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New Citrus Variety Released by UCR

New Citrus Variety Released by UCR

(October 23, 1999)

Gold Nugget - a seedless, sweet tangerine with an extraordinarily long harvest season - will become the first new University of California, Riverside citrus variety to be released for commercial production since the mid-1980s.

Availability of budwood from which to propagate trees bearing the new tangerine was announced this week in a letter from the University of California to commercial growers and wholesale nurseries. Plant material will be available to growers and nurseries through a licensing agreement with the university.

More than 30 years in the making, the new tangerine - also known as a mandarin - received its descriptive name from its bright orange, slightly bumpy rind. But Gold Nugget is particularly regarded for its rich, sweet flavor. Additionally, it is seedless, a highly-sought attribute for the fresh fruit market.

"It also holds very well on the tree," said Mikeal Roose, a UCR professor of genetics who since 1986 has directed continued development of the Gold Nugget variety. "In Riverside, the fruit is good-tasting when picked from the tree anytime between February and May or June."

UCR scientists have a long tradition in citrus research. In 1907, the University of California established the Citrus Experiment Station in Riverside to support Southern California's growing citrus industry with scientific data to improve production. In 1917, the station moved to its present site, which would also become a new University of California campus in 1954.

Now known as the Citrus Research Center-Agricultural Experiment Station, the work of the UCR center has grown to include all aspects of agricultural production in arid and semi-arid subtropical lands. Research on citrus production and development of new varieties remains a major focus of UCR agricultural research.

UCR is also home to the University of California Citrus Variety Collection of some 900 varieties that have been used extensively to solve citrus disease problems and improve commercial varieties. Development of Gold Nugget was preceded by a number of UCR- developed citrus varieties, including the grapefruit varieties known as Oroblanco and Melogold, patented by the university in 1981 and 1986, respectively.

Gold Nugget is a cross between two tangerines -- Wilking and Kincy -- non-commercial varieties also developed at UCR. Although the cross was made in the 1950s, it was not until 1975 that now-retired UCR Professors Robert K. Soost and James W. Cameron "selected" the individual seedling that showed the greatest promise for commercial development.

Each seedling from a cross between two citrus varieties has a unique genetic makeup. "You can think of citrus genetics being like human genetics," said Roose, who was assisted in developing Gold Nugget by UCR staff scientists Tim Williams and Ricki Kupper. "When you cross a mother and a father, each of the children are different."

The selected tree was repropagated and trees planted in Riverside for additional evaluation. Certified virus-free budwood trees were established by UCR Professor David Gumpf at the Citrus Clonal Protection Program in Riverside in 1986 with virus-free trees later being established at the Lindcove Research and Extension Center near Visalia.

Field trials began in 1993, with growers around the state agreeing to plant trees in actual commercial crop settings so that UCR scientists could evaluate how the new variety grows in a range of climates and under a variety of farming practices. Roose said scientists were also interested to see how susceptible the trees would be to disease and insect pests and how long it took trees to reach fruit-bearing maturity.

Following three years of fruit data from the field trials, Gold Nugget is now being released for commercialization under licensing agreements with the University of California. Growers and wholesale nurseries that sign licensing agreements can propagate the variety and market the resulting trees and fruit, Roose said.

Still, it will likely be several years before fruit becomes commercially available, since it takes about three years before propagated trees are mature enough to produce fruit, he said. And, it is yet to be seen if commercial growers will see enough commercial potential -- either in the U.S. or in overseas markets -- to plant orchards of Gold Nugget.

With a developing mandarin market in California, there may be interest among commercial growers in marketing the new variety. Gold Nugget, being a later-season mandarin, may complement the existing mandarins that are available in December and January, Roose said. And, the popularity of mandarins in European and Asian countries may interest growers looking to expand their export markets, he said.

Roose said the variety should be of great interest to backyard citrus growers looking to add an interesting new mandarin variety to their collections. "I think it will succeed as a backyard fruit," he said.

The University of California, Riverside ( is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment has exceeded 21,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion.

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