Rootstocks for Fruit Trees in Wisconsin R-11-01

A3561

OOTSTOCKS FOR FRUIT TREES R IN WISCONSIN

ORDER TO OBTAIN Rootstocks may also be used fruit that is true to as interstems, a small piece type, fruit trees inserted between the are propagated rootstock and scion in INby budding or graft- the propagation ing sections of process. These trees known cultivars are known as “three- (scions) onto special piece” trees. Interstems rootstocks. This creates reduce the high vigor fruit trees composed of of otherwise desirable two parts: a scion (culti- rootstocks. var) and a rootstock. Many Some rootstocks are nurseries now offer trees with a more susceptible to dis- choice of several root- eases or insects than stocks. In this way others. Disease resist- growers may choose the ance is a major com- particular scion/rootstock ponent of rootstock combination that is suited breeding programs. to their needs. This bulletin Rootstocks may also pro- describes the various rootstocks vide some degree of tolerance to available for fruit crops that can be successfully soils that are sometimes too wet or too dry. grown in Wisconsin.

Rootstocks play an essential role in determining orchard performance. They are responsible for TYPES OF ROOTSTOCKS water and mineral uptake and provide anchorage Rootstocks are classified according to tree size for the tree. and how they are propagated. We commonly refer to rootstocks as dwarfing, semi-dwarfing, or Rootstocks may be winter hardy or cold tender. If standard, an indication of tree size for cultivars the rootstock is killed by cold winter tempera- propagated on a particular rootstock. Smaller tures the scion will leaf out in the spring, but as trees are more efficient, more productive, and soon as temperatures warm up, the entire tree more precocious than their larger counterparts. will die. Only winter-hardy rootstocks should be planted in Wisconsin. Rootstocks may be propagated by either asexual or sexual means. Asexually (or vegetatively) Rootstocks determine tree size. Small trees are propagated rootstocks, known as clonal root- more efficient and may be planted closer together stocks, are produced via cuttings, stooling, or tis- in the orchard. The rootstock has a great effect on sue culture. These stocks are genetically uniform. how soon a tree begins to produce fruit. Dwarf Sexually propagated rootstocks are produced trees will bear fruit earlier than large trees. from seed. They are known as seedling or stan-

T ERYL R. ROPER ootstocks for fruit trees RIN W ISCONSIN

dard rootstocks and are not genetically uniform. in the late 1800s European orchardists recognized Each propagation method has its advantages, and the possibilities of smaller trees for commercial one type should not be rejected for its propaga- orchards. tion method alone. Indeed, most stone-fruit root- stocks come from seed. The initial period of commercial use resulted in substantial confusion as new size-controlling root- Each type of fruit has its own particular root- stocks were introduced with the same names as stocks. Generally, the rootstock must be of the older materials and the older stocks acquired same genus as the scion in order to produce a many different local names. Beginning in 1912, successful graft. workers at the East Malling Research Station in England collected and catalogued many of the BEFORE THE EARLY 1950S MOST dwarfing rootstocks throughout Europe and apple trees sold in North Great Britain. In 1917 the first of these rootstocks America were propagated on were released, designated with the Roman seedling rootstocks. These numerals M.I to M.IX (they have since been rootstocks were produced from renamed using arabic numbers). Also in 1917 the APPLES seeds of apple cultivars Malling Immune series (MI) was introduced, expected to be vigorous, win- although none of these stocks ever came into ter hardy, or disease resistant wide usage. In 1952 the Malling-Merton (MM) or to have other desirable hor- apple rootstock series was released. These root- ticultural traits. Trees produced stocks, designated MM.101 to MM.115, are resist- this way were highly variable ant to woolly apple aphid. Additional work at the and the trees were large, slow to bear, and diffi- East Malling station led to the introduction of the cult to manage. Since the late 1950s clonal dwarf Malling rootstocks through M.27, which is the last and semi-dwarf trees have become popular. to have been released from that program.

As early as the late 1500s gardeners observed that Virus-infected rootstocks can transmit viruses to some apple and pear trees were smaller than oth- the scion. All of the early size-controlling root- ers. The roots of these trees were propagated and stocks were virus infected. The East Malling and apple scions grafted onto them. At first this tech- Long Ashton Stations cooperated to remove nique was only used in small private gardens, but viruses from the rootstocks. These were subse-

Figure 1. Relative size of apple trees propagated on clonal apple rootstocks. 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 Percent of standard tree size 10 10 0 0 M.27 M.9/B.9 M.26 G.30 MM.106 MM.111 2 quently introduced in the late 1950s and early Many clones of M.9 have been identified that 1960s. They were identified as M.7a, M.9a, etc., vary in size. The most common clone used in which are partially virus free, and EMLA 7, North America is NAKBT 337. Other common EMLA 9, and EMLA 27, etc., which are free of all clones include RN29, Pajam 1 and 2, and Flueren known viruses. Eliminating viruses from these 56. Nurseries typically don’t indicate what clone stocks increased their vigor by 10–15%. they are using, but the information can usually be obtained by asking. Apple rootstocks can be divided into four size categories: dwarfing, semi-dwarfing, semi-vigor- Budagovsky 9—This rootstock is frequently ous, and vigorous. While these size classes are called Bud.9 or simply B.9. It originated in central not absolute, they will give some indication of Russia and is very cold hardy. B.9 is similar to final tree size (figure 1). The scion also has a great M.9 in dwarfing characteristics, susceptibility to effect on final tree size. Vigorous cultivars will fire blight, and brittleness of roots (both root- produce larger trees than cultivars with a strong stocks require staking). Tests in Wisconsin sug- spur-type growth habit. gest that it is slightly larger and slightly less pro- ductive than M.9. The biggest advantage of B.9 is The following sections provide summary infor- its superior cold hardiness. B.9 is recommended mation on rootstock characteristics that should for orchards in areas with more severe climates apply to most areas in Wisconsin. Apple root- where root hardiness is essential. stocks are listed in order of increasing size. Ottawa.3—Sometimes designated O.3, this root- Dwarf stock is also hardy and equally productive to B.9. M.27—This is the most recent and the smallest of Its roots are not as brittle. The major drawback is the Malling clones. M.27 is very dwarfing, often that it is difficult to propagate in stool beds. As a producing a bush rather than a tree. Trees on result, it is difficult to find trees grafted onto O.3. M.27 are only 15–20% of seedling size. It typically Semi-dwarf is not used in commercial orchards in Wisconsin because it is too low in vigor. Its use may increase M.26—Mature trees on M.26 are 40–50% of in the future as low-vigor, high-density planting seedling size. After its introduction in 1959, M.26 systems are developed. Trees on M.27 must be became very popular because of its size and pro- staked at planting, as they are poorly anchored. ductivity. M.26 produces a freestanding tree, is well anchored, and has enough vigor that it usu- M.9 —This is one of the original East Malling ally does not runt out. However, it may benefit introductions. It is the most dwarfing rootstock in from some type of support. It is the most cold use in Wisconsin today and the most common hardy of all Malling introductions now used dwarfing rootstock in use worldwide. M.9 pro- commercially. It does not sucker readily. M.26 duces a tree about 25 to 35% of seedling size. It is will not tolerate wet soils and is susceptible to precocious, sometimes bearing fruit the year after crown rot and highly susceptible to fire blight. A planting. However, these fruit should be virus-indexed EMLA 26 was introduced in 1969. removed to avoid runting out the tree (stopping M.26 is recommended for medium-density vegetative growth). M.9 is recommended for high- orchards under either standard or moderate spur- density plantings because it is both productive type cultivars in Wisconsin. and precocious.

Roots of M.9 are brittle and break easily, so these trees should be staked or supported on a trellis immediately at planting. M.9 will produce suck- ers but not in large numbers. It is susceptible to fire blight. 3 ootstocks for fruit trees RIN W ISCONSIN

G.30—This is a new introduction from Cornell Vigorous University. G.30 is usually somewhat larger than Seedling or standard—Trees on apple M.26, but is far more productive. G.30 is a free- seedlings were the basis for Wisconsin’s apple standing tree and will not require any sort of industry until the late 1950s. Less than 2% of the support, although a single stake may be benefi- apple trees planted in commercial orchards in the cial during training. This rootstock is also resist- past 5 years in Wisconsin have been on seedling ant to fire blight. It has been hardy in the coldest roots. Seedling rootstocks produce large, vigor- test sites. Gala/G.30 has a weak graft union and ous trees that are freestanding, are well rooted, is not a good combination. G.30 is recommended and have delayed fruiting. However, consider- for medium-density orchards under standard or able variability is apparent among all of these moderate spur type cultivars in Wisconsin, espe- traits in seedling trees. Because of their low to cially those that are fire blight susceptible. moderate productivity and lateness in bearing M.7—Trees on M.7 are 55–65% of seedling size. (poor precocity), seedling trees are NOT recom- M.7 was one of the original Malling rootstocks. It mended for planting in Wisconsin. originated in France and was known as Doucin. New rootstocks It has been one of the most widely used root- stocks in the U.S. apple industry since clonal Several apple rootstock breeding programs are rootstocks became popular. It is widely adapted active around the world. Several rootstocks are to many soil types and climates and is very dis- currently under trial in various states under the ease tolerant. M.7 trees are freestanding and auspices of the NC-140 regional project. should not need support. However, M.7 is slow Wisconsin participates in this project. The pur- to bear and suckers readily. The full array of M.7 pose of this project is to evaluate new and prom- trees are available as M.7 (has viruses), M7a ising rootstocks before they are available in the (some harmful viruses removed), and EMLA 7 commercial industry. Thus far the NC-140 project (all known viruses removed). M.7 is recom- has identified some problems with new root- mended for medium-density orchards under less- stocks. These data allow nurseries and growers to vigorous standard or spur-type cultivars in decide whether these rootstocks have commercial Wisconsin. value in North America.

Semi-vigorous The breeding program at Cornell University is perhaps the most active. Several new rootstocks Two semi-vigorous rootstocks—MM.106 and in both the dwarf and semi-dwarf size categories MM.111—are available for Wisconsin but are not will be released over the next several years. Not recommended except for poor sites with infertile, all will be commercial successes, but they will rocky soils. They may also have value if replant- broaden the choices growers have when planning ing trees onto orchard land that has not been new plantings. There have been some problems allowed to lie fallow or been fumigated following with misnamed or mislabeled plant material tree removal. These rootstocks are too vegeta- coming out of this project, but these problems tively vigorous and are not precocious. Although have largely been resolved. nurseries still propagate trees on these rootstocks they are far less popular now than they were a decade ago.

4 FEWER ROOTSTOCK CHOICES Old Home x Farmingdale clones—These are available for pears than clones show a wide range of diversity in tree size for apples. Most apple cul- and vigor. They all have at least two characteris- tivars and rootstocks are of tics in common that make them acceptable for PEARS the same genus and Wisconsin: they are winter hardy and resistant to species (Malus x domestica), fire blight. There has not been wide experience while pear rootstocks are with these clones in Wisconsin, so they should be from several genera. planted for trial only.

Desirable pear rootstocks Clones of Old Home x Farmingdale should be resistant to fire Rootstock Description blight, be cold tolerant, OHxF 51 Dwarfing control tree size, and be compatible with a wide range of cultivars. So far no pear rootstock has OHxF 97 Vigorous been found with all these characteristics. In the OHxF 333 Semi-dwarfing past most pear rootstocks were Bartlett seedlings (Pyrus communis). Seeds were typically obtained Quince seedlings or clones—Seedlings of from cannery waste. Seedlings of other Pyrus quince (Cydonia oblonga) have been used for species have also been used. many years to give some size control for pears. Characteristics of individual pear rootstocks fol- Quince is not compatible with all pear cultivars. low, listed from most commonly used to least Trees on quince are somewhat smaller than on commonly used. Not all rootstocks listed are domestic pear and are precocious and efficient. suited to Wisconsin conditions. All quince rootstocks are winter tender and highly susceptible to fire blight. Quince should Pyrus communis seedling—Domestic pear not be used as a pear rootstock in Wisconsin. seedlings are still the most acceptable rootstocks for pear cultivars in terms of vigor, hardiness, ROOTSTOCK SELECTIONS and compatibility. These trees are adapted to a for tart cherry are lim- wide range of soil types and climatic conditions. ited. Commercial Trees on pear seedlings are well anchored and cherry plantings in strong. However, all pear trees on seedling roots TART Wisconsin are prima- are susceptible to fire blight. Pear trees on domestic rily ‘Montmorency’ seedling roots are recommended for Wisconsin. CHERRY on Mahaleb (Prunus mahaleb) seedling Pyrus calleryana seedling—Seedlings of rootstocks. Mahaleb is Pyrus calleryana are adapted to many soil condi- slightly smaller than tions and produce semi-vigorous growth. Pyrus Mazzard (Prunus calleryana is very resistant to fire blight, but it is avium) and is more not sufficiently winter hardy for Wisconsin. winter hardy. Several new clonal cherry root- Pyrus calleryana seedlings are not recommended stocks are now available, but for tart cherries for Wisconsin. these have few advantages over Mahaleb. Pyrus betulaefolia seedling—Seedlings of Following is a brief description of tart cherry Pyrus betulaefolia are also adapted to many soils rootstocks. and conditions. The trees are vigorous, larger Mahaleb—Prunus mahaleb is native to Asia than Bartlett seedling, and moderately tolerant of minor and southeast Europe. Mahaleb is pre- fire blight. Pyrus betulaefolia is winter hardy but ferred for dry sites and cold areas. It is a vigorous has not been widely tested under Wisconsin con- stock producing full-sized trees. Mahaleb is the ditions. Pear trees on Pyrus betulaefolia are rec- rootstock of choice for tart cherries in Wisconsin. ommended for trial in Wisconsin. 5 ootstocks for fruit trees RIN W ISCONSIN

Mazzard—Prunus avium, or bird cherry, is also usually large, so size control is not as important native to Europe and Asia minor. This is the as with other tree fruits. Myrobolan seedling is same species as sweet cherry. Mazzard is not as winter hardy, and it will tolerate a wide range of cold hardy as Mahaleb, but it will tolerate poorly soils except extremely heavy soils. Its greatest drained soils better than Mahaleb. Mazzard may drawback is its variability. Myrobolan is recom- be an acceptable rootstock in warmer sites with mended for plums in Wisconsin. less-well-drained soils in Wisconsin. APRICOT SEEDLINGS ARE USED Gisela series—These stocks were developed in almost exclusively as root- Germany and have recently been introduced into stocks for apricot scions. commercial trade. Their chief advantage is size Sometimes peach seedlings control; their greatest drawback is their need for APRICOT are used, but incompatibil- support. These stocks are primarily used to ity problems can occur, reduce the size of sweet cherry trees. Since tart and peach seedlings are cherries are mechanically harvested these stocks not winter hardy. Apricots are of little advantage (see table below). grafted on peach seedlings are not recommended in EUROPEAN AND Wisconsin. Most apricot American plums may trees in Wisconsin are on be grown successfully Manchurian or other apricot seedlings. Apricot PLUM in Wisconsin. Japanese seedlings are recommended for use as apricot plums are not suffi- rootstocks in Wisconsin. ciently cold hardy. Rootstocks must pro- vide cold hardiness and SELECTING A ROOTSTOCK productivity as well as Rootstocks are an important component deter- be compatible with all mining orchard production. You should match cultivars. Most plums the rootstock to your specific orchard characteris- have been grafted onto plum seedlings. tics. While choices are limited for pear and stone- Myrobolan seedling—Most European plum fruit growers in Wisconsin, all orchardists should cultivars can be grown successfully on consider the following factors when selecting a Myrobolan seedling rootstocks (Prunus cerasifera). rootstock. It is the most widely used plum rootstock in North America because it is easily propagated and provides good anchorage. Plum trees are not

GiselaG tart cherry rootstock clones Size Rootstock (% of Mazzard) Description

Gisela 1 (GI 172-9) 25 Productive and precocious, but sensitive to viruses. Not currently recommended. Gisela 5 (GI 148-2) 45 Productive and precocious. Produces wide crotch angles and is cold hardy. Tolerates heavy soils and viruses. Gisela 7 (GI 148-8) 50 Heavy bearing, well anchored, but support is suggested. Sensitive to Prunus necrotic ringspot virus. Gisela 6 (GI 148-1) 60 Semi-dwarfing, well anchored and adapted to a wide variety of soils, including heavy soils. Resistant to common cherry viruses. test 6 Orchard design Availability Tree spacing and tree density should be the first In the past, many orchardists selected rootstocks considerations when selecting a rootstock. If you based on nursery availability. The resulting mis- are planting a high-density apple orchard takes in orchard design decreased production (>500 trees per acre), then you must use a full and income potential. In most instances it is dwarfing rootstock. Medium-density orchards desirable to wait for the trees you want or to (100–500 trees per acre) may use either semi- have trees custom budded rather than accept dwarf or semi-vigorous rootstocks, depending on whatever is available. You will need to allow 2 to density. Low-density orchards (<100 trees per 3 years for delivery of custom budded trees. acre) may use semi-vigorous or seedling root- stocks. Trees that are planted too close together and are too vigorous will shade each other, PROPER CARE reducing fruit yield, size, and quality. For rootstocks to produce the desired result, they must be handled properly in the nursery and the Scion orchard. The scion must be budded onto the root- stock at the proper height. For apples and pears Strongly spur-type apple cultivars must have a on dwarfing rootstocks, low budding is preferred more vigorous rootstock than standard cultivars. to avoid burr knot problems. Trees on dwarfing Spur-type cultivars planted on dwarfing root- rootstocks must be planted with the graft union stocks produce little vegetative growth and little 2–3 inches above ground, because the dwarfing fruiting wood (runt out), thus producing few, effect of the rootstock will be lost if the scion is small fruit of poor quality. On the other hand, a allowed to root. Trees on seedling rootstocks very dwarfing rootstock will control the growth should be planted with the graft union about 1–2 of a very vigorous cultivar. inches below ground to strengthen the graft The scion must be compatible with the rootstock, union. especially for stone fruits. Reputable nurseries Although good anchorage is desirable for root- should be able to indicate incompatibility prob- stocks, it is not always achieved, particularly in lems before the trees are propagated. the most dwarfing rootstocks. Apple trees on dwarfing rootstocks (M.27, M.9, Mark, and M.26) Cold hardiness and cherry trees on Gisela rootstocks should be Both the scion and the rootstock must be able to staked or otherwise supported at planting. Trees survive harsh Wisconsin winters. This is a major on other rootstocks also benefit from staking. limiting factor on the types of tree-fruit crops that can be grown in the state. The relative cold hardi- ness of the major apple and pear rootstocks is CONCLUSION indicated in the previous descriptions. Stone-fruit Because rootstocks play a large role in tree physi- rootstocks are generally less hardy than apple ology, selecting the right rootstock is critical. and pear rootstocks; only the hardiest stone-fruit Apple and pear growers have more rootstocks rootstocks should be used. Peach seedlings are from which to choose, but selecting the right sometimes used as rootstocks for apricot and rootstock is also important for stone-fruit grow- plum, but are not recommended for Wisconsin. ers. Proper orchard management is required regardless of the rootstock selected. Good man- agement can never fully compensate for poor rootstocks, nor will good rootstocks perform to their potential with poor management.

7 ootstocks for fruit trees RIN W ISCONSIN

rootstock —the trunk or root material onto LOSSARY buddingG which buds or scions are inserted in grafting or —a method of grafting in which a single budding. bud is inserted into a rootstock or interstem. The runt out —a low-vigor condition characterized bud retains the characteristics of the original by cessation of vegetative growth and by small plant. burr knot fruit size. —roots that form in the bark of the scion —a piece or cutting of a twig, shoot, or above-ground portion of a rootstock shank. These small limb of the cultivar which is inserted into roots eventually break through the bark and die, the rootstock to form a union or graft. Also, the leaving a mass of dead tissue that may eventu- above-ground portion of grafted trees. ally girdle and kill the tree. seedling rootstock clone —a rootstock produced —plant materials that have specific charac- from seed via sexual propagation. teristics which are maintained by asexual (vege- seedling tree tative) propagation. Clones are produced by cut- —a tree on which the scion is tings, grafting, stooling, or tissue culture. propagated onto a seedling rootstock. The root- cultivar stock is produced by sexual propagation. See —a contraction of cultivated variety. standard tree. This term replaces the term variety. Cultivar is semi-dwarfing rootstock used instead of variety to avoid confusion with —a rootstock pro- botanical varieties. ducing a mature tree roughly 40–70% the size of dwarfing rootstock the same cultivar grafted to a seedling rootstock. —a rootstock producing a Typically propagated by vegetative means. mature tree roughly 25–40% the size of the same spur type cultivar grafted to a seedling rootstock. Typically —apple trees that bear fruit on short propagated by vegetative means. shoots called spurs. Trees are slightly smaller grafting than standard cultivars. —a method of propagating in which a standard tree small scion is placed in close cambial contact —a tree growing on a seedling with another stem so that the two grow together, rootstock. forming a new plant. stool interstem —shoots that originate below ground and —a piece of stem that is inserted become rooted. A method of vegetative propa- between the rootstock and scion, making a three- gation. piece tree. Dwarfing interstems can control tree size similarly to dwarfing rootstocks. precocious —bearing fruit at a young age, quick to bear fruit.

©2001 University of Wisconsin-System Board of Regents and University of Wisconsin-Extension, Cooperative Extension. Author: T.R. Roper is professor of horticulture, College of Agricultural and Life Sciences, University of Wisconsin- Madison and University of Wisconsin-Extension, Cooperative Extension. Produced by Cooperative Extension Publications, University of Wisconsin-Extension. University of Wisconsin-Extension, Cooperative Extension, in cooperation with the U.S. Department of Agriculture and Wisconsin counties, publishes this information to further the purpose of the May 8 and June 30, 1914 Acts of Congress; and provides equal opportunities and affirmative action in employment and programming. If you need this material in an alternative format, contact the Office of Equal Opportunity and Diversity Programs or call Cooperative Extension Publications at 608-262-8076. This publication is available from your Wisconsin county Extension office or from Cooperative Extension Publications. To order, call toll free 877-WIS-PUBS (947-7827) or visit cecommerce.uwex.edu A3561 ROOTSTOCKS FOR FRUIT TREES IN WISCONSIN R-11-01