Use of Interstocks and Interstems Interstock or interstem trees are comprised

Cheryl R. Hampson 1 and Henk Kemp 2

5.11 Use of Interstocks and Interstems Interstock or interstem trees are comprised

of three genetically different components (Fig. 5.6).

Traditionally, interstocks (interstems) were used in raising fruit trees only when

graft compatibility between the rootstock and scion was a problem. This is a common practice when raising certain cultivars of pear on quince rootstocks. Interstock use in apple is less widespread and is generally only applicable when either the desired dwarfing rootstock is difficult to propagate on its own roots (e.g. Ottawa 3) or the soils are unsuited to planting dwarfing rootstocks (e.g. infested with woolly apple aphid or subject to drought or waterlogging). Trunk builders or ‘staddles’ of winter-hardy culti-vars, such as ‘Hibernal’, have been used for a very long time in central Europe to prevent freeze damage to the tree trunk, and cold-tolerance benefits have also been recorded when using interstems of more usual length (Wertheim, 1985).

It is fortunate that, for reasons not understood, a significant part of the dwarf-ing influence of an apple rootstock is attrib-utable to factors associated with its shank (stem piece) rather than its root system.

This means that, by inserting a short length of the dwarfing rootstock as an interstock between a more invigorating rootstock and the scion, the grower can achieve semi-dwarfed trees. Up to approximately 35 cm in length, the longer the interstock stem piece, the more dwarfing the effect (Parry and Rogers, 1972). Trials in Poland have shown increased productivity when using P.2 as an interstock (Kruczynska and Czynczyk, 1998).

Trees raised with interstocks are slightly more expensive to produce but often their

Graft union

Scion

Interstock or interstem

Rootstock

Fig. 5.6. Dwarfing interstock/interstem in relation to apple scion and rootstock.

benefits warrant this extra expenditure by the grower. Further information on raising trees with interstocks (interstems) can be found in Chapter 6.

Occasionally, stem pieces of other scion cultivars (such as ‘Golden Delicious’ or

‘Summerred’) are inserted between the root-stock and the chosen scion. This can improve

the precocity of cropping and winter-hardiness of the tree. Interstocks can also help regulate the vigour of shoot growth on the scions (Wertheim and Callesen, 2001).

Also, in The Netherlands an interstem of

‘Dubbele Zoete Aagt’ is used with the scion cultivar ‘Cox’s Orange Pippin’ to prevent trunk rot caused by P. cactorum.

Further General Reading on Apple Rootstocks

Ferree, D.C. and Carlson, R.F. (1987) Apple rootstocks. In: Rom, R.C. and Carlson, R.F. (eds) Rootstocks for Fruit Crops. Wiley Interscience, New York, pp. 107–144.

Hatton, R.G. (1917) Paradise apple rootstocks. Journal of the Royal Horticultural Society 42, 361–399.

Lockhard, R.G. and Schneider, G.W. (1981) Stock and scion growth relationships and the dwarfing mech-anisms of apple. Horticultural Reviews 3, 315–375.

Sadowski, A. and Hrotko, K. (1999) Apple Rootstocks for Intensive Orchards. Proceedings of an International Seminar, Warsaw, 18–21 August 1999. Department of Pomology, Warsaw Agricultural University, Poland, and Department of Pomology, University of Horticulture and Food Industry, Budapest, Hungary, 131 pp.

Tubbs, F.R. (1972) Research fields in the interaction of rootstocks and scions in woody perennials, Parts 1 and 2. HortAbstracts 43, 247–253, 325–335.

Webster, A.D. (1995) Temperate fruit tree rootstock propagation. New Zealand Journal of Crop and Horticultural Science 23, 355–372.

Wertheim, S.J. (1998) Apple rootstocks. In: Rootstock Guide: Apple, Pear, Cherry, European Plum. Fruit Research Station, Wilhelminadorp, The Netherlands, pp. 19–59.

References

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Parry, M.S. and Rogers, W.S. (1972) Effects of interstock length and vigour on the field performance of Cox’s Orange Pippin apples. Journal of Horticultural Science 47, 97–105.

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Perry, R.L. (1990) Mark in the rootstock arsenal. Compact Fruit Tree 23, 1–3.

Perry, R.L. (1992) The relative susceptibility of rootstocks to fire blight. Proceedings of the Michigan State Horticultural Society 122, 72–75.

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S.J. Wertheim

and Anthony D. Webster

1Fruit Research Station, Randwijk, The Netherlands; ²Crop Science Department, Horticulture Research International, East Malling, West Malling, Kent, UK

6.1 Introduction 126

6.2 Seed Propagation 126

6.3 Vegetative or Clonal Propagation 127

6.3.1 Stooling 128

6.3.2 Layering 129

6.3.3 Cuttings 131

6.4 Micropropagation 135

6.4.1 Propagation in vitro 135

6.4.2 Practical applicability 136

6.5 Tree Raising 136

6.5.1 Site choice 136

6.5.2 Planting distance 137

6.5.3 Rootstock cutting (heading) back and bleeding 137

6.5.4 Plant material 138

6.5.5 Tree support 139

6.5.6 Trunk cleaning 139

6.5.7 Other types of plant material 140

6.6 Budding and Grafting 140

6.6.1 Bud wood 141

6.6.2 Rootstocks, budding height and site 141

6.6.3 Budding and grafting methods 141

6.6.4 Tying and after care 142

6.6.5 Bench grafting 143

6.7 Branching 143

6.7.1 Manipulation of branching by hand 143

6.7.2 Manipulation of branching by chemicals 144

6.8 Defoliation and Digging Up (Lifting) Trees 146

(eds D.C. Ferree and I.J. Warrington) 125

6.1 Introduction

In nature, apple trees multiply by seeds, but when apple trees are grown commercially or by the home gardener the common propaga-tion method is to bud or graft scion cultivars on to selected rootstocks. The reason for propagation by means of rootstocks is that apple cultivars are not true to type when propagated by seed and, at least in former days, difficult, if not impossible, to propagate by vegetative means. Thus, when a seedling with good fruiting characteristics was found, it could not be multiplied by sowing its seeds or by use of layering or cutting techniques.

Today, vegetative propagation techniques have improved so much that scion cultivars can be multiplied by cuttings or by micro-propagation in the laboratory. Nevertheless, the use of rootstocks has remained dominant, because most of the currently grown scion cultivars, once self-rooted, do not perform well in the orchard. Scion trees propagated

‘on their own roots’ are more vigorous, come later into bearing and crop less efficiently than those on good rootstocks.

Apple seedlings must have been the first rootstocks used extensively by early horticul-turists, largely because seeds were readily available. Only after it was observed that some apple cultivars could be easily propa-gated by layering did vegetative or clonal

In document Apples - Botany, Production and Uses (Page 132-139)