Pear breeding moves toward better varieties
Despite problems, Bartlett remains the pear people love.
Richard Bell works to develop better pears with the flavor of Bartlett and resistance to fireblight and pear psylla, and more precocious.
One of the problems with pears is their lack of precocity. They stay juvenile, taking up valuable space and waiting just too long to grow up and produce fruit.
That problem is actually a double whammy. If you’re trying to breed better pears, perhaps looking for those that are more precocious, it takes a long time. The breeding cycle in pears from seedling cross to final evaluation has traditionally been 30 years or more.
The Bartlett pear, now 250 years old, has yet to be replaced by new varieties. Despite its problems—such as high susceptibility to fireblight—people in both North America and Europe would rather eat a Bartlett than any other pear. In Europe, its name is Williams, after the English nurseryman who first propagated the seedling discovered in about 1765.
Still, plant breeders keep trying to exceed Bartlett. The nation’s only public pear-breeding program at the USDA Agricultural Research Service’s Appalachian Fruit Research Station in Kearneysville, West Virginia, is in the process of releasing a new variety—so far unnamed—identified as US71655-014. Dr. Richard Bell, a pear breeder there, says that five more selections will graduate to advanced selection status in 2012, and they will go out to cooperators for evaluation. They’re now at the National Clean Plant Network program at the Washington State University research station in Prosser, Washington, after having been tested and found free of viruses and pear decline before propagation.
While it’s not easy to knock Bartlett out of its position, Bell said, one thing is clear: Varieties from the USDA program all rate 7 or better on the fireblight resistance scale, where 10 is perfect and 3 is Bartlett.
“Fireblight can be devastating in some years,” Bell said. “With the USDA varieties, you may get a few strikes but not the large loss of bearing surface and tree death.”
The new pear, he said, “really looks good in Oregon, Washington, and Michigan. It ripens a week after Bartlett and stores five months in cold storage without scald. The fruit is, however, a little bit smaller than Bartlett.”
The USDA became involved in pear breeding in the early 1900s, Bell said. In the 1960s, when the program was still at Beltsville, Maryland, it released three varieties, of which the best known is Magness, a high-quality but light-cropping pear with low fireblight susceptibility.
Bell has been at Kearneysville since 1980, two years after the station there was established. Since then, his program has released four varieties—Potomac, Blake’s Pride, Sunrise, and Shenandoah.
It takes a long time to evaluate a pear, Bell said. He plants 2,000 to 3,000 seedlings in most years—always trying to find potential varieties that are fireblight resistant, pear psylla resistant, precocious, and productive, with good storage life and excellent fruit quality.
The seedlings will spend eight to ten years in the early evaluation process—much of the time just spent growing and being observed for precocious bearing and fireblight resistance. The fruit is tested for quality, and survivors are increased from one tree to four for further evaluation. Survivors there go out for advanced trials—for ten more years. Cooperators—mostly university experiment stations in Michigan, New York, South Carolina, California, Oregon, and Washington—get four or five trees each to watch and evaluate while ten trees of each advanced selection are evaluated at Kearneysville. Cooperators sometimes put in larger plantings of the best prospective releases.
The trees going out in 2012 were planted as seedlings between 1984 and 1996.
“We’re trying to speed up the process,” Bell said. “We’d like to push them out to cooperators earlier and not wait ten years for the second test.”
Bell has worked on several ideas for making pears grow up faster. In apples, that’s usually done with dwarfing rootstocks, but for pears nothing comes close to the size control and precocity apple growers can get from rootstocks like M.9.
“That’s a number-one priority for pear growers in the Pacific Northwest,” he said. “Growers want smaller trees.”
Given the lack of suitable rootstocks, Bell and his colleagues decided the answer was to develop a pear variety that would be dwarfed naturally, without a rootstock. In 1999, he and Dr. Ralph Scorza developed a dwarf Bosc pear using genetic engineering to insert a gene, rolC, from the soil bacteria Agrobacterium rhizogenes. But the tree proved to be just too dwarfed—very small and slow growing.
“We abandoned that approach,” Bell said. “But we know there are several genes that will dwarf trees. There are some, like the genes used in dwarf wheat and rice, that shorten the internodes by controlling gibberellin metabolism. One of these genes is being transferred into scion varieties. It will also be tested in a rootstock variety to determine whether the transgenic rootstock imparts dwarfness and precocity to the scion.”
Bell is also interested in testing other genes involved in phytohormone metabolism that the literature suggests may be involved in growth control and tree architecture.
Today, the station has a small planting of prospective dwarfing rootstocks, including about 40 from a breeder at Cornell and about 200 crosses Bell has made. These trees rely on the genetics of Old Home x Farmingdale, the dwarfing rootstocks developed from crosses made in Illinois and at Oregon State University, and two selections from the USDA breeding program. The 200 new crosses have been budded to the Potomac scion variety and are being tested. He hopes to have 10 to 12 selections next year to propagate for further trial, with a goal of getting trees of 50 to 60 percent of full size.
While most of the nation’s pears are grown in the West, Bell sees a revitalization coming in the East as well. The East has processors that want pears for canning and for baby food, and these markets are much more willing to accept high quality fruit that doesn’t necessarily look like a Bartlett as long as it has Bartlett flavor and high processing quality.