Tomatoland Read Free Page B

Saturday, and displays of cultivated tomatoes all but scream out the word diversity . Small cherry tomatoes, grape tomatoes, pear-shaped salad tomatoes, soft ball–size beefsteak tomatoes the color of fire trucks, plum tomatoes, tomatoes that are ribbed like pumpkins, tomatoes that are as perfectly spherical as a billiard ball, tomatoes that are lobed and lumpy, tomatoes that mature ninety days after being transplanted, tomatoes that require only sixty days, tomatoes that when ripe are red, pink, orange, yellow, purple, green, or any combination thereof. But all that variety is literally only skin deep. Botanists have but one name for all those oddball cultivated tomatoes: S. lycopersicum. “Most of the variation you are seeing is from a few genes that control color, shape, and size,” said Chetelat. “Other than that, there is very little genetic variation.”
    The mutant plants that theMayans domesticated were literally cut off from their ancestral roots, living in isolation more than one thousand miles away from other plants of the same species. As early farmers saved seeds from offspring of the original few plants from year to year, the population became increasingly inbred, a process geneticists call a “bottleneck effect.” Chetelat draws an example from human migration to explain this phenomenon. “Imagine a handful of people settling a new continent. They represent only a small part of the genetic diversity that was within the continent they left behind. If there’s no more migration, then the diversity is even further reduced byinbreeding.” Tomatoes went through a series of such bottlenecks in their prehistoric journey from Peru to Mexico, losing genetic diversity each time, and then went through another series of bottlenecks when conquistadores took them from Mexico to Europe.
    The problem of inbreeding is exacerbated in cultivated tomatoes because, unlike their wild brethren who must receive pollen from another plant to produce fertile seeds, they are self-pollinated.A single domesticated plant can “breed” with itself, and the resulting seeds produce offspring that are basically clones, identical to the parent plant. Not going to the bother of connecting with a mate is a rapid, surefire way to reproduce, but it further decreases genetic diversity, producing generation after generation of plants with the same traits—or lack of them. As a result, all the varieties of cultivated tomatoes that have ever been bred contain less than 5 percent of the genetic material in the overall tomato gene pool. “They seem diverse,” said Chetelat. “But at a DNA level they are very similar. If it wasn’t for the genes of these wild species, you wouldn’t be able to grow tomatoes in a lot of areas. I don’t think there is a cultivated plant for which the wild relatives have been more critical.”
    I met Chetelat and some of the offspring of those Chilean S. chilense one cool, misty January afternoon inside a greenhouse belonging to the Rick Center at the University of California Davis, which is named after its founder, the late Charles M. Rick Jr. Charlie, as his associates called him, worked at the facility until shortly before his death in 2002 at age eighty-seven. He was a legendary plant science professor, a pioneer in discovering and preserving the seventeen species of wild tomatoes, and the world’s foremost authority on the genetics and evolution of the tomato.
    Born in Reading , Pennsylvania, Rick developed a love ofhorticulture by working in apple orchards as a boy. After getting a PhD from Harvard, he moved to Davis, where he became a professor of plant genetics. Receiving a Guggenheim Fellowship in 1948, he spent a year in Peru, the first of fifteen field trips he would eventually make to South America to collect seven hundred samples of seeds and other genetic material from populations of wild relatives of tomatoes, many of which have since gone extinct in their native habitat and live on today in