MADAWASKA, Maine — Growing up on his father’s potato farm in Cyr Plantation, Dominic LaJoie said he never could have imagined the size his family’s company, LaJoie Growers LLC, would reach. He also never planned on getting into politics. Nonetheless, the National Potato Council elected LaJoie, a fourth-generation St. John Valley potato farmer, president of the Washington, D.C.-based interest group on Feb.