Here are a couple resources that might help you find the answer to your question:

1. GMO Answers (GMOanswers.com)--there are several questions on that site about multinationals and seed companies; here is one answer, but I encourage you to go to the site and type in your own question: https://gmoanswers.com/ask/what-participation´s-percentage-monsanto-american-seed´s-general-market-and-gm-seeds-and-world

2. The Global Plant Council (http://globalplantcouncil.org/home) would very likely have your answer and perhaps a different perspective than the resource, above. They have a plethora of reports on food security (go to "resources-->reports) or simply hit the "contact us" button.

Thanks Susanne for the links. Very useful.

You can use data from FAOSTAT for soybean, corn (maize) and cotton productions from all over the world, including developing countries. Go to http://www.fao.org/faostat/en/#country, you also can compare the data of cotton, soybean and maize /corn at http://www.fao.org/faostat/en/#compare from any country you want