The spores arrived from Kenya on dried, infected leaves ensconced in layers of envelopes.

Working inside a bio-secure greenhouse outfitted with motion detectors and surveillance cameras, government scientists at the Cereal Disease Laboratory in St. Paul, Minn., suspended the fungal spores in a light mineral oil and sprayed them onto thousands of healthy wheat plants. After two weeks, the stalks were covered with deadly reddish blisters characteristic of the scourge known as Ug99.

Nearly all the plants were goners.

Crop scientists fear the Ug99 fungus could wipe out more than 80% of worldwide wheat crops as it spreads from eastern Africa.