Dr. Craig Ledbetter examines apricots for symptoms of pit burn, caused by excessive heat during fruit maturation.
At the end of this month, the U.S. Department of Agriculture will cease the breeding portion of its apricot variety development program, breeding work that’s been in place in California for more than 50 years. In the next five years, the program will continue evaluating existing field selections and introducing new varieties, selections that are the result of hybridization or crosses already made.
But after that, the program’s long-term outlook is uncertain. Since the mid-1950s, a stone fruit breeder has been stationed at the USDA’s Horticultural Crops Research Laboratory in Fresno, California.
The late Dr. John Weinberger, who developed and released 37 fruit varieties during his tenure, including Flame seedless table grapes, came in 1955 to help California growers who were relocating apricot production from the mild, but populated, coastal valleys to the hotter San Joaquin Valley. Few apricot varieties did well in the new growing region, where pit burn was a particular problem.
Dr. Craig Ledbetter, geneticist at USDA’s new laboratory in Parlier, California, has been part of the stone fruit breeding program since 1987. The Parlier station, with land for field trials and close proximity to the University of California’s Kearney Agricultural Center, replaced the urban-encroached Fresno research facilities.
“Although the apricot breeding program has had a successful past, its future is questionable,” Ledbetter said during meetings of tree fruit growers held in Visalia, California. “Though some of the apricot varieties bred and released by USDA, like Castleton (released in 1963), have faded into obscurity, Castlebrite (1977) is still found today in orchards,” he said. Since Castlebrite’s debut, USDA has released nine varieties suited for San Joaquin Valley production.
Among the more recent apricot releases are Robada, and the early season varieties Apache and Kettleman. USDA-bred apricots for the San Joaquin Valley are noted for their firm and dark orange flesh. Ledbetter said the breeding program has helped increase the marketing window beyond a four- to five-week season to a two-month period.
Apricot volume and acreage has been in decline since the 1970s, when annual production ranged from 180,000 to 200,000 tons, according to the California Apricot Producers. In 2006, around 90,000 tons were produced in the state; 13,000 acres now remain.
Although many growers have shifted from processed to fresh-market varieties because of the disappearing demand for processed apricots, about 70 percent of the total volume produced still goes to processors for canning, drying, freezing, and such. Ledbetter and his colleagues have been evaluating traits important to both processing and fresh-market cultivars as part of the apricot breeding program.
Asian crosses
In the last decade, the breeding program has aimed to find early and late-season varieties as well as replace inferior cultivars with better apricots—varieties with improved size, flavor, Brix, color, and storability. Ledbetter’s also been looking for varieties that are cold hardy.
The USDA geneticist has used apricot germplasm from central Asia to enhance sugar content and introduce genetic diversity into the San Joaquin Valley-adapted apricots. The Asian varieties have added novel characteristics like white flesh, glaborous (fuzzless) skin, variable skin and flesh color, and late and longer bloom times.
In Ledbetter’s hybridization work with central Asian varieties, the small-fruited but sweet Habiju, when crossed with Lorna, resulted in a first-generation cross that was 80 grams in size. “Most first-generation hybrids are around 40 grams or less,” Ledbetter said. Crosses from the self-compatible Hunza cultivar ripen about 10 days later than Patterson, the most widely planted variety in the state.
The Hunza crosses have good sugar-to-acid ratios, good fruit firmness, and show potential as an improved processing variety, he added. Murgab, another central Asian cultivar, has resulted in apricots with white flesh, very firm fruit, and high sugars. Some of these crosses can be picked at five pounds of pressure and still be sweet, which could help reduce bruising in the market, he said.
Ledbetter is also searching for varieties well suited for drying that are large in size, are freestone and, most importantly, retain color for months in storage after drying. Some selections from crosses made with the Hunza variety are showing good color retention seven months after storage, he said.
Hybrid crosses between Badam Gakas and California cultivars have resulted in late and delayed blooming traits that could help growers avoid spring frosts. Some crosses have bloomed as late as March 28, three weeks later than traditional apricot bloom dates in California, he commented.
Cold hardiness
In recent years, USDA has collaborated with researchers in Minnesota to test selections for cold hardiness. Ledbetter said that efforts of sending seedlings to grow in Minnesota’s harsh winters were not successful, as the seedlings froze during their first winter in the orchard.
“Now, we send bud wood to Minnesota to be placed on already established rootstock,” he said. “They’ve had -39°F there, temperatures that killed the flower buds, but the grafted trees are still alive.” Ledbetter has developed numeric standards to compare apricot selections in a more statistical and valid manner.
Color is evaluated by measuring the hue angle of the fruit. For example, the early variety Apache has a lower hue angle of 81.4 compared to Poppy’s 84.2. “There’s a huge difference in color between the hue angles of 85° and 65°,” he said. Hue angle can also be used to monitor the degree of color change that occurs as fruit ripens. For the next five years, the USDA will continue evaluating and introducing new selections, Ledbetter said. “But what happens after that is a big question.”
Questionable future
Many of the hybrid crosses are in the field on trees that have yet to come into bearing, he noted. “At the end of the next five years, we may have fruit that we’ve only looked at once on the trees.” While he has plenty of selections still to evaluate, eventually he’ll run out of selections.
With USDA no longer actively making new apricot crossings, Rutgers University in New Jersey will be the lone public entity in the nation supporting an apricot breeding program. Dr. Joseph Goffreda’s work at Rutgers concentrates on the genetic improvement of apple, peach, and apricot.
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