A Field Trip to Wolfskill

Photo credit: Jessica Youngblood

May began with NGRA’s Mid-Year Board Meeting in Winters, CA. The location was chosen so that Board members could visit the Wolfskill Germplasm Repository there—many for the first time.

UC Davis owns the land where the repository lives: the Wolfskill Experimental Orchards. Named for the family that owned and deeded it to the university, the site has just over 150 acres planted with conservation blocks for 14 fruit and tree nut commodities, spanning everything from almonds to avocados. The USDA’s Agricultural Research Service leases land within the orchards for the repository. Officially called the National Clonal Germplasm Repository and sometimes referred to as the Davis Genebank, the Wolfskill Repository is part of the USDA-ARS National Plant Germplasm System.

USDA-ARS’s Claire Heinitz is the curator there. As our group meandered among the vineyard rows, she and longtime ARS viticulturist Bernie Prins explained that the Wolfskill Repository is home to two plants each of more than 4,000 accessions (defined as genetically distinct examples) of 36 species of grape, including Vitis vinifera and wild grape varieties and native rootstocks from around the world. Together with its sister repository in Geneva, NY, which maintains 1,416 accessions from 27 species of cultivated hybrids with an emphasis on cold-hardy grapevines, these USDA-ARS sites comprise the largest grape germplasm collection in the US and the most diverse on the planet. But not a single grape is used for production or fresh-market sale. That’s because the value in these vines isn’t in the fruit they produce—it’s in their DNA.

These plants are critical assets for grape breeders worldwide. To underscore that point, NGRA’s Board tour of the repository took place during what grape breeders call “crossing season,” when grapevines are flowering and their pollen can be collected. Evidence of crosses in process was everywhere throughout the vineyard, in brown paper bags attached to flowering vines. Each bag serves to isolate the nascent flowers, allowing breeders to introduce the pollen of another vine with traits of interest and exclude all others. The hope is that the germinated flowers yield the seeds of a new hybrid variety.

We also happened to cross paths with two visiting grape breeders, one from South Korea and one from New York, there for what they called “allele mining.” Armed with oversized tweezers, they were searching for and making crosses with (using said tweezers) vines with specific traits needed to advance their grape breeding goals. This painstaking work relies on research underway now to genotype the entire Wolfskill collection and identify accessions with desirable alleles (genetic traits), creating a kind of catalog for grape breeders. That way, scientists seeking to introgress traits like drought or heat tolerance, disease resistance, upright growth habit, etc., into other, perhaps commercially important varieties will know where to find them. It’s not splashy, sexy research, but it’s vital to accelerating the grapevine improvement and variety development efforts that will sustain the grape and wine industry through climate change, invasive pest incursions, labor shortages and more.

According to curators at the Geneva Genebank, one of the greatest germplasm success stories of all time took place in 19th- and 20th-century Europe. Grapevine pests and pathogens unwittingly imported from North America were wreaking havoc on European vines and severely impacting their fruit quality and yield. North American Vitis species provided resistance to these diseases, sparking an interest in hybrid varieties and ushering in a more global view of grape breeding—one where obscure or native varieties prove useful in averting disaster.

Today, with advances in traditional breeding and biotechnology, our grape germplasm repositories are goldmines of genetic assets with riches yet to be fully explored. The solutions to our modern viticultural concerns may well be preserved among the research blocks there—living archives of grapevines’ genetic diversity.

The USDA-ARS grape germplasm repositories aren’t widely known to industry representatives, so I was pleased that NGRA’s Board members were game to visit these humble research sites. We learned a lot and saw vines that might one day hold the key to the grape and wine industry’s sustainability…and survival. That’s definitely worth the trip!

Donnell Brown