Charley Ricks Hunt for Wild Tomato Genes

Renowned geneticist Charles M. Rick spent 50 years collecting specimens of the stinky, sour-fruited South American vines from which all cultivated tomatoes arose.

| Summer 2018

Tomatoes are a wonderful example of how we humans created a modern fruit. Modern tomatoes (Solanum lycopersicum) are far removed from their wild ancestors in both taste and appearance, and they’re also remarkably homogeneous, despite the range of colors, shapes, and flavors heirloom tomatoes exhibit. The domesticated tomato has gone through several genetic bottlenecks as travelers carried tomato seeds from the Andes in South America to Mesoamerica, then to Europe, and from there to the rest of the world. Each time people carried the tomato over a long distance, only a handful of seeds from the source location made the trip. By the time travelers and explorers introduced the tomato to Europe, cultivated tomatoes had only 5 percent of the genetic variation of their wild relatives. And yet, the modern tomato sits atop the produce heap as the No. 1 fruit vegetable — produce that’s commonly considered a vegetable, although botanically it’s a fruit — produced in the world.

In Search of Genetic Diversity

To better understand tomato genetics, and with particular interest in wild tomatoes’ resistance to pests and drought, the late botanist Charles M. Rick made a number of trips to the western coast of the Andes, where tomatoes originated. Once described as “Charles Darwin and Indiana Jones rolled into one,” Charles explored Peru, Ecuador, and Chile for wild populations of tomato species and other members of the nightshade family over a 50-year period, starting in the 1940s, and he brought his family along on many of his expeditions.

The western Andes are a rich genetic source for tomatoes, and a challenging place to collect samples. In the shadow of the Andes — running 4,700 miles from Panama in the north to the southern tip of South America — lies roughly 300 miles of foothills and coastal plains sloping down to the Pacific Ocean. More than 50 rivers drain off the steep western slopes, more or less straight into the Pacific Ocean. The river valleys are separated by miles of dry land, making the valleys “island” habitats, in geneticist terms. The intervening inhospitable ground effectively cuts off gene exchange among plants in different river valleys, which allows them to develop in vastly different ways without being influenced by other species. It is here, in the western Andes, that the story of domesticated tomatoes begins.

John Rick remembers his father as “Charley” Rick, a treasure hunter in many ways, but far from seeking ancient relics, he was after plant diversity in the form of particular wild relatives of modern tomatoes. Finding his treasures was a matter of locating plant populations by poring over old herbarium records and making educated guesses from local topography. His field excursions to collect and record wild tomatoes in their native environments provided crucial information in identifying the wild ancestors of modern cultivated tomatoes, and his research efforts led to his election to the National Academy of Sciences in 1967.

Into the Field

In 1956, when John was 6 years old and his sister, Susan, was 10, getting anywhere took a lot more time than it does now. Getting from San Francisco to Lima, Peru, for example, took several weeks by freighter. But John remembers such travel as part of a glorious adventure — no doubt a view of the world influenced by his father. John explains that Charley “knew how to get himself out of things; he had an excellent sense of do-it-yourself-ism.” To Charley, it didn’t matter what the situation was; it was all fun.

That cheerful approach to travel was essential, because the Rick family’s self-made expeditions out of Lima, Peru, invariably met with one challenge after another. They never knew exactly where they’d end up. Sometimes, when John asked where the family was going to sleep, Charley’s answer was, “We have sleeping bags, don’t we? We’ll just bunk down here.” When they had a hotel room, sometimes the hotel was nothing more than “a few walls which were less walls than holes.”

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