Interspecific hybridisation within Buxus spp.

•The first study to explore the possibilities of interspecific hybridisation in Buxus.•Within Buxus, no prezygotic barriers exist.•Postzygotic barriers occur, e.g. lack of seed germination or unilateral incongruity.•Existing ploidy differences in Buxus do not create a bottleneck for obtaining F1 hybrids.•Hybrid status of F1 seedlings is confirmed by flow cytometry or AFLP analysis.

Breeding efforts within Buxus have been limited, despite the great morphological and genetic variation within this genus. To evaluate the possibilities for creating novel cultivars through interspecific hybridisation within Buxus, we have made over 7500 interspecific crosses involving Buxus harlandii Hance, Buxus sempervirens L., Buxus microphylla Sieb & Zucc, Buxus balearica Lam., Buxus colchica Pojark and Buxus henryi Mayr. Germination of the resulting interspecific seeds was between 0% and 47% for some cross combinations. In total 4750 interspecific F1 seedlings were obtained. The hybrid nature of most seedlings could be proven using AFLP markers or flow cytometry. As expected, crosses at diploid level or tetraploid level were efficient. Moreover, our results showed that interploidy crosses (diploid × tetraploid) were also efficient.This study is the first in-depth exploration of the possibilities of interspecific hybridisation within Buxus. These results may become a valuable tool to create new Buxus cultivars with desirable traits.