Three new varieties of tangerines - the TDE2, TDE3, and TDE4 - are the University of California's most recent citrus varieties to be released for commercial production. The tangerines, which are complex hybrids, are siblings since they share the same parents. The varieties will be patented and eventually be given trademarked names. The three tangerines are large fruited compared to other varieties, have a sweet taste, and bear fruit with a deep orange rind.
"While the new tangerines share many similarities, they also differ from each other in their characteristics," said Mikeal Roose, professor of genetics at UC Riverside. "They do have one outstanding attribute however: all three are very low seeded, less than one seed per fruit, even when the trees are planted with other varieties. This is a highly-sought attribute for the fresh fruit market."
Although the crosses were made in 1973, it was not until the 1980s that now-retired UC Riverside Professors Robert K. Soost and James W. Cameron recognized the potential of these individual seedlings for commercial development.
Each seedling produced from a cross between two citrus varieties has a unique genetic makeup. "You can think of citrus genetics as similar to human genetics," said Roose, who was assisted in developing the new tangerines by UC Riverside staff scientist Tim Williams. "When you cross a mother and a father, the children may have some similarities but they are different from one another."
The TDE2, TDE3, and TDE4 are now being released for commercialization in California under non-exclusive licensing agreements with the University of California. Licensed growers and wholesale nurseries in California can obtain budwood, propagate the varieties and freely market the resulting trees and fruit. The University of California does not produce trees for sale to the public. It will take a year or two before trees become available for planting, and another two or three years before the young trees produce much fruit.
"The tangerines also hold very well on the trees," said Roose. "In Riverside, the TDE2 is good-tasting when picked from the tree anytime between February and May; the TDE3 is good-tasting when picked from the tree anytime between January and March; for the TDE4, the range is February to April."
There are, however, some unknowns associated with the new tangerines. For example, it is not clear how well the trees will yield when isolated from other citrus plants. "Some citrus require pollination or need stimuli like plant hormone sprays to set good crops," said Roose. "We hope to find out in the next two years how our new varieties perform." Like many tangerines, the new varieties also have 'alternate bearing' - a big crop one year followed by a much lower yield the next year(s). When the crops are very light, fruit size tends to get large and the rind gets rough and bumpy, Roose noted.
"The three new varieties are also quite thorny," said Roose. "This is a common characteristic of new hybrids. Moreover, the tree size for all three varieties is large for tangerines. All three new varieties grow more like orange trees, we've found." Characteristics of fruit of the three new varieties are listed in Table 1.
| Average fruit size |
for a tangerine
|Mean width||2.95 in (75 mm)||2.60 in (66 mm)||2.95 in (75 mm)|
|Mean height||2.32 in (59 mm)||2.20 in (56 mm)||2.30 in (58 mm)|
|Mean weight||6.5 oz (185 g)||4.75 oz (135 g)||6.0 oz (175 g)|
|Avg. juice content||49||48||42|
Table 1. Characteristics of the TDE2, the TDE3, and the TDE4. All three tangerines have an attractive deep orange rind color, have a rich fruit flavor and are marked by the virtual absence of seeds even in mixed plantings.
"We are very excited about the new tangerines," said Roose. "Besides having considerable potential as commercial varieties, all three should be of great interest to backyard citrus growers looking to add interesting new tangerines to their collections."
UC Riverside 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 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 UC Riverside agricultural research.
UC Riverside 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.