Commercial fruit trees usually consist of two parts, the scion (the fruiting variety) which makes up most of the tree that you see above ground-level, and the rootstock which – as the name suggests – consists of the roots and lower portion of the trunk. The join or “union” is easy to spot in a young tree – it is the kink a few inches above the ground where the scion was budded or grafted on to the rootstock. This marriage works because rootstocks are very closely related to scions – thus apple rootstocks are apple varieties in their own right, but where the main attribute is not fruit quality but tree size. Plum rootstocks can also be used for apricots and peaches, which shows just how closely these species are related. Most rootstocks will produce edible fruit if left to grow naturally, but the fruit is usually small and poorly flavored.
The variety selected for the scion imparts the fruit characteristics such as size, color, and quality factors. The variety selected for the rootstock determines tree size, precocity, some disease resistance (such as fireblight) and even cold hardiness. And like the fruiting varieties, rootstocks also undergo breeding and selection for their desired characteristics. Whilst most scientific attention has focused on developing rootstocks for apple trees, rootstocks are also important for growing pears, plums and cherries.
The most common rootstocks used for apple, pear, and sweet cherry are listed below. Click on the crop heading to view the related rootstock information.
Pear Rootstocks
The majority of commercial pear trees are grown on rootstocks. Pear rootstocks impart characteristics such as vigor, precocity, disease resistance, and cold hardiness. The most commonly used rootstock worldwide is some selection of a Bartlett seedling, making it the “standard” rootstock. In rootstock trials, rootstock test scores are often expressed as a comparison to Bartlett characteristics. For example, the test rootstock may impart dwarf characteristics as 70% height compared to a Bartlett seedling tree. In North America, the most common Bartlett-type rootstock is OHxF. OH stands for “Old Home”, a name given to a seedling selection discovered in Illinois by Prof. F.E. Reimer of OSU. It was found to be resistant to fireblight, but was self-infertile. The “F” stands for Farmingdale, the town in Illinois that Reimer discovered the second Bartlett selection. Like OH, it had fireblight resistance, although not quite as good, but it was self-fertile. Old Home and Farmingdale were crossed by L. Brooks of Oregon and the resulting offspring were fireblight resistant, self-fertile, vigorous and had good cold hardiness, making it desirable as a rootstock and receiving a patent in 1960.
The graphic above illustrates the overall influence on tree size* by various rootstock combinations compared to a Pyrus pear seedling. Key to abbreviations and names: BM = P. communis series from Australia; Brossier = P. nivalis series from Angers, France; Fox = P. communis series from the University of Bologna in Italy; Horner = OHxF clonal series from D. Horner (Oregon nurseryman) and selections by OSU-MCAREC; OHxF = ‘Old Home x Farmingdale’ series; Pi-BU = Pyrus series from Germany; Pyro and Pyrodwarf = P. communis selections from Germany; QR = P. communis selections; ‘Adams’, ‘BA29’, ‘EMC’, ‘EMH’, ‘Sydo’ = Quince dwarfing rootstocks (require interstem for most pear cultivars).
Selections shown in gray text indicate antiquated selections no longer in commercial production.
Selections shown in purple text indicate possible susceptibility to pear decline.
*This general classification of tree size may vary for different cultivars due to cultivar/rootstock interactions.
This graphic was adapted from the article by Elkins, Bell, Einhorn, 2012, J. Amer. Pomol. Soc. 66(3):153-163.
Pear varieties growing on OHxF or any Bartlett seedling rootstock tend to be large, non-porous trees. In order to get trees that are more suited to high-density plantings, rootstocks with dwarfing traits and precocity need to be used. In many parts of the world, Quince selections are used as rootstocks. This combination will result in dwarfed growth and precocity. However, Quince is not compatible as a rootstock for many varieties of pear such as Bartlett, Bosc, Forelle, Packham, Triumph, Winter Nellis and Eldorado. For these varieties, the use of an interstock (intermediate graft section) must be used. Another problem with using Quince is that most varieties are not winter hardy making it a poor choice for the Pacific Northwest. However, there are ongoing trials at OSU testing potential Quince selections exhibiting good winter hardiness (Einhorn’s work).
Descriptions of some of the more commonly available pear rootstock.
All commercial cherry trees are made up of two parts: the upper fruiting portion (grafted or budded scion wood); and the lower portion ( the rootstock). Until fairly recently, the majority of breeding efforts were directed towards fruit improvement. Over the past century, breeding programs have concentrated mainly on achieving improved characteristics such as yield, taste, fruit size, fruit firmness, fruit color, precocity, and resistance to fruit cracking and disease. In contrast, rootstock development has only recently received breeders attention. It is believed that ‘Mazzard’ seedlings are the oldest known sweet cherry rootstock dating back to the early Greeks and Romans. And this is still the most widely used rootstock for sweet cherry throughout the Pacific Northwest. Many of the newer rootstocks are described using Mazzard as a standard for comparison. Recently, several new rootstocks have gained prominence for their improved attributes. Many of these are semi-dwarfing. Some of these may impart some disease resistance, induce precocity (bearing younger, and lend themselves to use in high-density plantings. There is an excellent PNW Extension publication by L. Long and C. Kaiser reviewing the performance of the major sweet cherry rootstocks grown around the region. (download pdf PNW619) Listed below are many of the sweet cherry rootstocks available for use in the Pacific Northwest.
- Relative size comparison chart of several rootstocks being evaluated by Michigan State University and Washington State University. More information about this graphic can be found in this Good Fruit Grower article.
Listed below are many of the sweet cherry rootstocks available for use in the Pacific Northwest. Click on the heading to view details about each rootstock.
