Breeder Nnadozie Oraguzie stands in a Phase 1 block planted in 2011 and 2012. He’ll begin collecting fruiting data when the trees are three to four years old.
Breeding new varieties of fruit is all about numbers—it takes thousands of crosses to find one worthy of commercialization. Researchers at Washington State University are using genetic technology to make smart crosses to improve program efficiency but, more importantly, to increase their odds of success.
WSU has a long cherry and stone fruit breeding history dating back to the late 1940s. The blush variety Rainier was the program’s first release in 1960. Active breeding work stopped in the mid-1980s, but restarted two decades later, integrating state-of-the-art genetic technology.
Cherry growers in Oregon and Washington, through financial support from the Oregon Sweet Cherry Commission and the Washington Tree Fruit Research Commission, revived the program in the mid-2000s and armed it with new objectives and technology. Today’s breeding program at WSU uses genomic tools to select which parents to cross, making it unique among U.S. cherry breeding programs.
Dr. Nnadozie Oraguzie joined WSU’s cherry breeding program in 2008 as its stone fruit breeder-geneticist. He works closely with other WSU scientists who apply genetic tests to potential cherry parents to map genetic traits.
By looking at the DNA markers for specific traits, such as self-fertility, fruit size, fruit firmness, and disease resistance of parents used for crosses, Oraguzie can zero in on markers likely to produce a certain size or other desired traits.
“By DNA-testing the parents first, we know the genotypes that we have available and we can make informed decisions when matching parents,” said Oraguzie in an exclusive interview with Good Fruit Grower. “If you don’t have the right genotypes when you first make the crosses, you’re doomed to fail from the very beginning.”
DNA testing is also applied to the offspring so that inferior seedlings can be eliminated immediately, before even being planted in the field for evaluation, he explained.
“We are the only sweet cherry breeding program in the United States that uses DNA technology like this,” Oraguzie said. “The DNA testing is what makes our breeding program stand out.”
He estimates that from the thousands of crosses made, about two-thirds are eliminated without ever being planted in evaluation plots.
When Oraguzie was in New Zealand doing breeding work prior to WSU, he said only one out of every 5,000 crosses had a chance at becoming a new variety. “We’re trying to change those odds with DNA information,” he said. “Once we have the right genotypes, we can do smart breeding, which should improve our chance of success.”
When Oraguzie joined WSU in 2008, a few hundred seedlings were in the ground from crosses made in the first few years of the program’s restart. Today, there are about 10,000 seedlings planted in the field and the program has evolved into three phases.
Phase 1 includes making crosses, planting own-rooted seedlings in the field, and evaluating fruit. Phase 2 includes replicated trials of grafted advanced selections at three locations (WSU’s Roza research orchard in Prosser, Oregon State University’s research station in Hood River, and a grower cooperator’s orchard in Washington).
In each location, five trees of each genotype are planted next to a comparable commercial variety. In Phase 3, replicated trials of elite selections are grown at Prosser and grower-cooperator orchards in Washington and Oregon. The number of trees planted expands to 100 at each location as Oraguzie looks for fatal flaws that may have been hidden earlier.
“We have to plant enough trees in Phase 3 to achieve enough volume that can be commercially handled so we can obtain packout and storage data,” he said. “We want to look at things that affect cullage rates, such as pitting and cracking.”
Throughout the three phases, selections are continually evaluated, with a host of data collected, from date of bloom time and cold hardiness to fruit quality. For seedlings in Phase 1, three years of fruiting data are collected before a decision is made to advance a selection to Phase 2. Oraguzie typically has to wait for three years before the trees in Phase 1 begin producing fruit for evaluation.
However, there are exceptions to the three-step selection process.
Oraguzie and his grower advisory team have the ability to fast-track a selection that shows exceptional fruit qualities in its first year of fruiting.
“If we see something that looks like an exceptional performer—based on only one year of data—we can send wood to the nursery for propagation instead of waiting for three years of data before ramping up the number of trees for advanced evaluations,” he said.
It takes two years to get a tree back from the nursery for planting, so this has been an important step in speeding up the time involved in the breeding program.
And though a selection can get a fast track into Phase 2, data is still collected from the initial Phase 1 tree, as well as from the named cultivars or numbered selections that produced the cross. The fast-track option has only been used on about ten selections thus far—out of about 5,000 trees that are fruiting.
One of the biggest costs involved with the breeding program is management of the thousands of trees planted in the different phases. In looking for ways to minimize tree management costs at WSU’s Roza block, Oraguzie will soon begin budding five selections on trees planted to the UFO training system (Upright Fruiting Offshoots) developed by fellow WSU researcher Dr. Matt Whiting.
In Phase 1, with 10,000 trees planted, the majority of the program’s costs are in the trees, said Oraguzie. It’s easy to do the math of growing five selections in the space of one tree. “By putting five selections on the upright offshoots, we could reduce tree planting costs by a fifth or 20 percent.”
In addition, there are several advantages to budding the selections on a rootstock versus their own roots. Seedling trees are often erratic in their flowering, he noted. If new selections are budded to size-controlling rootstocks (as is the case with the UFO trees), flowering will be more uniform. Fruit quality can also be quite different when comparing fruit grown on rootstock and own roots.
“Fruit quality will be the same from the start and we’ll know right away what to expect from selections planted on rootstock,” Oraguzie said.
Breeding program goals
The goal of the cherry breeding program of Washington State University is straightforward: develop high quality sweet cherry cultivars that have high consumer appeal and are suitable for growing in the Pacific Northwest.
WSU’s fruit breeder Dr. Nnadozie Oraguzie is working to develop improved varieties that meet the following objectives that define targets for the new varieties and guide the breeding work.
1. Early mahogany variety (Chelan replacement)
2. Late mahogany variety (Sweetheart replacement with powdery mildew resistance)
3. Early blush variety (Early Robin replacement)
4. Late blush variety (Rainier replacement)
5. Midseason mahogany variety (Bing replacement that is larger and firmer)
6. Range of early, mid-, and late-season varieties suitable for mechanical harvest
In addition, self-fertility is an overriding goal for any new cultivar. Self-fertile varieties would reduce reliance on the use of bees for pollination and help reduce grower costs.
“We want to improve on the varieties that are currently the industry standards, focusing on early and late-season cultivars to extend the harvest window for Pacific Northwest cherry growers,” Oraguzie said.
He added that several current varieties need applications of gibberellic acid to improve firmness, have moderate fruit size, require bees for pollination, and are susceptible to cracking, pitting, and powdery mildew.
WSU’s cherry breeding program uses DNA testing to identify genetic traits like fruit size and firmness. DNA markers are just beginning to be used to identify disease traits like resistance to powdery mildew and bacterial canker, he said.
In ten years, he believes researchers will be able to identify DNA markers for other genetic traits like flavor and phytonutrient traits, giving breeders even more tools for developing improved varieties.