Method for screening Cu, Zn or Pb phytotoxicity on switchgrass and reed canarygrass

In North America, there is a large number of trace metal (TM) contaminated sites, which cannot be used for human or animal food production. Using these sites for the production of dedicated energy crops could represent a sustainable alternative to the use of good quality agricultural soils. This project aims at developing a new screening method to identify more tolerant TM genotypes in switchgrass (Panicum virgatum L.) and reed canarygrass (Phalaris arundinacea L.). This method relies on successive contamination stresses at the level at which the biomass DM yield is reduced by 50%. The determination of these levels for Cu, Zn, and Pb is essential to apply the appropriate stress to each species. We used five cultivars for switchgrass and two cultivars for reed canarygrass. Plants were sow in a sandy mix substrate and allowed to grow in a control environment for 4 weeks prior to being transplanted in a sandy mix containing either copper (0, 150, 275, and 525 mg of Cu kg-1 substrate), zinc (0, 300, 550, 1050 mg of Zn kg-1) or lead (0, 1000, 2000, 4000 mg of Pb kg-1). Eight weeks after transplantation, plants were harvested and biomass DM yield was measured. For switchgrass, the biomass was reduced 50% when 210 mg of Cu, 1020 mg of Zn, or 1500 mg of Pb was added to the substrate. For reed canarygrass, the biomass was reduced by 50% when 525 mg of Cu, 1050 mg of Zn, or 2175 mg of Pb was added to the substrate. Based on these results reed canarygrass seems to be more tolerant to TM contamination than switchgrass. These data will be particularly useful to identify more tolerant TM genotypes within switchgrass and reed canarygrass breeding material. This is required to develop breeding populations, and to accelerate the development of cultivars adapted to contaminated sites.