Ksenija Gasic heads Clemson University’s peach-breeding program, which was recently revived after a 25-year hiatus.

Ksenija Gasic heads Clemson University’s peach-breeding program, which was recently revived after a 25-year hiatus.

Richard Lehnert

One of the great things about being a peach breeder in a new peach breeding program is no hangover—nothing left, no seedlings to evaluate, no big shoes to fill.

That’s the situation Dr. Ksenija Gasic finds herself in. She came to Clemson University in Clemson, South Carolina, in 2008 to restart a peach breeding program that had been ­dormant for 25 years.

That upside is also a downside. Since it takes about three years from seeds to fruit, just this year she began evaluating seedlings from crosses she made in her first year at Clemson.

“I’m just getting ready for orchard work,” she said in early May. When Good Fruit Grower visited and saw her new plantings on May 19, the earliest peaches were just ripening. “Peaches bloomed about two weeks earlier than usual this year,” she said. She had about 1,200 new seedlings to look at this spring.

RosBREED

There are other upsides to being brand new in South Carolina. As the peach breeder in the second largest peach-producing state (behind California), there’s plenty of grower enthusiasm for what she’s doing, not just in South Carolina but across the Southeast in general. There are four other peach breeding programs serving the Southeast—William (Dick) Okie’s USDA program at the Southeast Fruit and Tree Nut Research Laboratory in Byron, Georgia; Ralph Scorza’s USDA program at the Appalachian Fruit Research Station in Kearneysville, West Virginia; John Clark’s program at the University of Arkansas; and Jose Chaparro’s program at University of Florida in Gainesville.

“It’s a great time to be a peach breeder,” Gasic said. She’s part of the RosBREED project (www.rosbreed.org), which is bringing U.S. Rosaceae breeders together. Rosaceae include several species, including apples, sweet and tart cherries, peaches, and strawberries. It is thought that all these species share genes; the gene that makes an apple red makes a cherry red or a peach red, too.

“As the peach breeder in a new program, I’m in excellent position to use RosBREED information right from the start,” she said.

A major goal of the four-year project, which was funded two years ago at $14.4 million (with half coming from state resources and the other half from the federal Specialty Crop Research Initiative), is devoted to the search to identify locations of genes that govern specific fruit quality traits, to find markers for them, and then to find tests that will locate those markers easily.

“RosBREED focuses on bridging the gap between genomics knowledge and breeding application,” Gasic said. “I’m a peach breeder. I create the trees. What I need is a more efficient way to evaluate new seedlings and remove unwanted hybrids while they are still in the greenhouse and never actually plant them in the field or have to wait for the fruit.”

DNA

The specific tools she would like are lab methods that could evaluate the DNA in a young plant and look for a particular string of nucleotides associated with a trait of interest. “We need a user-friendly test that can tell us, yes or no, does this seedling have this trait,” she said.

For some traits, like disease resistance, it may be governed by one gene and thus the answer could be, yes or no. It is qualitative. Other traits, like fruit flavor, are quantitative. “Many genes contribute to the trait,” she said. “Maybe only 60 percent of a trait is explained by one or a few markers. That’s still very useful information.”

For some of the fruit quality traits she’s looking for—fruit firmness, texture, and flavor—markers have already been found. “The entire peach genome has been sequenced,” Gasic said, “but it’s just a string of nucleotides until it’s found what pieces of the genome govern what traits.”

The genome sequence was published April 1 last year by a team led by molecular geneticist Dr. Bryon Sosinski at North Carolina State University in Raleigh, North Carolina. The DNA sequencing was done on a Lovell tree located not far from Gasic’s new plantings at Clemson’s Musser Fruit Research Farm.

Clemson received about $400,000 of the RosBREED money to support Gasic’s work and also that of Dr. Greg Reighard, who is an authority on fruit tree genetics and peach rootstocks.

Ramping up

This year, Gasic is ramping up her program. The first year, she created 1,200 hybrid seedlings, the next year 1,700. This year, she planted 8,000. Without markers to improve breeding efficiency, she will have these 11,000 trees to evaluate for at least two fruiting seasons in the field. With markers, superior seedlings with trait combinations she is looking for could be selected prior to field planting, therefore reducing the number of trees planted in the field and improving breeding efficiency. Other key traits that are important to her are fruit size, flavor, nutritional content, blush—red color of the skin—and disease resistance.

In the RosBREED project, the four participating peach demonstration breeders—Tom Gradziel, at University of California, Davis; David Byrne at Texas A&M; John Clark in Arkansas; and Gasic at Clemson—have common goals such as maintaining and improving fruit quality (including flavor, firmness, and appearance), productivity, size, and season extension. These target traits are complemented with specific needs of local areas—ease of processing, disease and pest resistance, a greater diversity of fruit types, and adaptation to chill zones.

Gasic’s goal is to produce about 3,000 seedlings a year. She does much of the crossing work herself, emasculating flowers and applying pollen by hand. Pollen, because it doesn’t transmit diseases like plum pox, can be obtained from other places in the world, so she taps into gene pools in Serbia, Brazil, Italy, and other places where peaches are grown. She has a doctoral and a master’s student working with her, as well as undergraduate students and a research technician.

Peach pits, cleaned and stratified, are planted in the greenhouse and hybrid plants are grown over the winter. In March and April, they’re moved outside into fields. The next year, some flowers will appear and result in fruit.

“Once the tree bears fruit, it usually takes two years to decide whether a seedling should be kept and moved to the next stage. About five percent make that cut,” she said.

Gasic would love to improve efficiency of this traditional way of doing things and is looking forward to discovery of more markers and more tests that can be done much earlier in the breeding process.