For the multinationals, it's biotech corporations like Monsanto, Syngenta, Bayer, Dow, and DuPont... I don't know if it's always the case, but before the farmers who used their modified seeds had to sign an agreement promising to not reuse the seeds after each harvest because there are patents on it, so patent infringement... Farmers had to pay for use them... As say @labmonkey is not GMO, but the system.
I forgot about the subject of your Phd :-)...
There are some stories with Monsanto, like GMO coton Bt (Bt » for Bacillus thuringiensis) in Africa. I find only the article in french. GMOs can be a good invention to solve food problems around the world, but that we do with it that makes issues (like all human inventions...)