Just four companies control more than 60% of the global market.

In response to anxieties, Paolo Arrigo of Franchi Seeds is selling Brexit "survival kits." They're a hit.

As companies like Monsanto and DuPont gain patent rights to seeds, one group of plant breeders is trying to create an alternate open access seed market.

For crops where GMO seeds are big, they're 90 percent of the market