I came across this graphic from Upworthy.com and it wonderfully illustrates what has happened to vegetable biodiversity since the beginning of “modern” agriculture. One of the primary characteristics of modern agriculture is over-reliance on a limited number of varieties of a given crop. This has led to disasters in that pest or disease attacks run from field to field over distances that cross states.
This happened with the boll weevil and cotton and with the Southern Corn Leaf Blight in corn crops. If there had been more varieties of cotton or corn planted, some would have had more resistance than others and the devastation would have been much less severe, over a smaller area, and there would have been more choices for farmers to select from to avoid future problems. With modern agriculture, the answer to these types of issues are more and more toxic poisons put on the crops and development of genetically engineered plants that also require more poisons and create many other issues.
Biodiversity is absolutely essential to solving future food scarcity issues. The demise of both crop and wild biodiversity of one of the most serious issues facing food security today. Modern agriculture has its head in the sand in this regard, aided by their agribusiness allies who want to control all seed.