China’s agtech is modernizing, and the Americas and Europe is already modern. We divert enough calories for 1 billion people into biofuels. The only realistic thing that will cause a famine is a breakdown in global trade/markets. I think you are being overly dramatic about the disease threat. I am not quite sure why you think genetic diversity within a species is so important. What is important is to have species diversity and trade to avoid potato famines.