The Last Harvest: The Genetic Gamble that Threatens to Destroy American Agriculture.

• Author: Easterbrook, Gregg

Readers who peruse the recent bestseller The Hot Zone, whose flap copy suggests that a frightful virus accidentally set loose by a government lab near Washington, D.C. will "kill 9 out of 10 people" in the area within days or even hours, may notice that by the end of the tale - ah, no one's dead. The Hot Zone became both a hot book (deservedly: it's a good read) and the inspiration for two big-studio movies despite the fact that the very thing it concerns, the unstoppable runaway of a virus worse than bubonic plague, did not happen.

Paul Raeburn faces the same problem - writing about something that hasn't happened - in his new book The Last Harvest, and handles it well. Where The Hot Zone had Hollywood-esque aspects such as calls to the President and commando teams wearing biological protection suits, The Last Harvest has assistant professors in beat-up jeeps looking for potato roots in Mexico. Yet the disaster of which The Last Harvest warns is in some ways more compelling than an outbreak of a killer disease. It is Raeburn's thesis that modem farming, based mainly on cloned seed groups from a comparatively narrow genetic background, has put American agriculture in danger of "catastrophic losses" for which there may be no immediate antidote.

Raeburn, the science editor of the Associated Press, relates many chilling stories of the narrowing genetic base of modern farming. Fifty years ago, he writes, the Texas wild rice strain called Zizania texana was common around the San Marcos River near San Antonio. But development has altered most of the natural habitat for Z. texana, a plant some agronomists think holds tremendous genetic potential. Attempts to preserve the plant by breeding it away from the San Marcos River have not been successful.

This is a problem some researchers call "genetic erosion." Plant breeders need wild genes to generate crosses when a new blight or insect attacks crops. Though doomsday estimates for world species loss are almost certainly exaggerated, they need only be a little right - far less than half right - to mean that wild genes for plants are "eroding" at an alarming pace. Western agriculture is...