On a FasTrack
Fruit breeders have a clever new tool to speed up the process.
Horticulturist Ralph Scorza pollinates plum flowers while geneticist Ann Callahan measures sugar content and molecular biologist Chris Dardick measures fruit size. FasTrack allows scientists to pollinate flowers and evaluate fruit from the same plants in the greenhouse year round.
FasTrack is the name of a new plant breeding process developed by U.S. Department of Agriculture researchers. It uses genetic engineering technology to greatly speed up the breeding process, but the final products are not Genetically Modified Organisms.
The exotic gene that lends speed to the process is removed in the final stage of the breeding process.
FasTrack was created by a research team at the Appalachian Fruit Research Station in Kearneysville, West Virginia. Led by horticulturist Dr. Ralph Scorza, it includes plant physiologist and tissue culture specialist Dr. Chinnathambi Srinivasan, geneticist Dr. Ann Callahan, and molecular biologist Dr. Christopher Dardick.
It’s now being used primarily in plum breeding, but could be adapted to other plants, and is most valuable in tree fruits where the breeding process takes so long.
In an interview with Good Fruit Grower, Scorza said that “FasTrack doesn’t change what plant breeders want to do, it just allows them to do it faster.” That’s important to Scorza, who has spent decades breeding peaches and plums, a very slow process. What has previously taken 15 to 20 years can, using FasTrack, be done in five to ten years, he said. “This is a very powerful technology.”
The key to FasTrack is a gene named PtFT1, often referred to as the ECF gene—ECF standing for early and continual flowering. That gene, which is present in many plants, was taken from a California poplar tree and inserted into the plum cultivar BlueByrd. Srinivasan produced 196 transgenic plum plants that are bushlike shrubs that produce flowers continually, like tomatoes. Flowers and fruit at various stages of maturity are on the bush at the same time, often in the first year.
“In our breeding work now, we are tied to a season,” Scorza said. “We work like crazy in a short window in spring to make our crosses, and then hope frost doesn’t wipe them out. Then we plant the seeds and wait three to six years to see the fruit.
“With trees that are always flowering, we can make crosses any time. We never have to stop. It just makes it go so much faster.” The plants are being grown in greenhouses, so work can go on year round. These plants also do not require a dormant, or chilling, period.
The transgenic trees can be crossed with normal trees that have disease resistance, sweetness, and other desirable fruit quality traits. But the trees will bear mature fruit in one year, allowing early evaluation of fruit quality.
The transgenic plants are themselves not suitable for orchard production—although they might be of interest to growers using high tunnels, to home gardeners, to growers in the tropics, or to people growing houseplants.
In the final step of the breeding process, the trees that will be selected for use as commercial cultivars won’t carry the ECF gene, will flower normally, and will be no different than trees produced by traditional breeding processes.
FasTrack, Scorza said, meshes well with other new breeding tools. By identifying molecular markers, for example, breeders can determine whether plants carry desirable traits without waiting for fruit to develop. Those that don’t can be weeded out early, reducing the amount of space devoted to seedlings in test plantings. But the fruit still has to be tasted—the proof of the pudding. Without FasTrack, after using markers, it still takes three to six years to see fruit, compared with one year for FasTrack.
Scorza sees lots of reasons why speed is important in plant breeding. He believes the American stone fruit industry is vulnerable, especially to plum pox, which has devastated the industry in Europe. More and more, there are threats from invasive diseases and insects, for which we have no defense, and climate change is also putting stress on existing fruit varieties, he said.
“We can’t wait 20 or 30 years,” he said.
Scorza developed the plum variety HoneySweet, which is immune to plum pox, but it contains a gene from the plum pox virus itself that was introduced using genetic engineering techniques. While it has been approved for planting by several U.S. government agencies, growers haven’t planted it since, up to now, plum pox virus has not spread in the United States.
Scorza is particularly concerned about the California dried plum industry. It produces 99 percent of America’s dried plums and 60 percent of all the dried plums in the world. Yet the industry is based on one cultivar, Improved French, making it vulnerable to disease and pest outbreaks.
Should plum pox ever come to America and not be contained by quarantine and eradication of infected trees—as was done in Pennsylvania, Michigan, and New York—the industry might need to turn to HoneySweet as a parent for new resistant cultivars. Scorza believes the variety he created would be called on in such an emergency.
Meanwhile, the Kearneysville scientists are using FasTrack to improve trait quality for the California dried plum industry. They are working on a five-year project that started in September 2009, collaborating with University of California pomologist and extension specialist Theodore DeJong.
According to information on the university’s Web site, “more than 10 different lines of plum tree have set fruit within the first 14 months of growth. These trees are continually flowering, and several rounds of pollination have produced fruits at different stages of maturity—with flowers, immature fruit, and mature fruit on the same plant.”
Dr. Albert Abbott, who works with molecular markers at Clemson University, is part of the project, as is Dr. Jayson Harper, an agricultural economist at Penn State.