Based on their proximity to large Eastern urban areas, Southern growers of muscadine grapes could probably capitalize on fresh-market demand if not for the variety’s seediness and short shelf life.
But Dennis Gray, a professor of developmental biology at the University of Florida’s Mid-Florida Research and Education Center in Apopka, is leading a research team that hopes to address those constraints with seedless, disease-resistant muscadine varieties.
“We think if we could get something that would sit on shelves and especially be seedless, people outside of the Southeast would be seeing something else they hadn’t seen,” he says.
Jeanne Burgess, vice president of wine making at Lakeridge Winery and Vineyards in Clermont, has followed Gray’s research for years.
Although the winery grows muscadines purely for juice and wine, she says his work—if successful—would be a boon to the entire Florida grape industry.
“We think it would really benefit the fresh fruit portion of this industry in the Southeast and would pump it up,” Burgess says.
Southerners are familiar with muscadines and understand that they have seeds. But she says most consumers elsewhere are turned off by muscadine’s seediness.
“It would open up new markets,” she says of a seedless muscadine. [People elsewhere] like grapes, and the flavor of the muscadine is very engaging—it’s almost like a tropical fruit for people who are not familiar with it.”
A multi-state effort
Gray’s work is being funded in part by a five-year, $2.2 million specialty crop grant from the U.S. Department of Agriculture’s National institute of Food and Agriculture.
Other members of the team include researchers from the University of Georgia, the University of Tennessee, the USDA’s Agricultural Research Service in Poplarville, Miss., and the University of the Virgin Islands.
Gray and his team are using what he calls precision breeding—or cisgenics—to transfer genes targeted for their desirable traits from other grape varieties into muscadines.
Conventional breeding involves trading genetic material between two plants through crosses. But the results are unpredictable, Gray says.
Since cisgenics involves only sharing a small amount of genetic material with a known trait, the results are much more precise, Gray says.
And because his work only involves sharing genetic material among grape varieties, Gray says he’s hopeful that the U.S. Department of Agriculture and the Environmental Protection Agency will not regulate the resulting grapevines.
Through gene sequencing, scientists have created a genetic roadmap of the grape.
Molecular biologists, such as Zhijian Li, then must identify promoters—snippets of DNA that control the expression of a genetic trait.
Already, he has a three-page list of promoters.
"We found we didn’t know how many promoters there were,” Li says.
Gray and his team also are using marker-assisted breeding. They attach a small piece of benign genetic material to the desired trait, such as a gene that regulates anthocyanin production in plants.
Because the anthocyanin gene causes production of a natural reddish pigment, breeders can quickly tell whether the desired trait that’s attached to the marker gene was transferred.
Growing vines in the lab
Once they have what they think is the correct genetic mix, technicians will then use tissue culture to propagate plants.
Tissue culture involves exposing a small clump of plant cells to various nutrient broths that contain specific plant growth hormones.
One hormone, for example, may promote root development, whereas another will promote leaf formation.
All of this is done under nearly sterile conditions, resulting in plants that are disease-free.
After the tissue culture begins to resemble a grapevine, technicians transplant it to potting medium and place it in a greenhouse.
The entire process has taken Gray and his team several years to perfect, and the University of Florida holds several patents on it.
Eventually, the vines are moved to the field for evaluation of agronomic characteristics and fruit quality. Once his lab gets revved up, Gray says it could take as little as one year from tissue culture to vines in the field.
In addition to plots at the IFAS center in Apopka, the new vines also will be put into plots in the Virgin Islands and into an existing variety evaluation trial in Poplarville overseen by Stephen Stringer, an ARS research geneticist.
“We’ll be able to tell even with a small number of plants how they’ll perform against the varieties that are already growing there,” Gray says. “Steve has a lot of experience and feel for the crop, and there’s a lot of experience that comes into evaluating these things.”
Gray and his team use Thompson seedless as what he calls their laboratory “white mouse”—or test animal—because of its acceptance to precision breeding and tissue culture.
If a trait can be transferred to Thompson seedless, the team tries it next on muscadines, which are more temperamental, and other varieties.
So far, Gray says he’s successfully transferred the gene for powdery mildew resistance from chardonnay into Thompson seedless.
The resulting plant isn’t immune from powdery mildew. Instead, precision breeding gives the vines seven to 10 additional days before mildew infection incurs. This could potentially reduce the number of fungicide treatments growers applied during a season.
\n addition, sour-bunch rot was reduced by 42 percent compared with the control, and black rot infection was cut in half.
Benefits beyond muscadines
Eventually, Gray says he’d like to use precision breeding to impart seedlessness and disease-resistance to the Delicious muscadine variety, a University of Florida release.\
Not only does Delicious have excellent yield and eating quality, but it’s also self-fertile and doesn’t need a pollenizer variety, he says.
Many other muscadine varieties are exclusively female. For those to bear fruit, they must be in close proximity to a self-fertile variety to pollinate.
If all goes well, Gray says it will take about seven years from the project’s start until a seedless disease-resistant muscadine appears on grocery store shelves.
The benefits of the gene-transfer technology go far beyond just muscadines and could benefit the entire grape industry, Gray says.
The disease resistant portion itself could really, really help the bunch grape growers here in Florida, since they have disease issues,” Burgess says. “If he could put the disease-resistance into those [varieties] like he did the Thompson seedless, we could have a lot larger varieties of grapes that we could grow and grow well.”
Gray also points to a vineyard of several winegrape varieties at the Apopka research center that contain varying degrees of Pierce’s disease resistance.
An earlier gene-transfer technology was applied to the vines, but Gray says there’s no reason why precision breeding couldn’t be used to develop Pierce’s disease-resistant plants.
Muscadines have natural tolerance to Pierce’s disease, but many other grapes, such as winegrapes—known scientifically as Vitis vinifera—are susceptible.