Induced Autotetraploidy Results in Reduced Fertility in ‘Crimson Pygmy' Japanese Barberry

 Japanese barberry (Berberis thunbergii) is a desirable landscape shrub; however, it is identified as invasive in more than 30 eastern and central U.S. states and Canada. Berberis thunbergii ‘Crimson Pygmy’ is one of the most popular cultivated varieties of Japanese barberry. Diploid (2n) ‘Crimson Pygmy’ were induced to autotetraploidy (4n) in vitro via treatment of nodal explants with the mitotic inhibitor, colchicine. Diploid and tetraploid plants were grown in containers and established in a field containing many other diploid and tetraploid Berberis thunbergii genotypes. Formal evaluations of fruit and seed production were conducted in 2012, 2013 and 2014 when plants were 8, 9, and 10 years old. Based on acetocarmine staining and pollen germination tests, tetraploid plants had similar male fertility to diploid controls. In 2014, tetraploid plants produced 1.3 seeds per plant in comparison to 783 seeds per plants for diploid controls of the same age. Almost all fruits on tetraploid plants contained small, black aborted embryos, and most fruits dropped from plants by my mid-July. Seeds from tetraploid plants exhibited germination percentages that were half those for seeds from diploid plants. Since tetraploid Crimson Pygmy barberries produce only 0.2% of the seed produced by diploid Crimson Pygmy plants, their use in the landscape should present a minimal invasive risk to the environment.