Dr. Kate Evans
The Pacific Northwest fresh pear industry will allocate more than $200,000 over the next three years to launch a pear rootstock breeding program in Washington.
A dwarfing pear rootstock would enable pear growers to shift to more efficient production systems and use labor-saving equipment, as has happened in apples thanks to rootstocks like Malling 9.
“It’s exciting that the pear industry has recognized that this will help them move forward into that next stage of production,” said Dr. Kate Evans, Washington State University’s pome fruit breeder in Wenatchee. “Think about the huge advantages you have in apple production because of dwarfing rootstocks and high-density plantings, and all the mechanization you can bring in.”
Small trees and fruiting walls also produce fruit of more consistent maturity than the big, old trees that are still common in the pear industry, research shows.
It’s almost a century since Malling 9 was discovered as a chance seedling in France. Though many more dwarfing apple rootstocks have been introduced since then, there has been much less effort directed towards developing Pyrus rootstocks for pears.
That’s partly because pear growers in other parts of the world have been able to shift to high-density systems using quince (Cydonia) rootstocks.
Before joining WSU in 2008, Evans worked for East Malling Research in England, where she released the Quince H rootstock.
Quince H is being used with success in Europe, particularly in Italy. Even in Poland, which has cold winters, growers use dwarfing quince rootstocks with the idea that they will just replace the orchard if the trees succumb to cold, perhaps once every 20 years or so. They still find the plantings to be profitable.
But quince is not thought to be cold hardy enough for the Pacific Northwest. Also, some rootstock-variety combinations are better than others, and there are reports that d’Anjou, Washington’s top pear variety, is not productive on quince.
Crosses
With the new funding, Evans plans to start a rootstock breeding program in Wenatchee. WSU already has some crosses between Bartlett, d’Anjou, and Comice that were made by a graduate student for a previous project. WSU genomicist Dr. Amit Dhingra has been maintaining that material in Pullman.
Recent research at Oregon State University in Corvallis revealed that the Old Home x Farmingdale 87 rootstock, which is widely used in the Northwest, was misnamed and is actually a cross of Old Home and Bartlett. (See “Old Home x Bartlett?” in the December 2013, Good Fruit Grower.)
“That made us think that perhaps there was some value in looking at some of those Bartlett seedlings we had,” Evans said. “We had this material, so why not?”
Initial screening shows a wide variation in vigor. Some of the most promising candidates will be planted in Wenatchee for a small-scale trial to find out how well they control the vigor and size of commercial pear varieties used as the scions. Dhingra is also looking at how well they would propagate. A common problem with Pyrus rootstocks is they don’t root very well.
Evans also plans to make new crosses. She has a range of germplasm at WSU’s Sunrise Orchard in a pear rootstock parent collection she established five years ago. Having good material to cross is the key to starting a breeding program, she said.
Most of this material came from the pear collection at the National Clonal Germplasm Respository at Corvallis, Oregon. Evans spent some time walking around the collection looking for interesting species. One that she picked out was Farmingdale, which, though not dwarfing and not a parent of OHxF 87, does have high resistance to fire blight.
“One of the nice things about Pyrus is it’s quite diverse, and for the most part willing to cross pretty well,” she said. “There’s an awful lot of opportunity to bring in some germplasm that would suit this industry.”
A benefit of using what she calls “slightly exotic germplasm” is that it can introduce other important characteristics, such as resistance to fire blight and tolerance of pear decline, as well as dwarfing.
Longer process
Breeding new rootstocks tends to be a longer and more difficult process than breeding varieties, Evans said. That’s because rootstocks can’t be crossed until they grow into trees and bloom. Also, it’s more difficult to evaluate the growth characteristics of a rootstock than to spot an exciting new apple growing on a tree. The differences are more subtle.
“My personal view is the amount of testing you should do of a new rootstock is more than for a new scion because if you make a mistake and release a new rootstock out to the industry, it can have a much more devastating long-term consequence than a new scion,” she said.
Advanced selections need to be tested with different scions and in different growing conditions, and she likes to collect at least six or seven years of data from trials. “What inevitably happens is you have to go through a few rounds of that to cut the numbers down,” she said.
That’s why on-going support by the pear industry was important.
“I wanted to start this with a reasonable level of commitment from the industry that they would be prepared to look at this in a long-term way,” Evans said. “It’s a waste of everyone’s time, effort, and money to go through the very early part and not follow through.”
Figuring out how best to multiply any promising selections for replicated trials will be part of the project. Dhingra, who is collaborating with Evans, brings expertise in tissue culture and micropropagation.
Genetics
Genetic markers enable scientists to identify traits in plant DNA from young seedlings without needing to grow a whole tree, but markers will not be developed for the project initially. Evans said some markers have been identified for the dwarfing trait in apples and she and her colleagues plan to see if those might work in pears, since the fruits are related.
Dr. David Neale, geneticist at the University of California, Davis, is working on a project jointly funded by the Northwest and California pear industries to assess the genetic variation of pears in the national repository in Corvallis, Oregon. The genetic data will be overlayed with the visible, or phenotypical, variations observed between the pear species.
“Long term, we’re trying to do more and more phenotyping of the collection so we can potentially develop more DNA-based tools to help us with breeding selection,” Evans said.
Neale, Dhingra, and Evans are part of a Pear Genomics Research Network created about two years ago to coordinate the various research efforts relating to development of pear rootstocks. Other scientists involved include Dr. Richard Bell and Joseph Postman with the USDA ; Rachel Elkins and Dr. Pedro Martinez-Garcia at UC; Dr. Stefano Musacchi at WSU; and Dr. Todd Einhorn with OSU.
Einhorn is heading a project to evaluate elite pear rootstock material, including quince and Amelanchier selections (read “Promising pear rootstocks,” from the April 15, 2015 issue.
Both quince and Amelanchier are pome fruits. Some of the best selections will be planted in replicated trials in Washington and Oregon. •
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