What is a rootstock?

Visitors to my garden this time of year are often astonished to see me lopping the tops off some of my trees.

No, I’m not the Henry VIII of horticulture, chopping the head off any tree that no longer meets my fancy. OK, I am actually lopping the head off any tree that doesn’t meet my fancy.

I part ways with Ol’ Henry, though, because first, lopping the head off a tree does not kill it, and second, I graft on a new head. A few years after this seemingly brutal operation, the tree looks as chipper as ever. And it has a head that I like better — or else off it comes again.

I do this type of grafting, called topworking, mostly on my apple trees, but it could be applied to many other kinds of fruit or ornamental trees.

For instance, if you don’t like the growth habit of your red maple or the leaf shape of your Japanese maple, you can just lop back the head and change it. Same goes for the flower colour of a crab apple or flowering cherry.

Each time I lop back one of my apple trees, I can make that tree into any one of the more than 5,000 other varieties of apple.

Mostly, you can only graft the same kinds of plants together — any variety of apple on an apple trunk, cherry on cherry, maple on maple, etc.

GATHER YOUR STEMS

Before you can topwork any tree, you have to have stems, called scions, of the variety to which you want to change the plant. You might get scions from a neighbour’s or friend’s tree that you have admired. I often get scions for grafting mailed to me from enthusiasts elsewhere across our fruited plain, or from government institutions.

Healthy portions of last year’s growth, each cut into pieces a foot or so long, are ideal to become scions. They can be collected anytime in winter or early spring, as long as stems are showing no signs of growth and temperatures are above freezing.

Once you have scions in hand, put them in the refrigerator. Wrap them well in plastic, perhaps with a damp cloth to keep them plump with moisture.

A FEW CUTS AND YOU’RE FINISHED

The ideal time for topworking is when buds on the trunk are just beginning to grow; the scions are still under refrigeration in their winter sleep. This way, the scion will have time to knit to the lopped-back trunk and hook up its plumbing before its buds expand into thirsty new shoots.

The actual grafting operation is simple, and there are a few ways to go about it. The method I’ll describe is the cleft graft, practised by gardeners for thousands of years and best done on trunks 2.5 to 10 centimetres across.

Wedge grafting and bark grafting are among other methods of topworking, described in such books as The Grafter’s Handbook by R.J. Garner (Sterling Publishing, 1993) and Plant Propagation: Principles and Practices by H. Hartmann, D. Kester, F. Davies and R. Geneve (Prentice-Hall, 2010), and are useful with trunks even 30 centimetres across.

After lopping off the tree’s head and squaring off the top of the trunk with a clean saw cut, begin the cleft graft by hammering the blade of a heavy knife right down into the stub to form a five or 7.5-centimetre split. Remove the blade and let the split close up.

Next, cut two scions to fit into the split in the trunk. Do this by slicing wood from the bottom five to 7.5 centimetres on either side of each scion, making that bottom portion wedge-shaped in cross section, but slightly asymmetrical. (You “plant” more than one scion into the trunk when topworking as insurance against failure; a couple of years later you prune to leave only the one that made the best growth.)

Now, force a screwdriver into the middle of the slit in the trunk to open it up, and slide each scion into each of the outer edges of waiting gap. The better the alignment of the line between the bark and wood on each scion with this same line on the trunk, the better the healing, because the layer just beneath the bark is the source of all new cells at the graft.

Once scions are snuggled in place and aligned, remove the screwdriver to let the split close up and firmly hug the two scions.

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DRYING IS YOUR ENEMY

If your timing is right, and trunk and scions are in good contact, the only remaining threat to success is from the cut ends drying out. Avoid this by thoroughly coating all cut surfaces, including the tips of the scions, with some sort of pruning paint or grafting wax. My favourite is a gooey black stuff called “Treekote.”

Check the graft a day after the operation to make sure all surfaces are still thoroughly sealed. Then stand back, because with an established root system it’s possible to get a metre or more of growth from a scion in one season!

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Efficient Rooting System for Apple “M.9” Rootstock Using Rice Seed Coat and Smocked Rice Seed Coat

Abstract

“M.9” rootstock is considered as one of the most useful apple (Malus x domestica Borkh.) rootstocks; it produces dwarfing trees efficiently. As “M.9” rootstock shows a poor, brittle, and shallow roots system, we grafted “M.9” rootstocks onto “Marubakaidou” (M. prunifolia Borkh. var. ringo Asami Mo 84-A). We then propagated them by mound layering to establish a high-density root system. It was found that covering the roots with rice seed coat (RSC), RSC + smoked rice seed coat (SRSC), and vermiculite during mound layering was effective for the initiation of rooting. Utilizing RSC and SRSC seemed especially effective for producing “M.9” roots efficiently.

1. Introduction

Apple (Malus x domestica Borkh.) is the second most significant cultivated fruit tree (80.82 million metric tons were produced in 2013) worldwide after banana . Rootstocks of apple trees are usually used to propagate apple cultivars, and clonal rootstock is propagated by asexual or vegetative propagation, such as cutting and tissue culture . There are two series of clonal apple rootstocks: East Malling (EM) and Malling Merton (MM), both of which are virus-free and possess size-controlling characteristics . The clonal apple rootstocks consist of three distinct types based on the tree sizes of scions (cultivars): dwarf-type “M.27,” “M.9,” and “M.26”; semidwarf-type “MM.106,” “MM.104,” “M.7,” “M.4,” and “M.2”; and no dwarf-type “MM.111,” “MM.109,” and “M.10” .

In this study, we focused on “M.9” rootstocks because apple growers desire dwarf apple trees with high quality fruits that can be reaped easily and safely, especially at harvest time . However, the “M.9” rootstock has a problem with poor, shallow, and fragile root production. Although the rooting of “M.9/29” was improved greatly by its transformation with the rolB gene from Agrobacterium rhizogenes , the transgenic apple seems to difficultly obtain government permission or public understanding, especially in Japan. On the other hand, layering is the method used for root propagation in which a portion of stem or limb grows roots while still attached to the mother plant, and it is the useful propagation method for the clonal rootstock of “M.9” . For obtaining the “M.9” roots more efficiently, we investigated the effectiveness of rice seed coat (RSC), smoked rice seed coat (SRSC), and vermiculite for the “M.9” root production.

2. Materials and Methods

2.1. Plant and Covering Material

The experiment was conducted in 2013 and 2014. The rootstocks “M.9” Nagano (ACLSV-free) and “Marubakaidou” (M. prunifolia Borkh. var. ringo Asami Mo 84-A) from Nagano Fruit Experimental Station were used as scions and stocks, respectively. Both scions and stocks were selected from one-year-old branches.

Rice seed coat (RSC) and smoked rice seed coat (SRSC) were obtained from the Experimental Farm of TOGO field in Nagoya University and Kinahta Mizunami Shop in Mizunami City, Gifu, Japan. The vermiculite was obtained from Asian Seed Co., Ltd., Japan.

2.2. Grafting and Layering of “M.9” Rootstock

Bark grafting for “M.9” Nagano scions and “Marubakaidou” stocks was conducted in March at Nagano Experimental Station. They were planted in ten columns and seven rows with 50 cm and 100 cm spaces between plants and rows, respectively, at the experimental field in Nagoya University.

For mound layering, the grafted “M.9” Nagano rootstocks (5 and 65 in 2013 and 2014, resp.) were covered with RSC (two and 15 in 2013 and 2014, resp.), SRSC (two and 10 in 2013 and 2014, resp.), 50%  ×  50% mix of RSC and SRSC (R + S) (10 in 2014), vermiculite (10 in 2014), and soil and with no cover (control) (one and 10 in 2013 and 2014, resp.), when their height exceeded 3 cm. A week after the covering, all of the rootstocks including control were covered by soil, especially when their height exceeded 10 cm, and covering with soil extended until they were 30 cm tall.

2.3. Digging and Measurement of “M.9” Rootstock

Digging out one or two of each of the grafted “M.9” rootstocks was carried out on the 22nd of June, August, and October 2014 and backfilled. Finally, all the grafted “M.9” rootstocks were dug out on the first of December, 2014. After digging them out we measured the number, length, diameter, and the fresh and dry weight of the roots, which appeared from the covering material layer.

3. Results and Discussion

3.1. Root Initiation of “M.9” Nagano

We collected “M.9” Nagano and “Marubakaidou” rootstocks at Nagano and then grafted “M.9” Nagano as scions on the next day at Nagoya University in 2013, but all the grafted “M.9” rootstocks died after being covered with RSC, SRSC, or soil (results not shown). The rootstocks seemed to have lost their freshness and the amount of their callus, which plays a critical role in graft union before grafting. As the timing of grafting seemed to be important, we collected both rootstocks and grafted them on the same day in Nagano in 2014. All grafted “M.9” rootstocks grew well except for three rootstocks covered by SRSC. SRSC seemed to have strong water-leaching ability; therefore, those rootstocks might have died from being dried out. To solve the problem, we changed the watering schedule from once to twice per 24 hours.

Newly generated roots were obtained on the 22nd of June at rootstock sites covered with RSC, R + S (RSC + SRSC), and vermiculite; however, no roots were induced with SRSC, soil, or control (Figure 1). The greatest number of roots was produced by R + S. Generally, development and growth of roots were strongly affected by soil texture, moisture, fertility, and aeration . As soil and control (covered by soil one week after) conditions are heavy compared to RSC, RSC + SRSC, and vermiculite conditions, the “M.9” rootstocks covered by soil seemed to damage healthy buds before root initiation. RSC, RSC + SRSC, and vermiculite affected the bud stem colors of “M.9” rootstocks and changed them to yellow or yellowish, which might induce root initiation early. In case of SRSC, the water supply seemed to cause a depression of the SRSC layer when covered by soil. Therefore, roots were not observed in June; however, the roots of the same degree as RSC, RSC + SRSC, and vermiculite were produced on the 22nd of August and October (results not shown). Although the initiation of rooting was delayed at RSC covering, rooting efficiency including root numbers and weight seemed to be recovered from its fertilizer effect. Similar timing of “M.9” root growth initiation has been reported by Psarras et al. .

Figure 1 “M.9” roots produced after one-month treatment of rice seed coat (RSC), smoked rice seed coat (SRSC), combined 50% RSC and 50% SRSC (R + S), vermiculite (Verm.), soil (Soil), and no soil (Cont.).

3.2. Root Generation of “M.9” Nagano

Generalized root numbers were significantly higher in RSC (/plant) and SRSC (/plant) than in control (/plant) on the first of December (Figure 2(a)). The number of roots was also higher in R + S, vermiculite, and soil than in control but not significantly (Figure 2(a)). Tamai et al. reported that “M.9” Nagano rootstock that produced roots by mound layering lost the colors of young shoots (etiolating) and that the average root numbers per shoot were about 10 when harvested from 3- to 5-year-old stool bed. The average root numbers increased twice by utilizing RSC and SRSC (Figure 2(a)). The combination of etiolation and banding shading increased rooting significantly; in fact, “M.7” and “MM.106” clonal rootstocks produced significantly higher roots under dark treatments than those that were treated by persistent light . Higher root numbers from RSC and SRSC covering than from those of other materials might have been caused by the effective etiolation of buds by shading (Figure 2(a)).

(a)
(b)
(c)
(a)
(b)
(c) Figure 2 Number (a), dry (b) and fresh weight (c) of “M.9” roots per plant which appeared after 6-month treatment with rice seed coat (RSC), smoked rice seed coat (SRSC), combined 50% RSC and 50% SRSC (R + S), vermiculite (Verm.), soil (Soil), and no soil (Cont.). Values represent the means ± SE of 4 or 7 plants, and those with different letters differed significantly at by one-way anova followed by Dunnett’s multiple comparison test.

Regarding fresh and dry weight of roots, SRSC and R + S brought about heavier weight than those of the control (Figures 2(b) and 2(c)). Concerning root length and diameter, however, we could not detect any significant differences among the treatment materials (results not shown). Before use, SRSC was changed from nonorganic (RSC) to organic material (ash), which had dark colors and contained more fertilizer. Therefore, SRSC and R + S containing ash and a half of SRSC ash, respectively, brought about heavier root fresh and dry weights than the control (Figures 2(b) and 2(c)). Vermiculite contains no fertilizer, and it seemed to therefore produce poor roots among the treated materials (Figures 2(b) and 2(c)).

4. Conclusions

We have compared the effectiveness of RSC, SRSC, vermiculite, and soil against root proliferation of “M.9” apple rootstock. Although SRSC did not cause early root initiation, the final root numbers and fresh and dry weight of roots treated with it were the greatest among the materials. It was suggested that SRSC was the most suitable material for “M.9” apple root propagation by mound layering, but as SRSC needs watering twice a day R + S could be used alternately. As the weights of RSC and SRSC are far lighter than that of soil, these materials should be used instead of soil for the reduction of labor.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

The authors are indebted to Dr. T. Tsuge for supplying the rice seed coat. They also wish to thank Dr. R. Nakajima for his technical assistance. This research was carried out under the Project for the Promotion and Enhancement of the Afghan Capacity for Effective Development (PEACE).

Root Stock

The term rootstock originates from the world of grape growing, in which the rootstock of one vine would be paired with another grape varietal to overcome specific conditions that would otherwise prevent that varietal from being grown in that specific area.

Of course, grapes are only one example of rootstock and grafting. The process can be used with any number of plants, including annuals, perennials, trees, and more. It has become particularly popular with fruit tree growers, but is also practiced by gardeners striving to maximize their per-foot garden yield.

Rootstock is chosen for any number of reasons. One might be the age and development of the stock in question. For instance, an old, established grape vine has very deep roots that supply the entire vine with adequate moisture even in dry years when young vines would die. Grafting another vine onto existing rootstock in this situation would allow a younger vine to thrive.

Rootstock can be chosen for its resistance to pests and diseases, as well. For instance, one variety of grape vine might be resistant to particular types of fungi, mold or nematodes in a specific geographic area, but the grower might prefer a different grape varietal. Grafting allows the desired varietal to be grown in that area without worrying about susceptibility to pests or diseases.

Rootstock Information – Why Do We Use Rootstock For Trees

When you have children, providing a good variety of healthy snacks is always a challenge, especially when the price of produce increases all the time. The logical choice for many families is growing their own fruits and vegetables. This seems easy and straightforward enough: plant seeds, grow food, right?

However, once you start reading up on growing fruit trees, you’ll discover many fruit trees planted by seed can take three to eight years to start producing fruit. In eight years, the kids may be off to college or starting families of their own. For this reason, many gardeners choose to purchase immediately fruiting trees that are grafted on already established rootstock. What is rootstock? Continue reading to learn about rootstock plants.

Rootstock Information

Rootstock is the base and root portion of grafted plants. A scion, the flowering and/or fruiting part of the plant, is grafted onto rootstock for a variety of reasons. The scion and rootstock must be of closely related plant species in order for the graft to work. For example, in fruit trees, pitted fruit like cherry and plum can be rootstock and scion for each other, but an apple tree cannot be used as rootstock for a plum scion and vice versa.

Rootstock plants are selected not only for their close relation to the desired plant, but also for the attributes it will give to the desired plant. In the world of grafting, there are many more scion varieties available than rootstock varieties. Rootstock varieties may come from naturally growing trees, unique naturally occurring plant mutations or be genetically bred for the purpose of being rootstock.

When a successful rootstock plant is identified, it is then propagated asexually to create exact clones of it for use as future rootstock.

Why Do We Use Rootstock for Trees?

Grafting onto rootstock that is already established allows young fruit trees to bear fruit earlier. Rootstock plants also determine the tree and root system size, fruit yield efficiency, longevity of the plant, resistance to pests and disease, cold hardiness and the tree’s ability to adapt to soil types.

Common types of fruit are grafted to dwarf fruit tree rootstock to create dwarf or semi-dwarf varieties which are easier for homeowners to grow in small plots, and also allow orchard growers to grow more trees per acre, therefore, producing more fruit per acre.

Some cold tender fruit tree varieties are also made into varieties that can withstand more cold by grafting them on to hardier rootstock. Another benefit of grafting onto rootstock is that fruit trees that require a pollinator can actually be grafted onto the same rootstock as their required pollinator.

While the importance of rootstock plants is mostly stressed in fruit crops, other plants are grafted onto rootstock to create specialty or ornamental trees. For example, a knockout rose shrub in tree form is not a naturally occurring tree or the result of pruning and training. It is created by grafting a shrub onto related rootstock. Even common trees such as maples are grafted onto specific maple rootstock plants to make better quality maple trees.

Rootstocks explained

by Nik Magnus | © 2009 | www.woodbridgefruittrees.com.au

Rootstock before grafting

A rootstock is an simply a variety selected especially for it’s disease resistance, health and vigour. These characteristics are passed onto the whole tree once the desired variety is grafted on top.Rootstocks are usually grown in stool beds where they are layered down and the vertical shoots harvested along with a few roots at their base. Because they are propagated this way, they are genetically identical to each other and the result entirely predictable. They themselves don’t produce fruit of any quality, but when grafted with a good scion wood (a piece cut from another tree of a known variety) it acts as a supporting stem and root system for that variety to grow. The final tree size is influenced by the dwarfing nature of the rootstock and the vigour of each individual variety.

Anatomy of a graftling

Modern apple growers have the East Malling Research Station to thank for the rootstocks we use today. Bred primarily to increase the resistance to woolly aphid (see seperate article) it produced a spectrum of extra dwarfing, dwarfing and semi dwarfing rootstocks. The common apple rootstocks known today include M9, M27, M26, MM106 and MM111.

Other fruit trees have their dedicated rootstocks.

By grafting the scion onto the rootstock, we keep the variety identical to the parent tree, but allow the properties of the rootstock to come through – like growth habit, disease resistance and water requirement / drought tolerance.

Rootstock size chart

Cooperative Extension: Tree Fruits

Rootstocks and Dwarf Fruit Trees

Full-sized (top) and semi-dwarf (lower) Cortland apple trees.

Fruit trees vary in how large they become when fully grown. Apples, pears, and cherries can range in size from large standard types to dwarf types that are not much bigger than shrubs. Since they remain small even when fully grown, dwarf fruit trees are an option for small yards, or where many different varieties will be planted in a small area. Dwarf types are widely available for most varieties of apple and sweet cherry, but not for pear. Dwarf types do not yet exist for peach, plum or apricot.

The dwarfing trait does not occur in the variety, but in the rootstock to which it is grafted. This means that popular varieties such as Northern Spy can be grown as a dwarf or as a full sized apple tree depending on the type of rootstock.

Fruit trees are grafted to rootstocks rather than being grown from seed. This is because they are not “true-to-type” when grown from seed. Seeds from a McIntosh tree will not grow into another McIntosh tree, but will be a unique variety. This is true of seeds from other fruit trees, as well. In order to propagate trees of a particular variety, one must start with cuttings or buds of that same variety. The McIntosh variety originated over 200 years ago from tree that was grown from a seed. Since then, all other McIntosh trees have been derived from that original tree.

Rootstocks serve as the root system of the tree. Prior to grafting, they start out as complete trees with a root system and a single stem. Bud grafting is usually done in summer when leaf buds on new shoots can be sliced off the stem and inserted under the bark of the rootstock. The grafted bud joins to the rootstock over the next several weeks. After the graft heals, the rootstock is pruned at a point just above the bud. The following spring, the grafted bud will sprout and grow into a new shoot that eventually becomes the fruit-bearing portion of the tree.

There are many different varieties of apple and cherry rootstocks, and they vary in how much dwarfing they induce in the grafted variety. Some are highly dwarfing whereas, some are semi-dwarfing.

In addition to tree size, apple rootstocks affect the age at which they begin to bear fruit. In general, dwarf fruit trees begin to bear two to three years after planting. Semi-dwarf apple trees and most pear trees begin to bear fruit four to five years after planting. Standard apple trees can take as much as seven to ten years to reach an age when they bear fruit. Regardless of the rootstock, peach, plum and cherry trees begin to bear fruit at an age of three to four years.

Dwarf apple and pear trees have weak roots and will not support themselves once they bear fruit. They should be held upright with a stake or trellis so that the roots do not break and for the tree to remain upright. Semi-dwarf trees do not need staking.

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