Bud-forcing and in vitro culture for conservation of oak (Quercus L.)
Date
2016
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Publisher
University of Delaware
Abstract
Oaks (Quercus L.) are globally iconic trees, prized for their contributions as a keystone species, strong, rot-resistant wood, and landscape value. Despite their importance, many species of Quercus are under threat from a range of issues, such as habitat loss and attacks from pests and diseases. Conservation efforts for this genus can be complex and challenging, especially since Quercus species are considered “recalcitrant” due to the inability of their seeds, acorns, to survive seed banking, an important conservation method. One method to support conservation efforts is in vitro culture (tissue culture) using newly-flushed shoot tips. Two experiments were conducted to determine 1) the viability of bud-forcing Quercus and effectiveness of 6-benzylaminopurine (BAP), a cytokinin, on stimulating bud break and shoot elongation of Quercus and 2) the responses of species from the three North American Quercus sections (Lobatae, Quercus, and Protobalanus) on two different media in in vitro culture.
Natural shoot emergence in the spring is a narrow and somewhat unpredictable time window, but forcing bud break of cuttings can lengthen this window in a controlled environment. Experiment 1 involved dormant cuttings collected from 12 Quercus species placed into flasks of distilled water. Flasks were placed in a greenhouse with weekly BAP treatments applied by paint brush at either 0, 100, or 500 ppm. Results varied by species. The BAP treatment at 100 or 500 ppm significantly increased the rate of bud break and shoot elongation for four of the Quercus species ( imbricaria, macrocarpa, pagoda, and variabilis) and significantly decreased the rate of bud break and shoot elongation in Q. falcata. There was no significant effect from BAP application on the remaining seven species. A majority of the Quercus species reached the target stage for micropropagation with all treatments, indicating that forcing bud break is a viable option for Quercus, but the rate of bud development in some species may be enhanced by BAP application.
In Experiment 2, newly-flushed shoots were collected in the spring from 12 species of Quercus representing the three North American Quercus sections (Lobatae, Quercus, and Protobalanus) (different species from Experiment 1). The shoot explants were grown in vitro on one of two media formulations: Gresshoff and Doy (GD) basal salts and vitamins or Lloyd and McCown Woody Plant (WP) basal salts with Murashige and Skoog (MS) vitamins. Responses of growth, survival, and contamination varied by species, but these differences were concealed when grouped by section. Growth responses of leaf expansion, bud expansion, shoot production, and callus production were observed in nine of the species. Explants grown on WP/MS media had significantly more growth responses and longer survival times than those on GD media.