Determination of optimal plant growth regulators for breaking seed dormancy and micropropagation of Sorbus aucuparia L.

Sorbus aucuparia L. is an important forest tree used in the reforestation of high-altitude mountainous areas, which carries significant pharmaceutical, industrial, ornamental, food, and ecological properties. However, the seed propagation and micropropagation of mature trees of S. aucuparia L., presents various difficulties which are integral aspects for the re-propagation and breeding of novel cultivars. In this study, we isolated the mature embryo-containing seeds of selected varieties of S. aucuparia L. from their seed coat and used them directly as explants in vitro to investigate and determine the optimal dose of cytokinin in breaking seed dormancy and micropropagation. 3 mg/L of benzyl adenine (BA) in addition to different concentrations and combinations of kinetin (0.5, 1, and 2 mg/L), indole-3-butyric acid (IBA) (0, 1, 0.5, and 1 mg/L), and 1-naphthalene acetic acid (NAA) (0, 1, 0.5, and 1 mg/L) were applied within a Murashige and Skoog (1962) (MS) medium at germination inhibition, shoot elongation, and shoot proliferation. In the MS mediums containing BA and kinetin, germination was achieved at the end of 1 week, and shoot proliferation was achieved at the end of 3 weeks. The most successful germination (96%), tallest shoot length (mean 5.1 cm), most shoot proliferation (mean 7.2 pieces), and number of nodes (mean 9.7 pieces) were identified in the MS containing 3 mg/L BA and 1 mg/L kinetin. Direct root formation with shoot elongation occurred in 25% of explants which germinated in the MS medium. For shoots propagated without roots in this medium, 62% of these achieved rooting at the highest dose of 1 mg/L indole-3-acetic acid (IAA) using a two-stage rooting method. Rooted shoots were successfully transferred to an ex vitro medium. These results provide a basis for breaking seed dormancy of selected Sorbus L. genotypes quicker, leading to more effective clonal production. Keywords: Sorbus aucuparia L., rowanberry, tissue culture, seed dormancy, micropropagation, in vitro