I read this years ago, but Monsanto's genetically modified corn seeds had something they referred to as a "terminator" gene, which is what made the genetically modified plants single generation. However, when natural plants were pollinated with pollen from genetically modified plants (my biology is probably wrong here), seeds the natural plants produced retained the terminator gene.

Extrapolate this out to the worst-case scenario and you've got the entire world buying corn seed from Monsanto because natural corn is extinct, through decades of unintentional pollination.