Development of a native Pascopyrum smithii (Western wheatgrass) cultivar favored endophyte effects

Background/Question/Methods

Fungal endophytes are common within the Pooid grasses and their associated cultivars.  While much is known about the effects of endophyte presence within a select group of mostly introduced species, relatively little is understood about the effects of endophyte presence within native North American grasses and their associated cultivars. The purpose of our study was to test whether fungal endophyte presence in the cool-season grass Pascopyrum smithii (Western wheatgrass) affects the structure of above- and belowground communities and whether these effects are consistent between native and cultivar populations.  In summer 2012, we planted plots (0.5 m x 0.5 m) with 16 transplants developed from endophyte-positive and endophyte-free individuals originating from a native population or a cultivar (Rodan).  Plots were planted with either consistently testing endophyte-positive (E+) or endophyte-free (E-) individuals of a single population type.  A 0.25 m weeded buffer was maintained surrounding each main-plot in order to track endophyte effects on host tillering.  Above-ground biomass within the main-plot and the buffer was harvested, dried, and weighed.  Soil samples were collected for nematode community analysis, root analysis, and nitrogen availability.  In addition, Bio-log EcoPlates^TM were used to test for differences in the soil bacteria metabolic profile.

Results/Conclusions

Endophyte presence within the cultivar, but not in the native population, affected host growth and belowground community structure in the first growing season.  Endophyte presence did not affect main-plot aboveground biomass, but in the Rodan cultivar buffer biomass was greater in E+ plots than in E- plots. Rodan is marketed as a high-tillering cultivar and it appears that the increased propensity to tiller is associated with endophyte presence.  Root biomass, total nematode abundance, and nitrogen availability were not affected by endophyte presence. However, the soil metabolic profile differed between E+ and E- Rodan plots (96 hour incubation; A = 0.015, p = 0.018), which indicates endophyte presence may also affect belowground composition and processes.  The absence of these effects in the native population, indicates that effects associated with endophyte presence may have been selected for in the cultivar development process.  Our findings support the notion that endophyte effects within cultivars of other species may have been selected for during cultivar development and are not necessarily representative of endophyte effects in natural populations.