Southern corn leaf blight (1970-1971)
A fungal disease destroyed about 15% of the U.S. corn crop in 1970. Most commercial corn shared the same susceptible cytoplasm, a genetic vulnerability created by decades of breeding for uniformity.
Farmers lost hundreds of millions of dollars; seed companies scrambled for resistant varieties.
The episode pushed the USDA to expand germplasm preservation and diversify breeding programs.
The same logic — that genetic uniformity is a national security risk — drives today's push to sequence and understand the seed bank.
