fruit breeder John Clark

Aug 5, 2022
Arkansas fruit breeder’s progeny grown throughout the world

As University of Arkansas (UA) fruit breeder John Clark prepares to leave the program he’s helmed since 1997, his accomplishments are seen in the varieties growing throughout the world.

Over nearly 60 years, the UA System Division of Agriculture’s breeding program has released more than 60 varieties of blackberries, blueberries, grapes, peaches and nectarines. Clark is the resident director of the university’s Fruit Research Station at Clarksville, which is renowned for blackberry and grape cultivars. Arkansas genetics birthed new industries and are grown on nearly every continent.

At 65, Clark, a guitar picking distinguished professor, has spent his career designing better blackberries. In December, Clark, who has been with the university’s horticulture department since earning his Ph.D. in the early 1980s, plans to retire from leading the world’s largest blackberry breeding program.

The program’s scientists developed the parent of the Cotton Candy table grape variety. With Arkansas-bred flavors combined with California grapes, the variety is grown throughout the world. Other varieties, including Candy Hearts, Candy Dreams and Bebop, possess Arkansas parents for flavor, Clark said. Because there isn’t a large blackberry growing industry in Arkansas, variety royalties and breeding agreements help fund the program.

Blackberry gold

In 2002, Jerry and Keith Mixon, who used to own SunnyRidge Farm, a Winter Haven, Florida, grower and shipper of blueberries and strawberries, invited Clark to visit their operation and help them grow blackberries.

The Mixons planted 200 acres of UA’s new Ouachita variety in southern Georgia. While the variety was bred in a region that receives more than 1,000 chill hours during the winter, growers found the broadly adapted variety can produce well in Georgia and Florida with 450 hours.

As more companies planted the fruit, Ouachita became the backbone of the southern blackberry industry. Other regions grew the fruit, including east Texas, but the Georgia plantings were the first major effort which created the southern blackberry shipping market.

Breeding program goals include peaches without fuzz, blackberries without thorns and seedless winegrapes and muscadines. Dwarf blackberry plants are also in development.

While UA’s peaches are considered among the program’s best offerings, because of various factors and a difficult deal, growers haven’t expressed much interest in growing them, Clark said. The UA program breeds for texture differentiation.

“We have some really firm material here that nobody grows,” he said, “but, it has a place. It’s a matter of the peach industry being tough.”

Muscadine grapes on breeding vines at the UA Clarksville, Arkansas, Fruit Research Station. Crossing muscadine grapes is a major initiative of UA’s fruit breeding program. Photo: University of Arkansas

Grape developments

Because of costs and the inability of growers to compete with California due to weather challenges, UA stopped breeding table grapes and winegrapes. The program was successful in creating local market table grapes. Winegrape breeding was a small effort.

A major initiative is crossing muscadine grapes. Margaret Worthington, who will succeed Clark as assistant professor of fruit breeding and genetics in leading breeding, is expected to release a series of seedless muscadines that could eventually change the industry, Clark said.

In 2013, UA released Prime-Ark Freedom as a local market and home garden blackberry variety. When found to possess unexpected low chilling hour requirements, it proved to be a valuable fruit in the Deep South for floricane cropping and grows well in central Florida, Clark said.

Prime-Ark 45 was introduced as the first shipping quality primocane fruiting blackberry, capable of producing two crops a year (under the right conditions) and extending blackberry harvesting into the fall.

“The primocane fruiting trait that we have been working on for a number of years will change how blackberries are grown throughout the world,” Clark said.

Other prominent varieties include Shawnee, Navaho and Ponca blackberries, Ozarkblue blueberries, the Cardinal strawberry, Reliance and Jupiter table grapes, and Dazzle, Enchantment and Indulgence winegrapes.

Clark attributes UA’s success to remaining interactive and committed to the goals of developing new varieties.

“You have to have someone who is an inspired individual who is disciplined and wants to go out and work with growers to lead breeding,” he said.

Guitar pickin’ breeder

In his last year of breeding, Clark is addressing growers throughout the U.S. In those meetings, he often plays guitar instrumentals inspired by blackberries and winegrapes. He wrote “Blackberry Freedom,” “Blackberry Traveler” and “Blackberry Horizon” while walking his dog. He performs the songs on YouTube, with the UA blackberry patches as a backdrop (

In May, Clark advised Florida growers considering blackberries at that state’s first blackberry field day. He also addressed a University of Georgia breeding conference as well as meetings in New Orleans, Michigan and Chicago.

Clark recently spent a month evaluating seedlings during Arkansas’ short blackberry season, which runs June into early July. It involved long days of tasting berries, walking with feet and pants wet from the morning dew, battling bugs and visiting cooperators in six miles of plantings.

Clark inherited Arkansas’ fruit breeding program from James Moore, who died in 2017. In 1964, Moore returned to Arkansas and started the program after working in fruit breeding for the U.S. Department of Agriculture in Beltsville, Maryland. The transition to Worthington, who came to UA in 2016, is expected in December.

Margaret Worthington inspecting muscadine grapes
Margaret Worthington selects muscadine grapes for advancing toward release as varieties. Worthington is set to succeed John Clark in heading UA’s fruit breeding. Photo: University of Arkansas

“She is really talented, very enthusiastic and is an accomplished scientist,” Clark said. “The most important thing about our program is there are no shortcomings. It has been a tremendous model, the best I’ve ever seen in a university environment when someone takes the place of someone, as universities usually have gaps and all sorts of things happen that can create discontinuity.

“Dr. Worthington leads a major part of the fruit breeding effort here, and she will have all the duties when I complete my last year,” Clark said. “She is the future, in other words, of fruit breeding here.”

Clark views the future optimistically. “There’s something special about Arkansas,” he said.

Scientific recognition

At the July 30-Aug. 3 American Society for Horticultural Science annual conference in Chicago, the American Pomological Society (APS) awarded Clark the 2022 Chad Finn Ambassador Award. Through the award, APS recognizes individuals who have made significant contributions to pomology, the study of fruit and its cultivation, particularly in outreach and service.

Clark is the award’s second recipient. It is named for Finn, a research geneticist and small fruit breeder who worked at the U.S. Department of Agriculture Horticultural Research Crop Unit in Corvallis, Oregon, from 1993 until his 2019 death.

Nominating Clark was like recommending Michael Jordan for the NBA Hall of Fame, said David Karp, assistant specialist in the University of California-Riverside’s department of botany and plant sciences.

“Many, perhaps most fruit breeders, work their whole lives without producing any varieties that truly make a difference,” he said in his nomination letter.

“Cultivars that really change the game for a fruit or nut are few and far between. Dr. Clark has been so alert, skilled, and fortunate that he has truly revolutionized two major crops: grapes and blackberries.”

Although primarily a fruit breeder and researcher, Clark is a popular speaker and presenter on fruit breeding because of requests for information on the varieties he and his colleagues developed.

“This is a fabulous honor because it honors my close personal friend Chad Finn,” Clark said in a news release. “We spent over 30 years working and having fun together in fruit breeding. It’s a joy to be associated with his name.”

– Doug Ohlemeier, assistant editor

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