Citrus Breeding Building On Knowledge
December 1, 2007 “Swingle was a clear pioneer in terms of citrus breeding,” says Fred Gmitter, citrus breeder/horticulturist at the Citrus Research And Education Center (CREC) in Lake Alfred. “His first objective after the disastrous freezes of the 1890s was to introduce cold hardiness from the trifoliate orange into sweet orange and grapefruit, among other cold-susceptible citrus. It was a good idea, but it also transmitted terrible fruit quality. But, from that miscalculation came Carrizo citrange and Swingle citrumelo, the most widespread rootstocks in Florida today.”
CREC Steps Up
The CREC breeding program was expanded greatly in 1984 and 1985 when Jude Grosser and Gmitter were hired to conduct citrus genetic improvement research. They were teamed with Dr. Bill Castle, an outstanding field horticulturist, and Dr. Gloria Moore, a molecular biologist, to work cooperatively, using all forms of genetic manipulations to develop new varieties for the future of the Florida citrus industry.
Genetics And Breeding
According to Gmitter, future breeding will be defined by the expanding horizons of genetic research. He adds that genetics could lead to breakthroughs in the battle against citrus canker and greening.
“Breeding in the traditional sense of making crosses and selecting offspring will have little impact directly on canker and greening, aside from rootstock contributions,” he says. “However, molecular breeding, that is the identification of genes for resistance and their introduction to commercial citrus through genetic engineering, has great potential to address these serious disease problems, as well as our old enemy, citrus tristeza virus (CTV). Researchers are exploring many avenues to find and utilize genes for resistance against these three diseases. Within 10 years, it may be possible to see the first of these resistant trees in citrus groves in Florida.
“If there is a genetic resistance solution, most of the major disease problems will be addressed through genetic engineering. What most people do not recognize is that all grapefruit and sweet orange varieties have originated by chance mutations, so breeding in the traditional sense is impractical for these fruit. Even if we could cross the disease resistance genes into them, and we can, the fruit produced on such resistant hybrids would not look like orange or grapefruit.”
Through traditional and genetic breeding, Gmitter says new rootstocks will be developed that may help Florida growers manage the risks associated with greening, along with many other challenges like diaprepes, CTV, blight, and, calcareous soils.
Future Vision
Gmitter reflects on what will be enabled in breeding by technology over the next decades, noting the important role of genomics.
“Well, after I discover the Fountain of Youth, I’ll continue breeding citrus the way we do now, but with technological advances, making the breeding process much more precise and efficient,” he says. “It is for this reason that scientists are so excited about genomics, because it will open a whole new toolbox for use in achieving genetic goals.”
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