Seeds, plants, and substrates used in this study. (A) The three juvenile plant genotypes at the five leaf stage growing in Canadian soil are shown (from L to R): ancestral Parviglumis teosinte (red stakes), traditional Mexican landrace Mixteco (blue stakes), and the modern temperate hybrid Pioneer 3751 (purple stakes). (B) Examples of seed are shown (from L to R): Parviglumis, Mixteco and Pioneer 3751. (C) Pot substrates are shown (from L to R): sterilized sand, Canadian agricultural soil, and Mexican soil from a Parviglumis field. The scale bars on the left equal 10 mm. For a physical and chemical comparison of Canadian and Mexican soil, see Additional file 1: Table S1.