such as post-hybridization selection, that may be important to explain the recognized prevalence of hybrids in Epichloë species.     

Distribution,host plant affiliation,phenology, and phylogeny of walnut‐infesting Rhagoletis flies (Diptera: Tephritidae) in Mexico

Many taxa of Nearctic origin have diversified in the subtropical highlands of Mexico. In particular, flies in the genus Rhagoletis have undergone episodes of isolation and gene flow during Pleistocene glaciations and post‐glacial times that have produced lineage differentiation and reproductive isolation. To reach a better understanding of the phylogeography of the genus Rhagoletis, a host plant survey of the walnut‐infesting Rhagoletis suavis species group was conducted across sixteen states comprising 34 different collecting sites in Mexico over a 9‐year period. Five species of Juglans were found to be infested by three species of walnut‐attacking Rhagoletis flies. Several species of parasitoids were also recovered from collections, but in contrast to their walnut fly hosts, they revealed little evidence for host or geographic subdivision. There was no consistent difference in mean eclosion time between walnut fly species or populations associated with different host walnuts in Mexico, unlike the case for other Rhagoletis species, in which allochronic isolation arising from variation in diapause timing is a major ecological adaptation, reproductively isolating flies. We compare the distribution of R. suavis flies in Mexico with those of other Rhagoletis species attacking hawthorns and cherries, and discuss its implications for population divergence and speciation. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 765–779.     

Epichloë typhina from toxic tall fescue grasses.

Epichloë typhina, a clavicipitaceous systemic phytopathogen, was isolated from two varieties and three hybrids of tall fescue (Festuca arundinaceae). The morphology of the fescue isolates was compared with E. typhina isolated from bent grass (Agrostis perennans). In all isolates, conidia were identical and were typical of E. typhina. In fescue grasses the endophyte failed to produce stromata, but on bent grass the fungus seasonally produced stromata, typical of the genus. Cattle grazing the fescue grasses showed signs of the fescue toxicity syndrome, the E. typhina was found in frequencies of 100%; in grasses from pastures in which cattle showed no signs of the syndrome, frequencies were 0 to 50%. Nutritional factors in vitro were more complex for the isolates from fescue than for the isolate from bent grass. These studies suggested that E. typhina includes biotypes that might be involved in the toxicity syndrome. The fescue biotypes grew poorly on media, and yields were inadequate for toxicity studies. However, the bent grass isolate grew well on three media, and extracts from two of these were toxic to chicken embryos. All isolates produced in vitro the nontoxic fungal steroid tetraenone [ergosta-4,6,8(14),22-tetraen-3-one], which has been isolated from toxic fescue grasses.     

Hybridization and sequential components of reproductive isolation between parapatric walnut‐infesting sister species Rhagoletis completa and Rhagoletis zoqui

Hybridization can provide a window into how populations diverge to form new species. Here, we confirm hybridization between Rhagoletis completa Cresson, 1929 and Rhagoletis zoqui Bush, 1966, two species of walnut husk‐infesting flies that geographically overlap in a narrow area of parapatry in Northeastern Mexico. Rhagoletis completa and R. zoqui are members of a species group (Rhagoletis suavis) that has been hypothesized to speciate in allopatry. Sexual selection has been argued to be a potentially important factor for generating pre‐mating isolation among walnut husk flies, because of the differences in wing morphology and body coloration, and the existence of sexual dimorphism within species. However, there was no evidence for pre‐mating isolation between R. completa and R. zoqui, based on choice and no‐choice mating experiments conducted on adults of fly populations outside the contact zone. There was also no support for reduced fertility of hybrid matings or for F₁ inviability; however, F₁ hybrids appeared to have lower fertility and F₂ offspring have reduced survivorship. Postzygotic isolation in later generation hybrids of mixed ancestry therefore appears to be the first intrinsic barrier to gene flow evolving between R. completa and R. zoqui. We discuss the implications of our results for allopatric speciation in walnut flies and the potential evolutionary fate of R. zoqui and R. completa if they were to come into broad geographic contact in the future. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

甘肃马先蒿寄生对禾草内生真菌共生体光合特性的影响

[目的]甘肃马先蒿与感染内生真菌的禾草(紫花针茅和麦宾草)建立根寄生关系,有关内生真菌对根寄生危害禾草光合作用调控方面的研究较少。[方法]本研究以紫花针茅和麦宾草带菌(E+)、不带菌(E-)植株为研究对象,研究甘肃马先蒿寄生和未寄生处理对紫花针茅和麦宾草E+、E-植株不同生长阶段光合特性影响的动态变化。[结果]甘肃马先蒿寄生显著降低紫花针茅和麦宾草的净光合速率、蒸腾速率和气孔导度,而胞间二氧化碳浓度和水分利用率却显著增加,这与禾草是否感染内生真菌无关。甘肃马先蒿寄生后E+紫花针茅的净光合速率、气孔导度和蒸腾速率高于E-植株,而麦宾草E+植株的净光合速率、气孔导度和蒸腾速率却低于E-植株;同时,根寄生条件下E+紫花针茅的胞间二氧化碳浓度和水分利用率低于E-植株;而E-麦宾草植株的胞间二氧化碳浓度和水分利用率却低于E+植株。[结论]内生真菌侵染影响甘肃马先蒿根寄生危害禾草的光合作用;甘肃马先蒿和内生真菌同时成为禾草营养消耗库时,内生真菌与禾草的共生关系处于一种互惠共生和相互拮抗的动态变化。