It is projected to grow to more than $1 billion by 2033, fuelled by interest in its nutrition punch, according to researchers at Growth Market Reports. While most watercress is cultivated outdoors, indoor vertical farms are proving more suitable for watercress production due to higher yields, better control over environmental factors and more of the plant’s health-promoting nutrients. Researchers in the UC Davis Department of Plant Sciences are meeting the growing demand for plants that both offer greater nutrition and are suitable for indoor production.

“Watercress is the most nutrient-dense leaf on the planet,” said Professor Gail Taylor, a distinguished professor emerita in the department and Dean of the UCL Faculty of Life Sciences. Nine years ago, she started a research collection of plants drawn from botanical conservatories, seed companies and local nurseries. Pulling from that resource, a team in Taylor’s lab, led by recent PhD graduate Yufei Qian, is experimenting with 32 unique lines of wild watercress collected from 16 locations in nine countries, and they’re working with two lighting regimes. They want to develop plants with better nutrition, sensory qualities and yield – and that are well-suited specifically for indoor farming systems. The team has published a paper in Frontiers of Plant Science that offers breeders guidance for improving leafy greens growing in soil-less systems indoors. Such systems are called controlled environment agriculture.

“Up to now, there hasn’t been very much information to help breeding programmes for controlled environments,” Qian said. That’s because people breeding for CEA have very different goals and challenges compared to those breeding for field production. “For example, there is limited shelf space in CEA, so crops need to be more compact but still maintain a high yield. Pests, weather and fertilisation are better controlled in indoor growth settings, but plants must be more tolerant and adapt to the LED lights we use,” Qian explained. “We also have shorter growth cycles in CEA for consistent, high quality, year-round production.”    

As part of their study, the researchers dug deep into the natural chemicals that give watercress its peppery flavor: glucosinolates. These sulfur-rich compounds also have anti-inflammatory, antioxidant and anti-cancer properties, according to studies. The scientists discovered new glucosinolate profiles in wild watercress, said Taylor, who oversaw the research. “This offers excellent potential for developing new varieties of watercress for commercial production.”

Research team working on watercress farms


Image: Some of the undergraduate student interns who worked on the controlled environment agriculture projects with Yufei Qian include, from left: Xinyao Xu, Maddie McCormick, Nyah Mallak, Ashley Beck, Zach Orlando-Milbauer and Rex Tan. They jump for joy at the CORE greenhouse at UC Davis, where the Taylor lab’s container farm is located.
 

Researchers in the watercress facility

Image: A high school intern from Woodland contributes to harvesting and measuring watercress growing in the Taylor lab’s controlled environment facility at UC Davis.

On the UC Davis campus, a shipping container converted into a controlled agriculture facility became the proving ground. They grew the plants in that specially equipped container using two types of LED light: Normal red and blue light, and extra blue light exposure. Their goal was to understand how genetics and light interact to affect plant growth, taste and nutrition. The scientists found wide differences among the varieties. Traits such as leaf size, stem length and total biomass varied by 68% across the group. Taste-related traits, including sweetness, varied by 45%.

Watercress is especially prized for its nutritional qualities. For starters, the plant has vitamins A and C. The health-packing glucosinolates are secondary metabolites. Carotenoids are additional compounds that create red, orange and yellow colors, which benefit the eyes, skin, brain and cardiovascular system. Traits for these qualities varied by 43% among the plants studied. “This shows that wild watercress has strong natural diversity that breeders can take advantage of to improve the crop,” Qian said. When exposed to extra blue light, the plants responded differently depending on their genetic background. This means the nutritional profile of watercress is flexible, or “plastic,” and can change under different light conditions, Qian wrote.
 

Blue light in the watercress vertical farm

Image: In the Taylor lab’s container farm on the UC Davis campus, watercress grows from vertical panels, exposed only to blue LED light.

Some glucosinolates reacted to blue light in opposite ways. Other glucosinolates showed mixed responses, depending on the specific variety of the plant.

Carotenoids - especially lutein, which is important for eye health - increased consistently under extra blue light across most varieties. “Overall, they showed an active response to treatment light,” Qian said. 

However, vitamin C, glucose and overall antioxidant capacity decreased under blue light treatment compared to the control, with strong differences between different lines of watercress, including from plants collected in different areas. Using all this information, the researchers identified six promising “donor” varieties with desirable traits.

“Our next steps will be integrating useful traits of interest into a breeding population and dissecting the underlying genetic architecture to improve watercress yield, taste, post-harvest shelf life and nutritional profile better,” Qian said. “In the broader picture, this research shows the potential for controlled environment agriculture,” Taylor observed. She added, “indoor vertical farming provides us with an opportunity to change the paradigm of plant selection and breeding.” 

Many people in the Department of Plant Sciences and beyond participated in Qian’s research. Ella Katz, a UC Davis alumna and postdoctoral researcher, and Dan Kliebenstein, a professor in the department, contributed. In the UC Davis Postharvest Research and Extension Center, Adrian Sbodio and Bárbara Blanco-Ulate trained Qian to measure BRIX in watercress leaves. 

As a part of her work, Qian started a training programme in controlled environment agriculture that created mentor-mentee relationships with students. It offered hands-on experience ranging from sowing seeds, to propagation, to harvesting in a scientific experiment. The programme attracted 14 undergraduate interns from UC Davis, plus a high school summer intern from Woodland, California, and a visiting student from ETH Zurich, Switzerland. “They all contributed to this project as part of their experiential learning and are now pursuing careers around the world. It’s a very inclusive programme,” Qian said. “Students from all majors, all years, domestic and international are all welcomed here.”

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