Pecan trees are typically propagated in nurseries using either a whip and tongue graft or a patch bud (Brison, 1974). Seedling pecan trees are sometimes transplanted to their final orchard location where they are grafted 1 or 2 years after transplanting (Smith et al., 2013). Common propagation techniques used in orchards include the two techniques used in nurseries plus the inlay bark graft (Brison, 1974) and the four-flap graft (Stafne and Carroll, 2011). Other propagation techniques can be used, but the four methods listed above are most common. The focus of this article is on grafting success using patch bud propagation.
Grafting success can be divided into three components. First, healthy budwood must be secured that retains viability for propagation. Suitable budwood used for patch budding can be collected while dormant for propagation in the spring or collected during the growing season (Carroll, 2014; Wells, 2014). Dormant wood must be refrigerated and protected from excessive moisture loss. Nesbitt et al. (2002) evaluated moisture conserving packing material, sealing the cut ends of the scion with wax, and storage in polyethylene bags for scion storage 60 to 70 d at 2 °C. They concluded that storing pecan budwood in a polyethylene bag with either no supplemental moisture or slightly moist packing material produced scions with the greatest grafting success. Dormant budwood requires “seasoning” to be used for spring patch budding (Carroll, 2014; Wells, 2014). The bark of the budwood and rootstock must be slipping for successful propagation. Dormant budwood is seasoned by placing it at 80 °F in a polyethylene bag to avoid moisture loss for 4 to 7 d to induce bark slippage.
Patch budding during the middle or latter part of the growing season uses budwood collected the previous day or the same day of use (Brison, 1974; Carroll, 2014; Wells, 2014). Current season’s shoots are recommended for use as budwood. Typically, buds on current season’s growth are immature and unsuitable for patch budding until 10 to 12 weeks after budbreak (Brison, 1974).
The second component of successful propagation is survival of the patch bud. The pecan industry considers a success rate of 75% or greater good (Nesbitt et al., 2002). The preference is for the rootstock and budwood to be about the same diameter; with a 1/2- to 1-inch diameter preferred (Wells, 2014). However, patch budding can be successful when the rootstock budding site is up to 4 inches in diameter. Pecan patch budding success increased with larger rootstocks [60-cm tall and 1-cm diameter to 120-cm tall and 2.5-cm diameter (Maximos et al., 1979)]. Neither girdling (bark removal at the base of the budwood shoot) nor pinching (removing the apical portion of the budwood shoot) the shoot 3 weeks before harvesting for budwood nor the combination of the two affected budding success.
Patch budding is also a commonly used propagation technique for persian walnut (Juglans regia). A study conducted in Greece reported BAP applied at 30 ppm in a lanolin paste to the edge of the rootstock and patch bud before tying with raffia and waxed improved June budding success using dormant collected and then seasoned budwood (Pontikis et al., 1985). September budding using current season or 1-year-old budwood collected during the growing season treated with 30 ppm BAP or 30 ppm gibberellic acid in lanolin improved survival compared with untreated patch buds. Success was similar whether using current season or 1-year-old budwood.
The third component of successful pecan propagation is forcing the patch bud. Typically, the top (i.e., rootstock) is removed above the patch bud, leaving a 4- to 6-inch long stub with the bark stripped to serve as a support stake. As the new shoot grows, it is tied to the stake created by the rootstock. Bud forcing techniques were evaluated for grapefruit (Citrus ×paradise) propagated on sour orange (Citrus ×aurantium) that included bending (bending and tying the top to the base to force the inserted bud at the bend), lopping (cutting partially through the stem 3 to 5 cm above the inserted bud), topping (removal of the top just above the inserted bud), and notching (two parallel cuts 3 to 5 mm apart through the bark above the bud) (Rouse, 1988). Lopping or topping resulted in 97% to 100% of the buds forced after 6 weeks. Bending forced 85% of the buds and resulting shoots were over twice as long as those forced by lopping or topping. Notching only forced ≈40% of the buds.
The objectives of this study were to evaluate selected treatments for pecan propagation by patch budding and methods to successfully force patch buds into growth. Studies addressed 1) budwood age and rootstock age at the budding site, 2) competition from mature trees when budding seedlings during orchard renewal, 3) budwood and rootstock diameter at the budding site, 4) girdling and top removal to force buds, and 5) selected hormone and growth regulator treatments to force buds.
Brison, F.R. 1974 Pecan culture. Texas Pecan Growers Assn., College Station, TX
Carroll, B. 2014 Patch budding pecans. Oklahoma Coop. Ext. Serv. HLA-6206
Littell, R.C., Milliken, G.A., Stroup, W.W. & Wolfinger, R.D. 1996 SAS system for mixed models. SAS Institute, Cary, NC
Luckwill, L.C. 1968 The effect of certain growth regulators on growth and apical dominance of young apple trees J. Hort. Sci. 43 91 101
Maximos, S.E., Rawash, M.A., Dessokey, I., Antoun, N. & Youssef, N. 1979 Studies on the propagation of Curtis pecan by patch budding Egyptian J. Hort. 6 157 167
Nakajima, E., Yamada, K., Kosemura, S., Yamamura, S. & Hasegawa, K. 2001 Effects of the auxin-inhibiting substances rephanusanin and benzoxazolinone on apical dominance of pea seedlings Plant Growth Regulat. 35 11 15
Nesbitt, M.L., Goff, W.D. & Stein, L.A. 2002 Effect of scionwood packing moisture and cut-end sealing on pecan graft success HortTechnology 12 257 260
Pontikis, C.A., Papalexandris, C.X. & Aristeridou, M. 1985 The effect of BA and GA3 on patch budding success of persian walnut seedlings Plant Prop. 31 13 14
Rouse, R.E. 1988 Bud forcing method affects budbreak and scion growth of citrus grown in containers J. Rio Grande Hort. Soc. 41 69 74
Smith, M.W., Goff, W.D. & Wells, M.L. 2013 Pecan orchard renewal: Influence of established trees and remaining stumps on transplant growth and crown gall infection HortScience 48 720 723
Stafne, E. & Carroll, B. 2011 Four-flap grafting of pecans. Oklahoma Coop. Ext. Serv. HLA-6230
Tucker, D.J. 1981 Axillary bud formation in two isogenic lines of tomato showing different degrees of apical dominance Ann. Bot. (Lond.) 48 837 843
Wells, L. 2014 Budding and grafting of pecan. Univ. Georgia Ext. Bul. 1376