Optimization of In Vitro Regeneration of Pinus peuce (Gris.)

Pinus peuce (Macedonian pine) is considered a valuable ornamental tree that is frequently planted in parks and gardens, especially in Western Europe. This endemic pine is one of the most valuable conifer species in its native range, which currently consists of only two disjunct populations restricted to small mountainous areas of the Balkans and is listed as a near-threatened species. The reproduction of Macedonian pine by seed is limited, so in vitro propagation methods have emerged as a promising tool for large-scale propagation. The objective of this study was to develop an improved system for the micropropagation of P. peuce from juvenile plant material using a short-term liquid cytokinin pulse. For that, explants derived from 4-week-old seedlings were pulse-treated with different concentrations of N-6-benzyladenine (BA) for 1 or 2 h to stimulate the induction of axillary buds. The highest axillary shoot formation was achieved with 222 mu M BA pulse treatment, with an average number of similar to six shoots per explant. Elongated shoots (>= 10 mm) were detached from the explants and pulse-treated with 0.27 or 1.08 mM alpha-naphthaleneacetic acid (NAA) or 0.25 or 0.98 mM indole-3-butyric acid (IBA) for 1 or 2 h. IBA was more effective than NAA and led to a maximum rooting percentage (up to 40%) and the highest number of acclimatized plants (15-20%). Rooted plants were successfully transferred to ex vitro conditions.