PARLIER, Calif. — For David Ramming, a research horticulturist with the U.S. Department of Agriculture’s Agricultural Research Service in Parlier, finding that winning table grape variety is really a numbers game.

The more hybrid crosses Ramming makes, the greater his chances are of developing a variety that has the good eating quality, attractive appearance, seedlessness, large berry size, low berry shatter, yield and a host of other desirable attributes that he’s seeking.

Each year Ramming tries to make about 200,000 crosses, and most involve table grapes although he also is working to develop raisin-type varieties.

Within the first year, he will have weeded out all but about 100 selections, or 0.5%.

“Making the crosses is the easy part,” Ramming said. “But now evaluating that 100 to see whether they’re commercial, should we still use them for breeding or should we get rid of them after we’ve already gotten rid of 99.5%. So breeding is a numbers game.”

If a selection makes it through the early cuts and looks promising, Ramming meets with the California Table Grape Commission’s research committee to seek members’ input.

During the summer, the USDA invites research committee members as well as growers to sample some of the up-and-comers.

“We solicit and evaluate comments on our selections,” he said.

Ramming also works with Mary Lu Arpaia, an Extension horticulture specialist at the nearby University of California Kearney Agricultural Research and Extension Center, Parlier.

Arpaia conducts produce sensory testing of new varieties, including table grapes.

It typically takes about 15 years to develop a new variety, Ramming said, although crimson was released after nine years.

“The reason why it was nine years instead of 14 or 15 is because there was really no competition,” he said. “It was a late red seedless. The only other late reds are seeded, so we didn’t have to do that final large-scale production trial.”

One of the selection criteria is a candidate must be better than varieties already on the market, Ramming said.

Among more recent releases are autumn king, a large, late-season white seedless grape; summer royal, a mid-season black seedless grape; and sweet scarlet, a mid-season red seedless grape with a distinctive muscat flavor.

One selection nearing release is valley pearl, an early- to mid-season seedless green grape with a large, round firm berry bordering on a crisp texture, he said.

A patent has already been applied for, and the USDA is in final negotiations with the Fresno-based California Table Grape Commission over licensing.

Much of Ramming’s efforts recently have turned to incorporating resistance to powdery mildew and Pierce’s disease into new varieties.

Typically this entails finding natural resistance in another grape species, such as one from China that is powdery mildew resistant and is housed at a USDA’s germplasm facility in Geneva, N.Y.

Then the challenge is to crossbreed those plants, which frequently have undesirable agronomic characteristics, with table grapes to develop disease-resistant yet tasty new varieties.

Ramming also is working with Andy Walker, a grape geneticist at University of California, Davis, who has found naturally occurring sources of Pierce’s disease resistance.

The table grape commission supports much of the USDA breeding program through a per-box assessment. In the past, the USDA made new varieties available worldwide for propagation and production.

But under an agreement made about 10 years ago, the table grape commission can apply to be the exclusive licensee for a new variety. This allows the commission to govern distribution of plant material.