UC Davis has received a landmark gift of more than $12.5 million, the legacy of one of Napa Valley’s oldest wine families.

Louise Rossi had been a longtime supporter of UC Davis before her death last February at the age of 99, but her gift, which will result from the sale of the 52-acre Rossi Ranch in St. Helena, is one of the largest donations ever made to UC Davis.

The bequest will increase the endowment of the Rossi Prize, which Louise Rossi and her brother Ray, an alumnus of UC Davis, established for graduates of Napa Valley high schools who want to study viticulture and enology at the university. The gift will also pay for equipment for the Robert Mondavi Institute of Wine and Food Science, scheduled to be completed in June 2008, and endow one or more faculty positions and support research in the world-renowned department of viticulture and enology.

Louise and Ray Rossi established the Rossi Prize in 1979 in honor of their parents, Fred and Rachel Rossi, who immigrated to the Napa Valley in the late 1880s from Switzerland and Italy. They met and married in the valley and purchased the St. Helena ranch in 1905. Their three children were Arthur, born in 1901, Ray (1906), and Louise (1907). Fred Rossi became a successful grape grower, and after his death in 1922, Arthur Rossi took charge of the ranch and became both a grape grower and winemaker. Clients who bought Rossi grapes included Robert and Peter Mondavi at Krug Winery. When Arthur died in 1950, Robert Mondavi was one of his pallbearers.

After Arthur Rossi’s death, the remaining Rossis, Rachel, Louise and Ray, ceased making wine and concentrated on growing grapes. Rachel Rossi died in 1958 and Ray in 1997.

Louise Rossi, who never married and died without heirs, continued to live in the simple white farmhouse on the Rossi Ranch. Those who gathered Friday at the event in the barn where her brother had made his wine shared stories of feisty, opinionated and frugal lady, deeply committed to stewardship of the land.

“If you owed Louise a dime in 1940, in 2007 she’d remember,” said Ted Hall, a neighbor and owner of Long Meadow Ranch. Hall is also an investor in Frog’s Leap Winery, which bought the Rossi property, making the bequest possible.

Before her death, Louise Rossi sold grapes to Frog’s Leap, and made friends with Frog’s Leap owner and winemaker John Williams. The traditional and organic farming practices of Frog’s Leap were in tune with Rossi’s views, and before her death she made plans to sell the ranch to the winery.

Williams, a graduate of UC Davis, said he will live in the farmhouse on the property. “What you see here will be this way for years to come,” he said. “It’s nice to know this piece of Napa is alive.

“Louise believed in values of family, farming and sustainable agriculture,” Williams said. “She knew UC Davis shares those values and will promote them.”

“Louise Rossi and her family so typified the spirit of California agriculture,” said UC Davis Chancellor Larry Vanderhoef. “We at UC Davis are quite humbled to be the recipients of their quiet generosity and the beneficiaries of their many decades of hard work.”