It’s a battle cry that you can find emblazoned on shirts and hats and hear from many Mexicans and members of that diaspora — including an ever-expanding throng of chefs, bakers, and restaurateurs.

IXTENCO, Mexico — On the slopes of the Malinche volcano, Juan Vargas starts the dawn routine he’s had since childhood, carefully checking stalks of colorful native corn. For years, Vargas worried that ...