The ecotype and population differences in mycorrhizal responsiveness associated with switchgrass

Background/Question/Methods

High nutrient and water use efficiency associated with effective mycorrhizal symbioses is critical to the sustainable and economical biomass production of switchgrass as a cellulosic bioenergy crop and successful restorations. We present information on the relative mycorrhizal responsiveness (rMR = (M_myco –M_nonmyco)/M_nonmyco), where M is total dry mass) of switchgrass ecotypes representing upland and lowland populations.  We evaluated 20 populations collected over a wide geographical range comprising the natural habitats of switchgrass (Panicum virgatum) in North America.  Ecotypes were grown for 16 weeks in soil collected near Manhattan, KS.  Soils were either steam-pasteurized (nonmycorrhizal), or non-steamed native prairie (mycorrhizal). 

Results/Conclusions

We find evidence of a strong genetic component for rMR in switchgrass.  Within switchgrass ecotypes rMR is directly related to whether ecotypes were derived from upland or lowland populations, with upland populations expressing a significantly higher rMR than lowland populations (ANOVA, P<0.0001).  We also find rMR maps at a continental scale in a manner similar to the distributions of upland and lowland populations, with highest levels of rMR being found in the Central Great Plains. Also, evidence is presented that through selective breeding rMR can be increased in lowland populations to levels usually associated with upland populations.  These findings indicate that it is possible to genetically improve a sustainability trait like rMR in switchgrass.   Other experiments are proposed to better understand the mechanisms controlling rMR in switchgrass.