Tomato growers know that using less water just before the harvest concentrates the sweetness and acidity of their fruit. To compound that burst of flavor, a smart gardener or farmer might choose to grow varieties of tomato plants known for their tolerance of dry-weather conditions. But exactly how little water can tomatoes survive on, and what genes help them do it? Scientist Leah Rosental is on a mission to find out.
Working with the Ben Gurion University of the Negev in Israel, Rosental is testing an astonishing 360 tomato varieties for their drought-tolerance. The greenhouse where she conducts her research is an organized jungle of 2,400 individual plants in various states of success and distress. At the time of my visit, Rosental is three weeks away from the last day of her experiment. Half of the plants are on a strict regimen of a mere 10 percent of their normal irrigation schedule.
Tucked in and among the lackluster leaves and sagging stems, there are colorful salad tomatoes shaped like blocky bell peppers and ripe purple figs. There are peach-sized tomatoes ripening to a plummy-chocolate color and red tomatoes with zebra-type stripes flecked with gold. Pointing above her head to a cascade of petite cherry tomatoes growing in thick clusters, Rosental smiles. "Look up," she says, "This one is called 'Pearl.' It's like standing under a galaxy of tomatoes." A galaxy wouldn't be entirely out of place. Rosental uses a mass spectrometer to identify around 300 chemical compounds in her tomato fruits—the same cool tool that astrophysicists have sent to other planets to map their chemical composition.
Where a gardener might scratch their head at a droopy tomato plant, making note of stunted growth or the development of blossom end rot, Rosental is able to look at the chemical fingerprints of these changes by analyzing the tomato's metabolomic data (all of its compounds and metabolites), creating a kind of snapshot of the plant's physiological state. Identifying the changes in a tomato plant that help or hinder its ability to handle extreme drought has an obvious importance for growers in saline or dry conditions like the desert. But the Brotman Lab, where Rosental works, is thinking globally. After identifying the genetic markers in tomatoes that make them drought-tolerant, their published discoveries are available for seed-breeders and scientists developing tomatoes for market. These more robust seeds are passed on to farmers and gardeners anywhere in the world looking to navigate changes and extremes in seasonal weather, or to use water more responsibly.
After a season of reduced irrigation, Rosental records which plants wither and which yet bear tasty, weighty fruit. When the tomatoes are ripe, the team descends on the greenhouse for a big harvest. I am visiting on one such day. A neatly labeled brown paper grocery bag placed at the base of each plant will be full of fruit by the time I leave. Rosental and her team will measure, weigh, and photograph just five of the most average fruit from each plant.
I do a quick calculation, then ask eagerly what happens to the hundreds of pounds of tomatoes that remain. Rosental is a mother of two. Are her kids sick of tomatoes yet? "Giving away the fruits was a great way for the lab to meet the community," she says, "Usually we research bacteria and proteins, not tasty tomatoes." Mentally, I take pasta marinara and gazpacho off tonight's menu. But in the future—thanks to the work of scientists like Rosental and the seed breeders who grow from her data—tasty, resilient tomatoes await me as a gardener.