Rootstock Options
Written By:
Robert Crassweller, Ph.D. Professor of Horticulture & James Schupp, Ph.D. Professor of Pomology, Penn State University
History of Apple Rootstocks
Rootstocks to control tree size have been used in apple production for over 2,000 years. Historically, most of the clonal apple rootstocks that we use in the United States traditionally originated in Europe. In the mid-1800s horticulturists began referring to rootstocks by name. They were called Paradise (or French Paradise) or Doucin (or English Paradise), the former being more dwarfing than the latter. These plants, however, showed much variation in size control. In addition, many new stocks had been introduced inaccurately under these names; undoubtedly viruses and genetic mutations had occurred in the plant material. In the late 1800s one author described 14 different kinds of Paradise rootstocks. This diversity led researchers at England’s East Malling Research Station to gather the selections to determine their trueness to name. The researchers concluded that indeed there were numerous misnamed and mixed collections of plant material.
Platform Harvesting of 2-D Training System Employing Size Controlling Rootstock, New Zealand.
Dr. R. Hatton decided that because of the confusion he would drop the proper names and assign each stock a number. He as-signed a Roman numeral to each of 24 selections but did not number them in any order with respect to tree size. Hence, M.9 with a larger number is a smaller tree than M.2. Most of these, with the exception of M.9, M.7, M.2, M.8, and M.13, were never commercially important in the United States. In succeeding years some rootstocks were developed from controlled crosses, M.26 and M.27 being the most famous. In 1917 a second research station, the John Innes Institute of Merton, England, joined with the East Malling station to begin a breeding program. Their efforts, oriented mainly toward developing rootstocks resistant to woolly apple aphids, produced the Malling-Merton series of rootstocks, of which MM.106 and MM.111 are still used some today.
In the late 1960s, researchers began work to remove many of the viruses naturally present in the rootstocks in order to reduce incompatibility problems caused by the viruses. The first rootstock to be partially cleaned up was M.7; it was designated M.7a. Later still, more viruses were removed from all of the Malling and Malling-Merton series of rootstocks. These were then designated EMLA for the East Malling and Long Ashton research stations in England. While the viruses have been removed, some of the rootstocks’ size control has been lost. Therefore, the old “dirty” M.9 will produce a smaller tree than the “clean” M.9EMLA. Currently in the industry nearly all apple rootstocks are virus free.
More recent years have seen the introduction of several new rootstocks, many developed in Europe. The first to be available was the Budagovsky series. Designated as either Bud or B, they were developed in the central plains of Russia at Michurinsk College for their cold hardiness. Currently B9, B10 and B118, increasing vigor, are rootstocks that are available in the U.S. Work at Penn State showed that B9 had some resistance to fire blight. The next rootstocks that were released to be tested were from Poland and are called the “P-series.” Like the Russian series, they are expected to have some cold hardiness. The P-series was developed from crosses between M.9 and common Antonovka. These stocks have good resistance to collar rot. To date, only a limited number of these rootstocks are available.
A rootstock breeding program was started here in the United States at Cornell University and in cooperation with the USDA breeding program. The main characteristics they are looking to select for is resistance to fire blight, crown and root rots (Phytophthora sp., and replant disease complex.. Many of these rootstocks are also resistant to other problems such as apple scab, and woolly apple aphids, and exhibit a reduction in burr knot formation. Cornell has produced a comparison chart of all the Geneva rootstocks that is available as a PDF.
A large multistate research program known as the NC-140 Research Project is primarily responsible for conducting most evaluations of these new rootstocks. Penn State has been a member of this project since its inception in the late 1970s.
Growers should be aware of each rootstock’s known capabilities and limitations. Many of the newer rootstocks will probably be available to the commercial industry before they have been thoroughly evaluated with different cultivars.
Specific rootstocks
Rootstocks are listed in order from smallest to largest. Much of the information was gleaned from research reports of the NC-140 committee from around the country. More information and images of trees on the different rootstocks are available through the Penn State Extension website.
A very dwarfing rootstock. Unless the central leader is supported, the tree will be very small. Little is known about disease or insect susceptibility. To date, most commercial nurseries are using this rootstock only as an intermediate stem piece on MM.106 or MM.111. If handled and spaced properly, it can be a very productive stock for a vertical axe system.
Geneva 65 (G.65) was developed by Dr. Jim Cummins at Cornell University. Due to errors in tissue culture buildup of this rootstock, the U.S. distribution of this rootstock has been hindered. Tree size once thought to be about that of M.9 is now considered to be closer to M.27. The rootstock is difficult to propagate in nursery stool beds. It is susceptible to tomato ring spot virus and apple stem grooving virus.
Budagovsky 9 (B.9 or Bud9) is a new dwarfing rootstock bred in the Soviet Union from the cross of M.8 x Red Standard (Krasnij Standart). Like the other stocks in this series, the leaves are a distinctive red. Trees on this stock are 25 to 35 percent smaller than M.9EMLA depending on the cultivar. In a 10-year trial at University Park, York Imperial, Rome Beauty, and Empire on B.9 were approximately 25 percent smaller than the same cultivar on M.9EMLA; while Jonagold, Golden Delicious, and McIntosh were approximately 35 percent smaller. B.9 appears to be resistant to collar rot and is very cold-hardy. In limited trials, it has performed very well across a wide range of conditions. Trees will need to be supported.
The traditional and best-known dwarfing rootstock. It should be planted on a well-drained site. Trees on this rootstock always require leader support. The rootstock is very susceptible to fire blight and can develop burr knots. Numerous clones of M.9 are now being sold by nurseries, including M.9 NAKB 337, the current dominant strain used. It is a virus-free clone from the Netherlands and appears to be 5-10 percent less vigorous than M.9EMLA. M.9EMLA is a virus-free clone from the East Malling/Long Ashton research stations. It is approximately 25-30 percent more vigorous than M.9. Pajam 1 (Lancep) and Pajam 2 (Cepiland) are French selections that are relatively new. They are 35 to 40 percent more vigorous than M.9 NAKB 337. One other clone is M.9 RN 29, selected by Rene Nicolai in Belgium. In plantings at University Park with Gala, it is approximately 30 percent larger than M.9 NAKB 337.
Geneva 16 (G.16) was released from Cornell University’s breeding program. Like others in the series, it is resistant to fire blight. It is tolerant of crown and root rots. It is susceptible to woolly apple aphid and powdery mildew. Size was initially reported to be between that of M.9 and M.26. However, in a trial at Rock Springs with the scion cultivar of Golden Delicious at the end of the tenth growing season, it was approximately 20% smaller than trees on M.9T337 and 65 percent smaller than M.26. It does appear, however, to induce wider branch angles in the scion cultivar. Geneva 16 is very sensitive to latent viruses in apple and should only be propagated with virus free scion wood on top.
Geneva 41 (G.1) resulted from a cross between M.27 and Robusta 5 and was introduced by the New York State Agricultural Experiment Station. Geneva 41 and has been tested as CG 3041 and is a full dwarf, compared to M.9 NAKBT337 it is approximately 25% smaller and 50% smaller than trees on M.26EMLA. G.41 has higher yield efficiency and produces few root suckers. It is highly resistant to fire blight, wooly apple aphids and Phytophthora. Tests indicate that G.41 appears to be tolerant of replant disease. A major drawback to wider adoption of this rootstock is its tendency to form a brittle graft union with some scions especially Cripps Pink and Honeycrisp. Therefore, well branched trees need to be staked immediately after planting to prevent breakage due to high winds. G.41 is believed to be better suited to high pH soils.
Budagovsky 10 is a release from the Michurinsk University of Agriculture (Russia) breeding program, which is trying to select for improved winter hardiness. A 10-year trial in Pennsylvania with Golden Delicious as the scion cultivar showed that trees on this rootstock were similar in size to trees on G.935 and M.9 T337 (15 percent smaller). Main scaffold branch angle was close to 90 degrees. Production efficiency and total yield were slightly better than trees on M.9 T337. The rootstock is recommended for trials.
This rootstock was bred in Canada for its cold hardiness, from a cross between Robin crabapple x M.9. The rootstock roots poorly in stoolbeds and is often micropropagated. Trees on O.3 are about the size of M.9EMLA but smaller than M.26. Induces early bearing. Resistant to collar rot, but susceptible to fire blight and woolly apple aphids. Ottawa 3, although being available for many years, has not been popular with the nursery industry. Ottawa 3 is very susceptible to apple mosaic virus, so only material known to be virus free should be planted on this rootstock.
This rootstock came from the breeding program at the Vineland station in Ontario, Canada. Tree size is comparable or slightly larger than M.26. Yield efficiency and fruit size are equal to or greater than M.26. However, unlike M.26, it appears to be highly resistant to fire blight. It has good cold-hardiness.
A more vigorous rootstock than M.9. It can be used to produce either a dwarf or a semidwarf tree, depending on scion variety, production system, and soil type. It is susceptible to collar rot and fire blight and should not be planted in a wet site. Certain varieties, such as Rome, Stayman, Golden Delicious, and many triploids, when grafted onto this rootstock may exhibit signs of graft union incompatibility. When incompatibility occurs, the trees may break off at the union in high winds. Because exposed portions of the rootstock have a strong tendency to produce burr knots, the union between the scion variety and the rootstock should be set no more than 1 to 2 inches above the final soil level.
Geneva 214 (G.214) is a cross of Robusta 5 x Ottawa 3 and tested as CG.4214. Trees on this rootstock will need to be supported and produce a tree about 30-35% size of seedling with vigor and precocity similar to M.9 Nic.29 and M.26. Trees are more productive than those rootstocks and have good cold hardiness, and are resistant to fire blight, Phytophthora root rot and wooly apple aphid.
Geneva 935 (G.935) is a cross of Ottawa 3 and Robusta 5. Size is reported to be slightly larger than M.26, but the rootstock has resistance to fire blight and crown rot. It is not resistant to woolly apple aphid. Production efficiency is rated equal to M.9. In the Golden Delicious trial at Rock Springs at the end of the tenth growing season tree size was about 15 percent smaller than M.9. However, with the more vigorous Fuji tree size was comparable to M.9. Production efficiency was not significantly different although slightly higher than M.9. The rootstock seems to induce wider angled branching in the scion. Geneva 935 is sensitive to latent viruses in apple and should only be propagated with virus-free scion wood on top.is a cross of Ottawa 3 and Robusta 5. Size is reported to be slightly larger than M.26, but the rootstock has resistance to fire blight and crown rot. It is not resistant to woolly apple aphid. Production efficiency is rated equal to M.9. In the Golden Delicious trial at Rock Springs at the end of the tenth growing season tree size was about 15 percent smaller than M.9. However, with the more vigorous Fuji tree size was comparable to M.9. Production efficiency was not significantly different although slightly higher than M.9. The rootstock seems to induce wider angled branching in the scion. Geneva 935 is sensitive to latent viruses in apple and should only be propagated with virus-free scion wood on top.
Geneva 11 (G.11) is the second release of the Cornell breeding program; only limited plantings exist in Pennsylvania. In the 2007 Fuji trial G.11 was about 25% smaller than trees on M.9T337, but more productive. Has the advantage of being resistant to fire blight and crown rot as well as only rarely producing suckers or burr knots. Tissue-cultured trees are larger than trees propagated by stool beds.
Geneva 202 (G.202) is a semidwarfing rootstock that produces a tree slightly larger than M.26. It was developed from a cross of M.27 and Robusta 5. It is fire blight and phytopthora resistant as well as having resistance to woolly apple aphids. The rootstock has been mainly tested in New York and New Zealand. In New Zealand they are looking at this rootstock as a possible replacement for M.26 since it is more productive than M.26. In a 9-year study with the scion cultivar of Liberty, G.202 was about 50 percent smaller than M.7 but had much greater production efficiency.
Geneva 210 (G.210) is a semidwarfing rootstock that is resistant to fire blight (Erwinia amylovora) and crown rot (Phytophthora spp.). It is a hybrid from a cross between Ottawa 3 and Robusta 5, and is larger than Ottawa 3 but smaller than Robusta 5. It is similar in size to Malling 7 but more productive and precocious.
Geneva 890 (G.890) is a semi-dwarfing rootstock hybrid from a cross of Robusta 5 x Ottawa 3 and about 55 to 65 percent the size of seedling. It is resistant to fire blight (Erwinia amylovora), crown rot (Phytophthora spp.), and woolly apple aphid with good cold hardiness. Tree does produce rootsuckers but we have not seen any evidence of burr knot formation. Tree size is reported to be approximately the same as M.7 to MM.106, but with yield efficiency similar to M.9. Rootstock was released for use as a freestanding tree for processing orchards or as supported trees with weak scion cultivars.
Geneva 969 (G.969) is a semi-dwarfing rootstock hybrid from a cross of Robusta 5 x Ottawa 3. It is resistant to fire blight, crown rot, and woolly apple aphid with good cold hardiness. It is classified as having growth control similar to M.7. Honycrisp on this rootstock at Rock Springs produces the same size tree at the end of the end of the 5th growing season. The rootstocks produce few root suckers or burr knots. Suggested for trial for growers desiring a freestanding tree although NC-140 trials have all been with trees grown with support.
Pillnitzer Supporter 4 (Pi.80), a cross between M.9 and M.4, was introduced from Germany. It is reported similar in size and in anchorage to M.26. Yield capacity is reported to be better than that of M.26. A planting with McIntosh as the cultivar was established at Rock Springs. Supporter 4 grew to about 15 percent larger than M.7 EMLA. Yield was nearly double that of McIntosh/M.7EMLA and 50 percent greater than McIntosh/M.26EMLA.
This stock is composed of an understock such as seedling MM.111 or MM.106, onto which an intermediate stem piece of M.9 or M.27 is grafted. The variety is budded or grafted onto M.9 or M.27. Size control is directly related to the length of the intermediate stem piece. Interstem apple trees offer a strong root system while reducing the size of the overall tree. Interstem trees should be planted so that a portion of the interstem is buried. Test plantings in Pennsylvania indicate that interstems on either MM.106 or MM.111 sucker, and very vigorous varieties like Stayman have not performed well on interstems.
The advantages of this M.7-size rootstock are early production, fewer burr knots, and less suckering. Tests at Rock Springs do indicate that trees on this rootstock come into bearing earlier and produce more fruit than M.7. Unfortunately, questions have arisen about the graft compatibility of this rootstock with Gala. In tests around the country in the NC-140 trials, there have been occasions where Gala/G.30 have snapped off at the bud union during high winds. Therefore, it is recommended that if Gala is propagated on G.30, the trees be supported by two wires, one at approximately 36-40 inches above the ground and a second wire at 8-9 feet. Individual stakes or poles have not been sufficient because they allow excessive twisting of the trees in the wind.
This rootstock was developed from a cross of Robusta 5 x Malling 27.The semidwarfing rootstock is reported to be approximately 45-55% the size of seedling and needs to be supported. Trees on this rootstock are similar in vigor to M.7 but more precocious and productive with good cold hardiness; resistance to fire blight, Phytophthora root rot and wooly apple aphid.
This rootstock produces a semidwarf tree that is freestanding in deep well drained soils. In rocky, steep, or shallow soils, it tends to lean. High budding and deeper planting will help remedy this problem. The rootstock may sucker profusely and is susceptible to collar rot. M.7a is a clone of the original M.7 that has had some of the inherent viruses removed.
A rootstock, slightly larger than M.7, that produces freestanding, early bearing trees. Trees on MM.106 are susceptible to collar rot when planted in wet soils and are not recommended for poorly drained sites. Delicious on MM.106 is susceptible to apple union necrosis.
An older rootstock that is reappearing in nurseries and orchards. It produces a semidwarf to semistandard freestanding tree, depending on scion variety. Trees are strong, crop well, and do not have collar rot problems.
This stock holds the most promise for those wanting a larger tree about the size of MM.111. Its other advantages are tolerance to fire blight and resistance to collar rot. It will probably perform better in wet or heavier soils.
A well-anchored rootstock, resistant to woolly apple aphids, and tolerant of drier soil conditions. It is the most cold-hardy rootstock readily available. Trees on MM.111 are semistandard to standard in size. Planting depth of this rootstock is critical. The union should be no higher than 1 to 2 inches above the final soil line.
Budagovsky 118 (B.118) is a more vigorous clone out of the Minsk breeding program. It is more vigorous than the other rootstocks in the series but still imparts the high degree of winter-hardiness. It propagates easily in stool beds and does not sucker. It has moderate resistance to fire blight but is susceptible to Phytophthora. Because of the vigor of the rootstock it is only recommended for spur strains of apple or in weak soil or replant situations.
A rootstock from apple seeds, with a variable genetic makeup, suckering and disease susceptibility. Varieties on this rootstock produce the largest trees. Few nurseries that supply commercial fruit growers have trees grafted onto seedling for sale anymore.