The chief executive of Whole Foods Market Inc. told his board that if it bought its leading rival, the company would “eliminate forever” the possibility that anyone else could create a nationwide competitor in the natural and organic grocery business, government lawyers say.

Chief Executive John Mackey also said that buying Wild Oats Markets Inc. would let Whole Foods “avoid nasty price wars” in several cities where the two compete, the lawyers wrote in a court document unsealed on Tuesday.