Environmental context of endophyte symbioses: Interacting effects of water stress and insect herbivory

Symbiotic associations between grasses and fungal endophytes are generally regarded as mutualistic, yet benefits to host plants may vary with environmental context. Previous studies have emphasized how endophytes influence plant responses to single stressors. In contrast, the outcome of endophyte-grass interactions under simultaneous biotic and abiotic stresses remains poorly explored. We hypothesized that benefits from endophyte symbiosis become most apparent in "complex" environments where hosts experience multiple stresses. We evaluated the performance of endophyte-infected (E+) vs. endophyte-uninfected (E-) Lolium multiflorum plants in a factorial experiment with water supply (control vs. drought) and insect herbivory (with aphids vs. without aphids). Endophyte infection delayed tiller production in well-watered plants, while water stress reduced tillering in E- plants. Endophyte mediation of herbivory tolerance was contingent on water supply. Whereas aphid herbivory was detrimental to E+ plants in well-watered soils, aphids interacted with drought stress in decreasing the reproductive output of E- but not E+ plants. Moreover, endophyte presence decreased aphid densities on drought-stressed plants only. Thus, endophyte symbiosis enhanced host tolerance to overlapping biotic and abiotic stresses, although infected plants failed to outgrow their uninfected counterparts. These results support the view that mutualistic endophyte effects may not arise in low-stress environments. © 2011 by The University of Chicago. All rights reserved.Fil: Miranda, M. Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Omacini, Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Chaneton, Enrique Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin

Imperfect Vertical Transmission of the Endophyte Neotyphodium in Exotic Grasses in Grasslands of the Flooding Pampa

Fil: Gundel, Pedro E. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas vinculadas a la Agricultura; Argentina.Fil: Garibaldi, Lucas Alejandro. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche. Laboratorio Ecotono; Argentina.Fil: Tognetti, Pedro M. Universidad de Buenos Aires (UBA). Facultad de Agronomía; Argentina.Fil: Aragón, Roxana. Universidad de Buenos Aires (UBA). Facultad de Agronomía; Argentina.Fil: Ghersa, Claudio M. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas vinculadas a la Agricultura; Argentina.Fil: Omacini, Marina. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas vinculadas a la Agricultura; Argentina.Fil: Gundel, Pedro E. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Fil: Garibaldi, Lucas Alejandro. Universidad de Buenos Aires (UBA). Facultad de Agronomía; Argentina.Fil: Ghersa, Claudio M. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Fil: Omacini, Marina. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Cool-season grasses establish symbioses with vertically transmitted Neotyphodium endophytes widespread in nature. The frequency of endophyte-infected plants in closed populations (i.e., without migrations) depends on both the differential fitness between infected and non-infected plants, and the endophyte-transmission efficiency. Most studies have been focused on the first mechanism ignoring the second. Infection frequency and endophyte transmission from vegetative tissues to seeds were surveyed in two grasses growing in vegetation units that differ in flood and grazing regimes, and soil salinity. Transmission efficiency and infection frequency for tall fescue did not vary significantly and were 0.98 and 1.00, respectively. For Italian ryegrass, transmission efficiency and infection frequency were 0.88 and 0.57 in humid prairies, and 0.96 and 0.96 in the other vegetation units. Only in humid mesophytic meadows, the observed pattern was irrespective of the presence or absence of grazers. Our results suggest that selection forces for endophyte infection are different for both species. Imperfect transmission was only compensated in tall fescue through an increased fitness of infected plants. Interpreting variations of infection frequency only in terms of differential fitness can be misleading, considering that endophyte transmission can be imperfect and variable in nature. Therefore, this study highlights the importance of measuring transmission efficiency

Mutualism effectiveness and vertical transmission of symbiotic fungal endophytes in response to host genetic background

838-849Certain species of the Pooideae subfamily develop stress tolerance and herbivory resistance through symbiosis with vertically transmitted, asexual fungi. This symbiosis is specific, and genetic factors modulate the compatibility between partners. Although gene flow is clearly a fitness trait in allogamous grasses, because it injects hybrid vigor and raw material for evolution, it could reduce compatibility and thus mutualism effectiveness. To explore the importance of host genetic background in modulating the performance of symbiosis, Lolium multiflorum plants, infected and noninfected with Neotyphodium occultans, were crossed with genetically distant plants of isolines (susceptible and resistant to diclofop-methyl herbicide) bred from two cultivars and exposed to stress. The endophyte improved seedling survival in genotypes susceptible to herbicide, while it had a negative effect on one of the genetically resistant crosses. Mutualism provided resistance to herbivory independently of the host genotype, but this effect vanished under stress. While no endophyte effect was observed on host reproductive success, it was increased by interpopulation plant crosses. Neither gene flow nor herbicide had an important impact on endophyte transmission. Host fitness improvements attributable to gene flow do not appear to result in direct conflict with mutualism while this seems to be an important mechanism for the ecological and contemporary evolution of the symbiotum

Fungal Endophyte Diversity in Sarracenia

Fungal endophytes were isolated from 4 species of the carnivorous pitcher plant genus Sarracenia: S. minor, S. oreophila, S. purpurea, and S. psittacina. Twelve taxa of fungi, 8 within the Ascomycota and 4 within the Basidiomycota, were identified based on PCR amplification and sequencing of the internal transcribed spacer sequences of nuclear ribosomal DNA (ITS rDNA) with taxonomic identity assigned using the NCBI nucleotide megablast search tool. Endophytes are known to produce a large number of metabolites, some of which may contribute to the protection and survival of the host. We speculate that endophyte-infected Sarracenia may benefit from their fungal associates by their influence on nutrient availability from within pitchers and, possibly, by directly influencing the biota within pitchers

Broad-scale variation of fungal-endophyte incidence in temperate grasses

1.The strength of many interactions between plants and other organisms changes across regional gradients. For example, the relevance of plant-herbivore interactions increases with primary production. Likewise, biotic interactions collectively become more intense from the poles to the equator. Yet, the regional variation of the interaction between grasses and systemic fungal endophytes, which provide resistance to biotic and abiotic environmental factors (i.e. herbivory and drought), is poorly understood.2. We compiled 1008 records of the incidence level of fungal endophytes (Epichlo?e, Ascomycetes: Clavicipitaceae) on wild populations of 48 cool season grasses, encompassing 10 biomes across a broad latitudinal expanse and primary production gradient. Symbiosis incidence was analysed as a function of mean primary production, precipitation, temperature and latitude of each site, which in turn were obtained from climatic and satellital sources.3. Across a 30-fold variation of mean primary production, average symbiosis incidence increased from 20% to 70%. The pattern became stronger when the analysis was restricted to the single grass genus Festuca, which accounted for half of the total data.4. The number of grass populations showing no symbiosis incidence (0%) decreased as primary production increased, whereas those with 100% of incidence increased.5. Primary production at the regional scale was negatively correlated with latitude but positively with mean annual temperature and precipitation. Symbiosis incidence was similarly correlated with latitude and temperature, and it was not with mean annual precipitation. 6. Synthesis. Different descriptors of this grass-fungus symbiosis show that average incidence in wild populations world-wide increases with mean primary production. As at large spatial scales herbivory and temperature increase and aridity decreases with primary production, our results suggest that, at broad-scales, these biotic and abiotic factors may be important drivers of the symbiosis success.Fil: Semmartin, María Gisela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Omacini, Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Gundel, Pedro Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Hernández Agramonte, Ignacio M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin