Tango, an irradiated, seedless version of the popular W. Murcott (Afourer) mandarin, has been released by the University of California’s Citrus Breeding Program.

The mid- to late-season, easy-to-peel W. Murcott has a global reputation for high quality. It has been widely planted in California, particularly near Bakersfield and Madera, during the past decade, with an estimated 2 to 3 million trees planted, more than half of them bearing.

W. Murcott, distinct from the Murcott also known as Honey in Florida and Arizona, has excellent production with little alternate bearing, and, provided it is isolated from other citrus, it produces seedless fruit.

But in California, where isolated commercial citrus orchards are becoming increasingly rare, many W. Murcott groves have developed seedy, lower-value fruit caused by cross-pollination by other mandarins, Valencia oranges, Minneola tangelos, lemons and other citrus.

The Tango was highlighted in a talk on new varieties by Tracy Kahn, principal museum scientist for the Citrus Variety Collection at UC, Riverside, during a recent citrus day at Tulare, Calif.

Kahn, who conducted field evaluations of Tango at Lindcove and Riverside, explained it was developed as a solution to the W. Murcott seed problem. Tango does not have seeds because it does not produce viable pollen.

The new mandarin, developed by geneticists Mikeal Roose and Tim Williams of the Citrus Breeding Program at UC, Riverside, was the most promising of several W. Murcott selections irradiated to induce mutations for reduced seed counts.

Tango was planted in replicated trials at seven locations in the state, including three fruiting trials planted in 2001 and 2002 and four trials planted in 2003 and 2004 that will bear in 2007.

Fruit sampled this year in locations where cross-pollination occurs showed an average of less than 0.2 seeds per fruit, while W. Murcott trees used as a check averaged 8 to 15 seeds per fruit, Kahn said.

At Riverside, Tango matures in late January and holds fruit quality characteristics through April. It has similar tree and fruit traits to W. Murcott except seediness, although this year Tango fruit had lower acidity than W. Murcott.

Fruit size is moderate at about 2.3 inches and 3.2 ounces, shape is oblate with a deep orange color, and the rind is easily peeled. The flesh is also deep orange colored and has a 12 percent to 14 percent Brix when mature.

Tree growth is upright and production begins the second year after planting. Alternate bearing does not appear to be a significant problem.

Since Tango is from mutation breeding, its genetic stability may be an issue, although more than 60 trees propagated from multiple generations of Tango buds have remained true to type.

The Citrus Breeding Program has received patent-pending protection for Tango. Citrus nurseries licensed by the California Department of Food and Agriculture may purchase a license to propagate the new variety.

Among Kahn’s 2005 citrus studies are solids-to-acid ratio evaluations of a group of satsuma varieties, mostly foreign in origin, compared to industry standards Frost Owari, Okitsu Wase and Kuna Wase.

China S-2 and China S-9, reported to have cold hardiness, were imported from Hubai Province in China. Aoshima is an Owari selection and one of the leading late-maturing varieties in Japan. China No. 6 and China No. 7 are two other cold hardy varieties from Hubai Province.

Iveriya comes from the former Soviet Republic of Georgia. Silverhill is a nucellar seedling selection of Owari made by W. T. Swingle in about 1908. Xie Shan is a Chinese variety said to ripen extremely early compared to other varieties grown in China.

Miho Wase is a sister nucellar seedling to Okitsu Wase in Japan. Armstrong is from a selection made at the Louisiana State University Research Station. Miyagawa is a limb sport of Zairai selected in Japan in 1923.

Kahn said those meeting the legal maturity standard for solids-to-acid of 6.5:1 at Lindcove as of Oct. 6, 2005, were Okitsu Wase, China S-9, Xie Shan, Miho Wase, Armstrong, and Miyagawa.

Those with soluble solids above 9 at Lindcove were Frost Owar, Okitsu Wase, Kuno Wase, and Miho. Miyagawa was the sole variety with percentage acidity below 1.0 at Lindcove in early October.

Kahn said all the varieties were found to be above the legal maturity solids-to-acid level by Oct. 20, 2005.

Anil Shrestha, IPM weed ecologist at the UC Kearney Agricultural Center at Parlier, urged growers to manage weed pests wisely to help limit the weed seed bank in the soil.