Yearning To Be Free Of Seeds
Maricopa, California – Last April, California’s largest citrus grower threatened to sue beekeepers, accusing them of letting their insects “trespass” on mandarin groves.
The growers were not afraid of being stung, they were afraid that the bees would pollinate their trees, something farmers usually want bees to do. But these trees in the San Joaquin Valley were planted to bear seedless fruit, and pollination would create seeds.
This spring, a citrus growers trade association will be lobbying the state legislature for a Seedless Mandarin Protection Act that would establish “no-fly zones” of three kilometers for hives around designated orchards.
If the response seems unusual it’s because of what is at stake: seedless mandarins fetch three to four times the price of seeded ones, according to a 2005 study. The acres in California planted with mandarins, mostly seedless varieties, have grown to 27,000 from 10,000 in 1998. In 10 years it will probably be hard to find mandarins, also known as tangerines, with seeds.
“It’s becoming impossible to market mandarins with a high level of seeds,” said Etienne Rabe, a manager for Sun Pacific, a large grower.
In the 1960s, California researchers discovered that by applying a spray at bloom, simulating the growth hormones naturally secreted by seeds, farmers could obtain good harvests of seedless clementines. Bees became undesirable.
Spanish scientists improved this technique, and in the 1980s and 1990s, seedless Spanish clementines conquered markets in Europe and the eastern United States.
California growers saw this success, and in the late 1990s rushed to plant clementines. mostly in the San Joaquin Valley citrus ,belt, from south of Bakersfield to Fresno.
They also placed big bets on a Clementine like variety of seedless mandarin, found in Morocco in the 1980s, with the ungainly name of W. Murcott Afourer. “As shipments of mandarins soar in the next few years, “there’s going to be a head-on clash” with Spanish exporters,” Mr. Rabe said.
A partial solution for this problem – an irradiated version of W. Murcott that never develops seeds, even when cross-pollinated by bees – has been developed by Mikeal L. Roose and Tim Williams, citrus breeders at the University of California at Riverside. In 1996 they irradiated W. Murcott budwood sticks (stems used for grafting to rearrange the chromosomes to cause sterility.
Dr. Roose and Mr. Williams have undertaken a far-reaching program trying “to rid the seeds from 63 varieties of citrus. Man,, researchers around the world are irradiating citrus.
Scientists also are breeding new seedless varieties, mainly by hybridizing trees with three sets of chromosomes, rather than the normal two. That genetic imbalance causes the fruits to be seedless.
An experimental method called cybridization transfers a gene for sterility into seedy varieties.
The success of all these methods may show that, paradoxically, the best way for a mandarin to proliferate is to be sterile.