Travelers come to the city of Trujillo in northwestern Peru for its elegant plazas, unsullied colonial architecture, nearby archaeological riches and even the ultrafresh local catch of its ceviche restaurants. I, however, journeyed to Trujillo in search of a sprawling, scraggly vine. It is known to botanists as Solanum pimpinellifolium, or simply “pimp.” The plant is the wild ancestor of all the tomatoes we eat today, and still grows wild in northern Peru and southern Ecuador. And although you may never have occasion to nibble one of its tiny red fruits, no bigger than a shelled pea, you owe this humble, untamed species a debt of gratitude every time you enjoy a spicy red sauce or slurp the sweettart juices of a summer beefsteak from the garden. “If it wasn’t for the genes of these wild species, you wouldn’t be able to grow tomatoes in a lot of areas,” Roger Chetelat, a renowned tomato expert at the University of California, Davis, told me before my trip to Trujillo.
Although you’d never know it from the colorful cornucopia on display at any farmers’ market on a summer Saturday, all modern domestic tomatoes (known botanically as Solanum lycopersicum) are remarkably similar. Taken together, they possess no more than 5 percent of the total genetic variation present within the wild species and primitive varieties. The domestic tomato’s progenitor has the other 95 or more percent. Modern tomatoes may taste good and offer eye appeal, but they lack many genes that allow them to fight disease and survive drought.
By contrast, the pimps and about a dozen other tomato relatives that grow wild in western South America are a tough crew, adapted to survive without the help of farmers in dramatically different climates: from some of the driest, harshest desert landscapes in the world to humid, rain forest lowlands to chilly alpine slopes. As far as we know, the inhabitants of the region never domesticated them. But a thousand miles to the north, the pre-Columbian residents of what is now southern Mexico set about planting and cultivating them, saving the seeds of those that bore the biggest, tastiest fruits and crossing desirable plants with one another. Distance prevented these early farmers from crossbreeding their new varieties with the original populations. Domesticated tomatoes may have been more palatable, but they lacked the tenacity of the ones left behind in South America. And they grew more inbred when Spanish explorers brought a few seeds from present-day Mexico to Europe, further separating tomatoes from their ancestral roots. The tomatoes grown today in the United States and elsewhere are offspring of those European strains.
Beginning in the 1940s and 1950s, botanists started correcting this problem by crossbreeding the tough untamed species with domesticated cultivars to give them the immunity and vigor of their wild relatives. Pimps alone supplied genetic traits that allow tomatoes to resist devastating fungal diseases such as late blight, verticillium wilt and fusarium wilt.
Researchers found the wild tomatoes to be so valuable that they launched expeditions to western South America to collect seeds and preserve them in climate-controlled repositories such as UC Davis’s C. M. Rick Tomato Genetics Resource Center, which Chetelat heads. The center acts like a bank, sharing its more than 3,800 specimens with breeders and scholars around the world. Like any bank, it needs a steady stream of new deposits to continue operating, and those new deposits have to come from the wild. Over the past few decades, it’s grown harder to find them. According to Chetelat, there are
two main reasons.