PARIS — Guy Sant is distressed about the sorry state of his mushroom business this year. Usually in the autumn, when the weather turns brisk and the leaves begin to fall, his pickers gather 60 tons of wild fungi to satisfy European consumers, he said. This fall, they found only 16 tons. “I lost so much this year, I may have to close,” he said bleakly.

Mr. Sant, who runs Cevennes-Truffes, a mushroom company based in St. Anastasie in southern France, says he knows who to blame: outsiders, mostly from Eastern Europe, who at the behest of sellers in Spain have come across the border and hauled away wild mushrooms by the truckload. Even the way the outsiders picked the mushrooms made it unlikely they would grow again next season, he said.

While experts dispute that last claim, it is revealing both of one of the more idiosyncratic corners of the French psyche, in which wild mushrooms are viewed as a national patrimony, and also of the frustrations of some French as a borderless Europe opens once exclusively French domains to new economic competitors.

That competition has brought with it darker undercurrents of discrimination and hostility toward the European Union’s newest — and poorest — citizens from Bulgaria and Romania, and especially the Roma, who are a minority of 20,000 in France. In recent months, France’s interior minister called for the Roma to be expelled and a 15-year-old Roma girl was taken off a school bus in front of classmates and deported with her family.