Since the pear industry still lacks a dwarfing rootstock, Dr. Todd Einhorn is experimenting with ways to improve light penetration in standard pear trees.
A dwarfing pear rootstock—equivalent to a Malling 9 rootstock for apples or Gisela rootstock for cherries—is needed so that pear growers can improve production efficiency and take advantage of new technology.
“I really think it’s the missing link,” said Dr. Todd Einhorn, horticulturist with Oregon State University in Hood River, who believes that dwarfing rootstocks are key to the future of the pear industry for a number of reasons.
Smaller trees would increase the efficiencies of many orchard practices, improve the efficacy of pesticide applications, and reduce labor needs. In addition, a small-canopied tree on a dwarfing rootstock tends to be more yield efficient, if managed properly.
Today’s typical pear orchard in the Mid-Columbia region has trees spaced about 14 feet apart with 18 feet between rows. A problem with a big old pear tree is that the inner third of the canopy is composed solely of structural wood, Einhorn says, and the middle third of the canopy has little fruit because it is heavily shaded. Only the outer third is productive. “You just have an inefficient use of space,” he said.
Some growers have planted medium- or high-density pear orchards, but it’s a struggle to manage the trees without a dwarfing rootstock, Einhorn said. Old Home x Farmingdale 87 and 97 rootstocks are commonly used in modern plantings, but he does not think they are dwarfing enough, particularly for the vigorous d’Anjou variety. He compares OxHF.87 to the semidwarfing M.26 or even M.7 in apples.
The Horner 4 and 10 rootstocks, which have been tested at OSU, are yield efficient, but do not result in small trees.
Growers in other parts of the world, including Europe, use quince rootstocks for high-density pear systems, but the commonly used Quince A, Quince BA-29, and Quince C have not been deemed hardy enough for the Pacific Northwest. They have been used in the Medford, Oregon, district where the climate is more moderate. There is evidence that the Polish quince rootstocks, S1, S2, and S3, are cold hardy, but Einhorn said he does not know if they are compatible with the pear varieties grown in the Pacific Northwest.
There could be other quince rootstocks that are more cold tolerant that haven’t been tested as pear rootstocks yet. The National Clonal Germplasm Repository in Corvallis, Oregon, has more than a hundred quince accessions from around the world. Joe Postman, curator at the repository, is sending cuttings of about 50 of them for Einhorn to test in Hood River, starting this month.
Some, because of their origin, are likely to be cold hardy, though how they would work as pear rootstocks is as yet unknown. Graft compatibility with commercial pear varieties would have to be tested.
Einhorn will first of all test the plants in freeze chambers for cold hardiness. He will study the mechanisms of cold injury and the physiological traits of the plants. Hardy material could be used by Dr. Kate Evans, pome fruit breeder at Washington State University, in crosses to develop new pear rootstocks. Quince (Cydonia) and pear (Pyrus) have been crossed in the past. The quince-pear rootstock Pyronia is used commercially, but is not very dwarfing, Einhorn said.
Growing the future
After testing the quince plants in the lab, Einhorn intends to bud and grow the most promising ones in the field to study their compatibility with commercial varieties. Some compatibility problems might not be evident for many years. He’ll also assess fruit quality and size, and compare performance of the quince with a range of commercial rootstocks.
In addition, Einhorn plans to test clones of serviceberry (Amelanchier) that have been developed as dwarfing pear rootstocks in Germany. They are being imported into the United States by nursery owner Dave Weil of Dundee, Oregon.
Data from Germany show that they are significantly dwarfing and compatible with pear varieties they have been tested on, such as Comice and Hardy. Einhorn hopes to receive the rootstocks for testing in 2010. •