Doing the Tango has been a fruitful dance for UC Riverside and the worldwide citrus industry.

First released to growers in 2006, the UCR-developed Tango mandarin has established itself as a symbol of innovation and sustainability in the global citrus market. It has generated more than $70 million in cumulative economic value for UCR, making it one of the most successful innovations in UC history, according to University of California system data.

The Tango mandarin. (Photo/UCR)

Marketed to consumers under brand names such as Cuties®, Halos®, and Tango Fruit®, among others, the tasty, virtually seedless, easy-peeling fruit became a worldwide favorite — a convenient, healthy snack for consumers and a reliable, profitable crop for growers.

Now, after nearly two decades of exclusivity in the U.S., the Tango has reached a milestone. The U.S. plant patent for Tango has expired, allowing domestic growers to freely plant the variety without paying royalties.

Plant variety protection for the Tango will continue internationally, meaning royalties will still flow from international growers. But in the United States, the Tango is now open to all — from major citrus producers to home gardeners.

Its 20-year run has essentially reshaped the citrus industry.

According to the California Department of Food and Agriculture, in 2024, the Tango accounted for nearly 20,000 acres, or 32 percent of all mandarin acreage in the state — the largest share of a single mandarin variety. The U.S. Department of Agriculture estimated the total production value of mandarins in California at $855 million during the 2024–25 season, meaning Tango alone contributed about $272 million to that total.

Globally, the Tango is now grown in more than 20 countries and marketed worldwide in more than 50 countries. Just this month, a European trade association named it "Flavor of the Year" in Spain and Portugal.

Brian Suh

“Taking into account the entire supply chain, from nurseries and farms to packers, transporters, and retailers, Tango has revolutionized the citrus industry in its 20 years of existence, generating a significant economic impact each year,” said Brian Suh, UCR’s senior executive director of technology partnerships.

The Tango began as an experiment by Professor Mikeal Roose, a citrus geneticist, and Timothy Williams, a longtime staff research associate and citrus breeder, both in UCR’s Department of Botany and Plant Sciences. With support from the California Citrus Research Board, they set out in the 1990s to develop a mandarin that would stay seedless no matter what citrus varieties bloomed nearby.

To accomplish that goal, the UCR team turned to gamma irradiation, exposing the buds of another mandarin variety to a safe and brief dose of radiation to trigger DNA changes that might yield the desired trait.

Low-dose gamma radiation constantly bombards Earth and could naturally trigger a mutation for a seedless variety of mandarin. But such occurrences are extremely rare. Exposing mandarin buds to higher but controlled doses in the laboratory essentially sped up the process, Roose explained.

The researchers grafted the irradiated buds onto rootstock and grew them in greenhouses before planting them outdoors. About 200 trees were planted. Some withered. Some produced good-looking fruit but still had seeds.

“Some genetic changes happen, some don’t,” Roose said. “You just have to grow the trees and wait — sometimes for years — to see what you’ve got.”

After several seasons, seven trees looked promising, but only two truly stood out. Then came the deciding moment, with their final selection winning over another tree that just happened to have a few more seeds.

That selection became the Tango.

An appealing variety

The variety offered several advantages to growers serving a global market that demanded low-seeded or seedless fruits.

Importantly, the Tango’s ovules — structures inside the ovary of flowers that normally develop into seeds after fertilization — are highly sterile, which means seeds can’t form. Its pollen is also sterile. So, the Tango doesn’t contribute to seed formation in other varieties planted near Tango trees.

These traits were welcomed by growers of other varieties. Growers no longer had to take costly actions to keep bees away to prevent pollination and avert seed formation. Such actions included draping trees with nets, growing mandarins in isolation, and paying beekeepers to relocate their apiaries, among other strategies.

The need to keep bees away also limited mandarin growers’ ability to grow other crops, and put them in conflict with neighboring farms and beekeepers.

The Tango offered other clear advantages as well.

“It’s very easy to grow in the nursery,” Roose said. “It works well on the main rootstocks we use, grows vigorously in the field, and produces heavy yields. You do have to manage it carefully, so it doesn’t overbear — which is common in mandarins — but otherwise it’s a dream variety for growers.”

For consumers, the appeal was clear. The fruit peels cleanly, fits in a lunchbox, and delivers a bright, sweet flavor that doesn’t require refrigeration. Its firm skin and long shelf life made it ideal for global shipping. And it’s a late-season producer, extending the availability of mandarins for about two months.

“It had all the qualities you want in a mandarin — easy to peel, rich color, great flavor, and very low seeded even when grown near other varieties,” Roose said. “That combination is very rare.”

Williams takes pride in the legacy he and Roose helped build.

“You spend years working with hundreds of trees, and then one day there it is — the one that checks all the boxes,” he said. “When you see it in grocery stores and lunchboxes around the world, that’s a pretty good feeling.”

The Tango is part of a citrus innovation legacy that began in 1907 when the UC Citrus Experiment Station opened on what is now the UCR campus. UCR has since introduced more than 40 new citrus varieties, including the sweet-tasting Oroblanco grapefruit, which is now grown as a specialty crop worldwide.

UCR is also home to the Givaudan Citrus Variety Collection, which has approximately 4,500 trees representing more than 1,000 different varieties of citrus and citrus relatives from growers worldwide, preserving citrus biodiversity for decades to come.

“When you look at Tango’s success, it’s gratifying — but it also reminds you that we’re just one chapter in a much longer story of citrus improvement at UCR,” Williams said.

“The challenges facing citrus today — new diseases, climate, sustainability — are different from those a century ago, but the mission is the same: to keep California citrus viable, valuable, and accessible well into the future.”

**Header Image: **UCR’s Timothy Williams, left, and Mikeal Roose, developed the Tango mandarin variety. (UCR/Stan Lim)