Tracy Kahn has her eyes peeled for good citrus varieties for Western growers to help them economically compete in the ever changing world market.

Kahn is the curator of the University of California, Riverside (UCR) Citrus Variety Collection (CVC) in Riverside. The CVC has two trees each of more than 1,000 citrus types, one of the premier citrus germplasm collections in the world.

Kahn’s work includes the evaluation of new varieties in California, the nation’s second largest citrus-producing state behind Florida. California citrus bearing acreage totals about 277,000 acres, according to the 2010 California Citrus Acreage report from the National Agricultural Statistics Service.

Nearly two-thirds of California’s citrus acreage is planted in sweet oranges and related hybrids (Navel, Valencia, and others) with a slight decrease in bearing acreage since 2008. Lemon acreage stands at 16 percent; also with a slight acreage reduction since 2008.

Mandarin production is about 14 percent of total citrus acreage with significant gains in bearing and total acreage. Grapefruit, pummelos, and other citrus types comprise about 4 percent.

“The desire for seedless fruit continues to increase especially for the large-scale commercial citrus market,” said Kahn, the opening speaker during the 62nd annual National Citrus Institute meeting in San Bernardino, Calif., in November.

Kahn says mandarin and tangerine varieties are highly sought by consumers, including Clementine, W. Murcott, Tango, Minneola, and others. Consumers desire easy-to-peel, brightly-colored fruit with good flavor.

Mandarin shippers want a brix-acid ratio of greater than 10:1, Kahn says, compared to the legal standard of 6.5:1.

New scion varieties for Western commercial production basically have three sources: the UCR breeding program; introductions from outside California approved by the California Citrus Clonal Protection Program (selections from the University of Florida and USDA breeding programs for example); and from existing varieties and selections from collections.

“The Tango variety is having the most impact in California right now,” Kahn says.

Tango, an irradiated, low-seed version of the popular W. Murcott mandarin released for commercial production in 2006, was developed by Mikeal Roose and Tim Williams of the UCR Citrus Breeding Program. The Tango averages .2 seeds per fruit in mixed plantings with good quality fruit and yields.

About 2 million Tango trees are planted in California, Kahn estimates. Increasing international demand for low-seed citrus is largely behind increased Tango plantings. The first significant Tango harvest is underway this winter.

Another mandarin variety gaining popularity is Daisy SL. The compact-size tree was released about a year ago by Roose and Williams. The mid-season selection is harvested from November to February. Daisy SL features a 13:1 to 14:1 brix-acid ratio, gains optimal flavor by mid-January, and averages 2.2 seeds/fruit.   

“Daisy SL is a large-sized mandarin with a smooth, thin, deep-orange rind with excellent rich flavor,” Kahn said.

Daisy SL yields average 60 to 100 pounds per tree annually in four-year-old trees. Up to 20 percent fruit splitting can occur in some years. The fruit holds well on the tree for about eight weeks. Trees require pruning to manage the crop.

During the 2009‐10 season, 10 of 83 Daisy SL trees in trials produced some fruit with high seed content (10‐15 seeds/fruit) compared to the standard Daisy variety. Most trees with seedy fruit had only a few such fruit. The total percentage of seedy fruit (more than six seeds/fruit) was about 1 to 2 percent overall with most found at the Coachella Valley Agricultural Research Station (CVARS) in Thermal, Calif.