Ecology of fungal root endophytes in a changing climate: A case study with taxa of the Phialocephala fortinii s.l. - Acephala applanata species complex [thesis]

Vanessa Reininger, Ottmar Holdenrieder, Erhard Halmschlager
Every plant is supposed to host endophytic microorganisms, which can colonize all plant organs without causing any harm. A very common group of fungal endophytes are ascomycetous dark septate endophytes (DSE). Fungi of the Phialocephala fortinii s.l. -Acephala applanata species complex (PAC) belong to this group and colonize roots predominantly of coniferous trees and ericaceous shrubs in the Northern hemisphere. Recent studies showed that the behavior of PAC on the host plant depends on its
more » ... t depends on its genotype and ranges from neutral to pathogenic, and that some strains provide biological control of serious root pathogens. Nevertheless, our understanding of the mechanisms leading to community formation and the ecological role of these fungi is still very limited. Since PAC endophytes are very common and several species and genotypes can live spatially closely together, PAC species and genotypes are supposed to interact with each other and with other microbes, e.g. ectomycorrhizal fungi (ECM). Considering that plant communities are presumably shaped by the microbial communities they host, PAC might contribute significantly to this process. Therefore, interaction studies using clearly defined PAC strains investigating their intra-and interspecific competition as well as the effects of PAC communities on different host plants are needed. Microbe-microbe and microbe-plant interactions are strongly influenced by environmental factors. However, nothing was known about the effect of global warming on the PAC-plant symbioses. Therefore, the effects of rising temperatures on a tripartite system, comprising host plants, different PAC genotypes and ECM were addressed for the first time in this study. Two multifactorial interaction experiments were performed to investigate PAC's competitive behavior in the host. (1) In the first experiment, intra-and interspecific competition was studied among four PAC strains (two strains each of two species) differing in pathogenicity on Picea abies. The strains were used to inoculate two host species (Betula pendula and Picea abies) which were incubated at two temperatures (18°C and 23°C). Single-strain and dual-strain treatments were performed to test fungal interactions and to reveal the effect of the genetic diversity of PAC endophytes on the host plant. (2) In the second experiment PAC-ECM interaction was tested using the same four PAC strains in competition with the ectomycorrhizal fungus Laccaria bicolor S238N on two host species (Pseudotsuga menziesii and Picea abies) and at two temperatures (19°C and 25°C). Measured variables were plant dry weight, fungal biomass in both experiments and the degree of mycorrhization in the second experiment. To analyze these experiments, a method based on competitive microsatellite PCR was developed to quantify endophytic biomass of two PAC strains in the same root sample. PAC biomass was used as an estimate for competitive success. SUMMARY 2
doi:10.3929/ethz-a-007348443 fatcat:quyuumyt4bagpnhiv4gnqc3mp4