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 62^nd 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.

Fairchild LS

Also a UCR breeding product is the Fairchild LS, an irradiated selection of the Fairchild mandarin. The size 24 fruit averages 2.4 seeds each, matures in January, and holds well on the tree into April. Yields average 45 tons/hectare. The brix-acid level in February is about 12:1.

“The Fairchild SL needs a cross pollinator for the best yields,” Kahn said. The variety is alternate bearing yet controllable.

A mandarin variety with roots in the USDA citrus breeding program in Florida is called USDA 88-2. The fruit is a hybrid cross from the Lee mandarin and Nova tangor. The early-maturing fruit retains low seeding under all cross pollination conditions, Kahn says.

USDA 88-2 has a distinctive rich flavor and yields can be erratic. The brix-acid level is 15:1 to 16:1. The fruit can develop a slightly bulging navel.

Kahn is also evaluating about 20 new Satsuma mandarin varieties plus new Clementine selections. The most commercially-planted Clementine in California is the Clemenules (Nules) Clementine.

The CVC is evaluating the Spanish-patented varieties Hernandina Clementine and Arrufatina Clementine and others for possible Western commercial production.

The Red Nules (Top Mandarin Seedless), developed in Italy and Sicily, is a hybrid between Nules Clementine and Tarocco blood orange and is a proprietary variety. The flesh can have red streaks or pigmentation across the entire surface, but without the intensity of the Moro blood orange. The harvest window in the San Joaquin Valley is January through February.

Turning to lemon varieties, Kahn and Glenn Wright, University of Arizona citrus specialist, are in the second year of yield evaluations on 12 selections in CVARS trials. The goal is to provide lemon growers with crucial information on tree growth, yield, packout, and fruit quality characteristics.

The Walker Lisbon and Femminello Santa Teresa selections have produced the highest yields, Kahn said, followed by Corona Foothills and Limonero Fino 49.

“These selections so far exhibit precocity, good yield, and large fruit,” Kahn said. “These could be good alternatives to currently planted selections in desert production.”

In UCR evaluations on limes, the CVC has released a version of the popular Australian finger lime variety for propagation. Nicknamed the “caviar lime,” the Australian variety has dense foliage with heavy thorns. The best harvest method is to shake the fruit onto a tarp. Harvest occurs year round with December and January the best months. The fruit rind is greenish black to dark purple in color.

For more information on CVC studies and findings, go online to www.citrusvariety.ucr.edu.

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