Crop Diseases That Changed What the World Grows

Wheat stem rust has caused some of history's most severe wheat famines, and its dark pustules can destroy a crop within weeks. The Ug99 race that emerged in Uganda in 1998 can overcome resistance genes bred into most of the world's wheat, which set off a global breeding effort.

Rice blast is considered the most destructive disease of cultivated rice worldwide. The same fungus in a host-adapted form also causes wheat blast, an emerging concern in South America and South Asia, so the threat to rice is tied to the threat to wheat.

Fusarium head blight shrivels the kernels of wheat and barley and contaminates grain with vomitoxin and other mycotoxins that are regulated in food and feed. Severe epidemics in North America and Europe in the 1990s and 2000s caused billions of dollars in losses and market rejections.

Karnal bunt was first described near Karnal, India in 1931. It causes only modest direct yield loss, but infected grain is unmarketable and importing countries enforce strict quarantine, so a detection can trigger major trade restrictions.

Take-all blackens the roots and stem bases of wheat and barley and builds up in soil under continuous cereal cropping. It typically declines after several years of wheat, a process called take-all decline that is a well studied example of soil suppressiveness.

Ergot replaces developing rye kernels with dark, alkaloid-rich sclerotia. Contaminated flour caused the epidemics of gangrene and convulsions in medieval and early modern Europe known as St Anthony's Fire, and grain trade still sets strict tolerances because the alkaloids remain toxic.

Late blight is a water mold, long grouped with fungi in agricultural practice, that rots potato leaves, stems and tubers. It caused the Irish potato famine of the 1840s and remains one of the costliest plant diseases in the world.

A strain of southern corn leaf blight adapted to the Texas male sterile cytoplasm used in United States hybrid seed caused the 1970 corn blight epidemic, destroying roughly 15 percent of the national maize crop. It remains a textbook warning about genetic uniformity in breeding.

Coffee leaf rust devastated coffee production in Ceylon in the nineteenth century, effectively ending the island's coffee industry and prompting a shift to tea. A severe epidemic across Central America between 2012 and 2014 caused billions of dollars in losses and displaced hundreds of thousands of coffee workers.

An earlier race of the Panama disease fungus wiped out the dominant Gros Michel banana in the mid twentieth century. Tropical race 4 now attacks the Cavendish, persists in soil indefinitely and has no effective chemical control, so it is regarded as the greatest threat to the global banana industry.

Black Sigatoka cuts yields by up to 50 percent in untreated banana plantations and has largely displaced the earlier yellow Sigatoka. The intensive fungicide programs needed to control it are a major recurring cost in commercial banana production.

Soybean rust was long established in Asia and Australia before it reached South America in 2001 and the continental United States in 2004. Its wind-dispersed spread led several affected countries to set up national spore tracking and forecasting networks.