This is just what you've been waiting for! According to Siebert et al (2010): "Tango is a patented (Plant Patent #17863) irradiated selection of W. Murcott mandarin developed at UC Riverside. Fruit of 'Tango' are similar to W. Murcott in all appearance, quality and production characteristics with the exception of seed numbers. 'Tango' fruit are deeply oblate in shape with no neck. The fruit is medium sized for a mandarin (classed as Large by State of California standards and size 28 by industry packing standards) averaging 59 mm (2.32 in.) in diameter and 48 mm (1.89 in.) in height with a very smooth, deep orange rind color. The rind is relatively thin and at maturity is easy to peel. The fruit interior has fine flesh texture with 9-10 segments and a semi-hollow axis of medium size at maturity. The fruit are juicy averaging slightly over 50% juice with an average weight of 90.6 g (3.2 oz.). 'Tango' matures in winter (late January) and holds its fruit quality characteristics through April into May. Production is excellent averaging 800-900 cartons/acre when planted at densities of 250-300 trees/acre. Fruit from trees on Carrizo and C-35 citrange rootstocks average 11.1-13.1% soluble solids and 0.97-1.19% acid in January increasing to 13.5-15.4% soluble solids with decreasing acid of 0.54-0.82% in April. 'Tango' averages 0.04 + 0.2 seeds per fruit in the presence of cross-pollination at seven trial locations throughout California compared to 11.6-22.6 seeds per fruit for W. Murcott. Pollen of 'Tango' has very low viability consequently it has a very low likelihood of causing seeds in other citrus, particularly mandarins, when planted nearby. Like 'W. Murcott', trees of 'Tango' have a tendency to overbear and therefore need to be regularly pruned to maintain good, but not excessive production and to maintain fruit size and prevent alternate bearing. Crop yields should be limited to about 150-170 lbs/tree (6-7 mandarin boxes) through a combination of pruning and, if needed, fruit thinning and should be harvested on time, not left on the trees as this can lead to alternate bearing (information from M.L Roose and T.E. Williams). Patent and/or propagation rights for 'Tango' Mandarin are held by the Regents of the University of California. Budwood is available only to nurserymen who have a License Agreement for these cultivars."
More information is available from the developer's website, the Citrus Variety Collection website, the Citrus Clonal Protection Program website, and the plant patent description.
Enjoy! (RR Krueger, 07/15/2010)