Grape breeding programs around the country will get a boost from a $6.5 million federal grant to continue genetic research and development of maker-assisted breeding tools for key traits in a Cornell University-led project known as VitisGen.
The first phase of the project resulted in discovery of DNA markers for 75 different parts of the genome associated with fruit quality, low temperature tolerance, and resistance to pests and diseases, said Bruce Reisch, Cornell’s grape breeder.
He leads the VitisGen project, which includes 25 scientists from 11 institutions working to improve cultivars for wine and table grape growers.
“In the end, we’d love to have a whole suite of new varieties to reduce pesticide applications and increase quality and cold tolerance,” Reisch said.
That’s the long-term goal, but in the short term researchers are mapping grape genomes, developing faster DNA tests and looking at ways to use those tests to help growers improve management, such as by identifying which strains of powdery mildew they have to inform better fungicide selections.
In terms of breeding, new DNA markers make the process better, not significantly faster, Reisch said. Most of the 15 to 30 years it takes to develop a new cultivar is spent testing.
“I don’t think there is a grower out there that wants to plant something that hasn’t been field tested,” he said. “What VitisGen allows us to do is to become much more efficient and identify potentially elite selections before we even see the fruit and be much more efficient in the use of our fields.”
The first phase of the project was funded by the U.S. Department of Agriculture’s Specialty Crop Research Initiative for $4.5 million in 2011. The second phase also is funded through a USDA-SCRI grant.
During the first five years, the team discovered a gene that controls malic acid production — surprisingly quite similar to the malic acid gene in apple trees.
The ability to control acidity will enable breeders to use specific high-acid wild grape species, which may have a desired disease resistance, and protect fruit quality by tossing out offspring carrying the known markers for sour grapes, Reisch said.
Winemakers have long controlled for acidity in many hybrid varieties by making sweeter wines, but breeding lower acid cultivars would make it easier to make drier wines from cold-hardy grapes.
Researchers also wanted to understand why hybrid grapes typically make red wines with lower tannin levels and less color than traditional Vitis vinifera reds, so they can eventually breed some of those desired wine characteristics into hardier grapes.
They found out that tannins — the class of compounds that gives wine its bitter and astringent character — in wild grapes and their descendants are often bound to a protein that changes how they are extracted during wine making.
They also found that hybrid grapes have a different composition of anthrocyanins — the color compounds — than vinifera grapes. The next phase of the project will look for the genetic roots of these traits.
Other important new markers include those for root knot nematode resistance in rootstocks and multiple markers for powdery mildew resistance, Reisch said.
Economists working with the project estimate that adoption of a powdery mildew resistant cultivars could save raisin grape growers in California’s San Joaquin Valley $186 per acre, or about $36 million a year.
Of course, adoption of new varieties takes time and, especially in the wine industry where European vinifera varieties are prized; even beneficial new cultivars face an uphill road to widespread adoption. But Reisch said the growing appreciation for hybrids such as Vignoles shows there is demand for new grapes.
“There is certainly a place for new varieties in the established growing regions, and in the eastern U.S. there are growers who are willing to experiment and use the full diversity of the grape genus. It’s a great thing to see,” he said. “There is so much we are just discovering about the grape genome, and we are still finding plenty of major genes for use in grape breeding.”
And the more they discover in the grape genome, the more complex it turns out to be.
Many key traits are controlled by more than one gene: some major, offering a significant amount of cold tolerance for example, while minor genes offer just a small boost. But finding all of them allows breeders to stack them and bring more cold tolerance or resistance to new selections.
“We’re trying to understand which genes complement each other and give us more stable and long-lasting resistance,” Reisch said. In traditional breeding, he can test seedlings for powdery mildew resistance, but he can’t see how many resistance genes an individual grape is carrying. “Genetic testing allows me to stack genes. That makes us, as breeders, so much better than we were before.” •
– by Kate Prengaman