Kevin Bouffard

With its only other experimental grove ravaged by citrus greening, the U.S.
Department of Agriculture depends exclusively on this 500-acre farm near
Leesburg to develop the new trees that will determine the future of Florida
citrus.

"This is a crucial resource for our breeding program," said Ed Stover, the
leader of the Horticulture and Breeding Research Unit at the USDA's
Horticulture Research Laboratory in Fort Pierce, on Wednesday.

Stover was addressing the annual meeting of the board of trustees for the
Florida Citrus Research Foundation, which owns and oversees the 48-year-old
A.H. Whitmore Farm that the USDA lab uses to test new citrus tree hybrids
under actual Florida growing conditions.

If the hybrids prove successful here, the USDA releases a limited number of
the new trees to growers in other parts of the state as a further test of
viability. When the new trees show viability in other parts of the state,
the hybrids are made available to all commercial growers.

The USDA lab had also used its Picos Farm in Fort Pierce as a new hybrid
proving ground, but that's no longer possible because it is overrun with
citrus greening, a fatal bacterial disease, Stover said. The Picos Farm is
being used only to test new hybrids for their ability to resist a greening
infection.

While developing greening-resistant trees has become a top priority, the
USDA needs the Whitmore Farm to develop new hybrids with other desireable
qualities, such as seedless, easy peeling, flavor and resistance to other
diseases, such as the citrus tristeza virus, said Kim Bowman, the lab's
research geniticist working on new tree rootstocks.

A commercial citrus tree consists of a rootstock, which grows mostly below
ground and is tailored to local soil and weather conditions. Another
variety, called a scion, is grafted onto the rootstock and produces the
fruit.

The Whitmore Farm has produced four new rootstocks during the past decade
with another ready for release in the next year, Bowman said. The new
rootstocks have been shown to produce more fruit than traditional ones.

Earlier this year, Bowman and his team began experimenting with genetically
transforming the four new rootstocks to introduce genes that may be
resistant to greening, he said. They should know by next year whether the 50
new "transgenic" hybrids resist greening infection.

Genetic transformation involves taking genes from other organisms and
splicing them into the citrus tree's DNA to create a new hybrid.

Gregory McCollum, a research plant physiologist, told the board he is using
the same genetic transfomation techniques to search for greening-resistant
scions. He is working with genes introduced into tomato and tobacco plants
that are susceptible to a bacteria similar to the one that causes greening.

The tomato and tobacco plants are easier to work with and should find a
greening-resistant gene more quickly, he said. The technique is similar to
using mice as an early indicator to test new drugs for humans.
www.checkbiotech.org