Blackberry traditionally has been propagated using vegetative methods including tip layering, cane cuttings (soft and hard), root cuttings, and tissue culture (TC) (Caldwell, 1984). Large commercial blackberry nurseries use TC techniques that are expensive and need a high capital investment, but a few small nurseries are still using leafy softwood cuttings taken in summer from stock plants growing in screen house to propagate blackberry plants (J. Ballington, personal communication). Propagation of some erect-type blackberries by softwood cuttings and root pieces appear feasible (Busby and Himelrick, 1999; Thompson et al., 2004; Zimmerman et al., 1980). Propagation of blackberry by hardwood or floricane stem cuttings has been reported, but the results have been poor and variable (<50% rooting) (Bray et al., 2003; Lopez-Medina and Moore, 1997; Zimmerman et al., 1980). Treatment of blackberry cuttings with indolebutyric acid (IBA) has given mixed results (Busby and Himelrick, 1999; Zimmerman et al., 1980). Rooting in hardwood cuttings occurred at the base of the cuttings, but the cause of poor rooting in some cultivars was attributed to overwatering (Zimmerman et al., 1980). Each of the traditional non-TC methods has its disadvantages. Tip-layering technique is laborious and the ratio of new transplants produced per stock plant is usually low (Hartmann et al., 1997). To root leafy, softwood material, the cuttings must be stuck in root media and misted intermittently for several weeks. For commercial acceptance of a propagation method, stock plants must produce plant material in large numbers, and the collection and handling of propagation material must be cost effective. A simple, inexpensive method that will generate high numbers of rooted cuttings is preferred.
Rooting leafy cuttings of ornamental crops with one to several nodes can be done in enclosed systems (Hartmann et al., 1997), in which watered-in cuttings are placed in plastic tents without intermittent misting using the following environmental conditions: rooting media temperature of 18 to 25 °C, atmosphere that is conducive to low water loss, and light level that is not excessive. Rooting of hardwood cuttings under a plastic tent without mist was reported to be as good as rooting under intermittent mist in some thornless blackberry (Zimmerman et al., 1980). In a preliminary study, several adventitious roots developed at the base of most axillary buds on five-node hardwood cuttings of ‘Siskiyou’ with their base submersed in water and stored in sealed plastic bags (F. Takeda, personal observation).
Flower bud initiation in blackberry occurs in the fall. Floral primordia in trailing blackberry (e.g., ‘Siskiyou’) differentiate in the fall, but floral primordia in eastern thornless blackberry (e.g., ‘Triple Crown’) are not visible until spring (Takeda et al., 2002; Takeda and Wisniewski, 1989). The presence of an actively growing shoot tip is necessary during the first 3 or 4 d after the cuttings are made for root formation to occur (Hartmann et al., 1997), but if the apical meristem that is already reproductive is left intact on hardwood blackberry cuttings, the shoots that emerge during propagation likely will end in flowers. Excising the distal half to two-third of the axillary bud should remove the differentiated meristem. Cytokinin application to buds favors shoot formation and inhibits root initiation in stem cuttings, but in decapitated pea (Pisum sativum) cuttings, cytokinins at very low concentrations promoted root initiation (Erickson, 1974; Heide, 1965).
One objective of this study was to assess whether one-node and two-node hardwood cuttings of ‘Siskiyou’ and ‘Triple Crown’ could be rooted in an enclosure system. A second objective was to determine the effects of cytokinin application and bud removal on adventitious root and shoot (flowering and vegetative) development in hardwood cuttings collected in winter.
Bray, M.M., Rom, C.R. & Clark, J.R. 2003 Propagation of thornless Arkansas blackberries by hardwood cuttings Discovery (Univ. of Arkansas) 4 9 13
Busby, A.L. & Himelrick, D.G. 1999 Propagation of blackberries (Rubus spp.) by stem cuttings using various IBA formulations Acta Hort. 505 327 332
Erickson, E.N. 1974 Root formation in pea cuttings. III. The influence of cytokinin at different development stages Physiol. Plant. 30 163 167
Hartmann, H.T., Kester, D.E., Davies F.T. Jr & Geneve, R.L. 1997 Plant propagation: Principles and practices 6th ed Prentice Hall Upper Saddle River, NJ
Heide, O.M. 1965 Interaction of temperature, auxin, and kinins in the regeneration ability of Begonia leaf cuttings Physiol. Plant. 18 891 920
Takeda, F., Hummell, A.K. & Peterson, D.L. 2003 Effects of cane number on yield components in ‘Chester Thornless’ blackberry on the rotatable cross-arm trellis HortScience 38 377 380
Takeda, F. & Wisniewski, M. 1989 Organogenesis and patterns of floral bud development in two eastern thornless blackberry cultivars J. Amer. Soc. Hort. Sci. 114 528 531
Takeda, F., Strik, B.C., Peacock, D. & Clark, J.R. 2002 Cultivar differences and the effect of winter temperature on flower bud development in blackberry J. Amer. Soc. Hort. Sci. 127 495 501
Thompson, E., Clark, J.R. & Rom, C.R. 2004 Propagation of thornless blackberries utilizing adventitious shoots from root cuttings. Discovery (Univ. of Arkansas) 5 93 97
Washington State Department of Agriculture 2010 Title 16, Chapter 16–333, Washington Administrative Code, Certification of caneberry planting stock 14 Jan. 2011 <http://apps.leg.wa.gov/WAC/default.aspx?cite=16-333>.
Zimmerman, R.H., Galletta, G.J. & Broome, O.C. 1980 Propagation of thornless blackberries by one-node cuttings J. Amer. Soc. Hort. Sci. 105 405 407