An Oregon State University researcher is testing pear rootstocks that might have the potential to improve early bearing of pear trees, control tree vigor, and enhance production of high-quality fruit in the Pacific Northwest.
There is not currently a dwarfing, precocious rootstock available for pears as there is for apples. Old Home by Farmingdale 87, the industry standard, reduces pear scion vigor by 30 percent compared to a seedling rootstock.
The industry would like to have a rootstock that is about 50 percent the size of a seedling rootstock and is more precocious, particularly for d’Anjou, which takes a long time to come into production.
Commercially available dwarfing quince rootstocks, which are commonly used for pears in Europe, are reputed to not be hardy enough for the Pacific Northwest. A multi-year evaluation of the freeze resistance of these selections confirmed this suspicion.
Dr. Todd Einhorn, horticulturist at the Mid-Columbia Agricultural Research and Extension Center (MCAREC) in Hood River, says some quince selections, however, are hardy, but other issues associated with quince—such as graft incompatibility, iron chlorosis, pear decline, and fire blight susceptibility—have not been evaluated for these selections.
Einhorn obtained a large number of quince accessions from the National Clonal Germplasm Repository at Corvallis, Oregon, and tested them for cold hardiness. He found 22 quince selections that were as hardy or hardier than the commonly used rootstocks OHxF 87 or OHxF 97 and could withstand temperatures down to -22°F (-30°C).
In 2016, he will put the top ten of the quinces from his tests into a trial in Wenatchee and Hood River, with and without interstems and with Bartlett and d’Anjou as the scions. The trees are being produced in the nursery now.
In addition, Einhorn is evaluating Quince Eline, a purported cold-hardy quince rootstock, which is being propagated in The Netherlands and appears to be hardy down to -12°F. Compared with OHxF 87, it looks good, he said, but it is not as productive as Amelanchier
(serviceberry) which he is also testing as a pear rootstock.
Amelanchier, which is native to North America, is a very cold-hardy plant that grows well in Canada. It can withstand a -40°F temperature in mid-winter with little to no browning of the wood. Dr. Michael Neumüller, breeder at the Bavarian Center for Fruit Crops in Germany, has developed Amelanchier rootstocks, which are compatible with Beurre Hardy and Comice. Compatibility with other pear varieties is not yet known.
In a trial in Oregon with d’Anjou, trees on the Amelanchier rootstocks were half the height of those on OHxF 87 and produced 20 pears per tree (14 bins per acre) last season in the third leaf, and the fruit was large (box size 70), Einhorn reported. “To me, that’s remarkable.”
The trees on Amelanchier did not have much extension growth and were loaded with fruit buds. The leaf-to-fruit ratio was 40:1. The number of leaves per tree, interestingly, was equivalent to trees on OHxF 87, but those trees had no fruit.
Einhorn, in collaboration with Tom Auvil, research associate with the Washington Tree Fruit Research Commission, also oversees on-farm trials with the Horner rootstocks, which were developed more than 30 years ago by Oregon nurseryman David Horner from open-pollinated Old Home by Farmingdale material.
Initial trials indicated that two selections, Horner 4 and Horner 10, produced good yields and fruit size, compared with OHxF 97. Horner 4 seemed precocious, even though it produced a large tree.
In a recent orchard trial in Wapato, Washington, with Bartlett planted at 1,089 trees per acre (4-by-10 feet), OHxF 87 produced 55 bins per acre in the fifth leaf, compared with 48 bins for Horner 4 and 44 bins for Horner 10, but fruit from the Horner 10 trees was smaller than fruit on trees on the other two rootstocks.
OHxF 87 in a mirror trial with Golden Russet Bosc produced 43 bins per acre compared to 33 bins per acre for Horner 4 and Horner 10. Fruit size of Bosc was largest for Horner 4.
In an orchard trial in Oregon with d’Anjou, with 427 trees per acre, trees on Horner 4 were 50 percent larger than those on OHxF 87 or Horner 10. OHxF 87 produced 42 bins per acre (107 pears per tree) in the sixth leaf, compared with 42 bins for Horner 4 and 29 bins for Horner 10. Einhorn said the grower has not been deterred by the vigorous Horner 4. In fact for d’Anjou, Horner 4 might be a good fit for sites with low vigor or replant situations.
A ten-year rootstock trial with d’Anjou and Bosc pears that Einhorn ran in collaboration with Tim Smith, Washington State University Extension specialist, showed that of the OHxF rootstocks, OHxF 87 was the best in terms of production and fruit size. But some growers have reported that, after about 10 years, Bartletts on OHxF 87 start to become tired and weak.
Einhorn said in a 15-year-old planting at MCAREC of Bartlett on OHxF 87 and 97 rootstocks, he did not find that to be the case and OHxF 87 outyielded 97. However, with Red d’Anjou as the scion, OHxF 87 can produce a weak tree and not perform so well. With this variety on OHxF 87, closer tree spacing, some fruit thinning, and vigor promotion might be advisable, he said.
In 2013, Einhorn began a rootstock and systems trial with d’Anjou as the scion. He is comparing OHxF 87, OHxF 69, and the German rootstock Pyro-233. The trees are trained to three systems: steep upright V with trees leaning in alternate directions; a bi-axis system, with trees double budded in the nursery; and single axis. In-row tree spacings are 3 feet, 4.5 feet, or 6 feet, with 12 feet between the rows.
After two seasons, trees on Pyro-233 had smaller trunks than trees on other rootstocks. Individual axes of bi-axis trees, where the vigor is spread over the two axes, were half the size of single axis trees trained to other systems and had more flowers. Einhorn expects that as the trees grow, those planted with the closest in-row spacing will be more dwarfed because of inter-tree competition. •