The Effect of 6-Benzylaminopurine (BAP) on Bud-forcing of Twelve Quercus L. Species

Oaks (Quercus L.) are globally iconic trees, prized economically for their strong, rot-resistant wood, ecologically for their contributions as a keystone species, and aesthetically for their ornamental landscape value. One method of propagating oak species is micropropagation using young, newly flushed shoots collected immediately after emergence in the spring.  This is a narrow and somewhat unpredictable time window for obtaining explants.  However, forcing bud break of cuttings can increase the time range to collect young shoot explants and allow for shoot development in a controlled, clean environment.  The objective of this experiment was to determine the effectiveness of 6-benzylaminopurine (BAP), a cytokinin, on bud break in twelve Quercus species.  Dormant cuttings of one- and two-year-old wood were collected from 12 different species of Quercus: alba, bicolor, cerris, falcata, imbricaria, macrocarpa, macrocarpa var. macrocarpa, pagoda, palustris, rubra, texana, and variabalis.  Cuttings of 10-33 cm in length with 5-25 buds each (depending on species) were collected in Kennett Square, Pennsylvania, in mid-February.  The experiment was a factorial design with 12 species, 3 BAP treatments (0, 100, and 500 ppm) and 3 replications, giving a total of 108 cuttings.  Each of the 3 repetitions were placed into Erlenmeyer flasks with distilled water and placed in a greenhouse with a heat set point of 20°C and a cooling set point of 26.5°C.  Cuttings were evaluated weekly and rated on a scale of 0-4 with 0 = no development, 1 = slight bud swelling, 2 = moderate bud swelling and elongation with visible green coloration, 3 = bud break with partially visible leaf and inflorescence tips, 4 = newly emerged leaf fully visible (target stage for shoot tip micropropagation).  Results indicate that the BAP treatment at 100 or 500 ppm significantly increased the rate of bud break and shoot elongation by 1-2 weeks for four of the Quercus species: imbricaria, macrocarpa, pagoda, and variabilis.  There was no significant effect from BAP application on the remaining eight species.  All Quercus species except alba, bicolor, and pagoda reached stage 4 with all treatments indicating that forcing bud break without BAP application is a viable option, but the rate may be enhanced with some species with the application of BAP.