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Gene Gun Speeds Search for New Orchid Colors

Hank Becker and Maria Bynum

A corn gene is giving U.S. Department of Agriculture researchers a jump start in verifying what the color of a new flower will be.

"If orchid plants are bred for a new color, it's anyone's guess about the outcome. Usually, the plant industry now waits three years until a bloom appears," said Robert J. Griesbach, a plant geneticist with USDA's Agricultural Research Service.

"We found a corn gene that will give us results on the color of new hybrids in just three days," he said. That gene regulates the pigment in corn plants.

Griesbach said the genetic technique - coating the corn DNA on microscopic gold pellets that are propelled, by a particle gun, into orchid flower petals - screens for genetic flaws in the parent plants crossed to breed new hybrids.

"That should give plant breeders a higher degree of certainty in crossing various orchid colors like purple and yellow by cutting down on the number of unwanted color mutations," he said. About one in a thousand orchid plants lacks adequate pigments, causing white or near white flowers. Other mutations result in flowers that have varying degrees of purple pigment, ranging to about 25 percent of true purple color.

"We have tested the technique successfully on bulb plants like gladiolas and other ornamentals like petunias, as well as on orchids," said Griesbach, an expert on flower pigmentation.

"Genetic screening could result in a broader range of colors in orchids and other ornamental plants."

Griesbach said the technique could be "a boon to breeders of orchids because of the flower's long generation time - up to six years in some commercial types." Orchid flowers are highly prized, he added, noting that potted phalaenopsis orchids are "fast becoming a major economic crop."

Griesbach tried the faster genetic technique after removing white petals from orchid flowers (Doritis pulcherrima Lindl.). He bombarded the petals with microscopic (1-mm diameter) gold pellets coated with DNA taken from corn plants. DNA was obtained from T.M. Klein of E.I. DuPont, Glascow, Del.

"Screening plants for color mutations is a new use for the particle gun that Bob Griesbach demonstrated for the first time," said Roger Lawson, National Arboretum, Washington, D.C. "The gold pellets were more than 10 times smaller than the dot at the end of this sentence," he said.

Over more than two years of tests, Griesbach found that the introduced corn genes causes near-white flowers to gain pigment within 48 hours. On fully colored, wild-type flowers, the purple continued to develop for the next 24 hours.

"Eventually, the orchid cells with the corn genes looked the same as the purple cells found in wild plants, without loss of pigment," Griesbach said.

For details, contact: Robert J. Griesbach, Floral and Nursery Plants Research Unit, U.S. National Arboretum, Agricultural Research Service, USDA, Beltsville, MD, (301) 504-6574.

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