Development of Novel Breeding Stock in Buddleja davidii through Mutation Breeding and Haploid Induction

Buddleja davidii Franch. is a popular perennial shrub originally from China. Its flowers attract butterflies, hence its common name butterfly bush. While a number of cultivars already exist, from a plant breeder\u27s perspective, there are still several traits which could be improved upon. Smaller plant size, improved plant architecture, increased flower color range and most importantly, the creation of sterile selections, could lead to novel varieties worthy of introduction. Sterility is an important consideration because the species is classified as a noxious or invasive weed in several regions of the United States, and the state of Oregon has recently implemented a ban on the species and all of its cultivars. Through chemical mutagenesis we identified a dwarf mutation that is inheritable as a single dominant allele. The principle difference in the mutation is reduced internode length. Outcrosses to several standard cultivars to examine the heritability of the mutation have lead to some interesting materials that could support a continued breeding effort. A new\u27 variegated selection was also identified as part of the original mutant screen. External trials have been implemented with the desire to patent this new variegated buddleja and introduce it for production. Also, we have attempted to create potentially sterile triploid cultivars of the species through haploid induction. By means of irradiated pollinations we created di-haploid (2n) plants with the intent of breeding these to tetraploid cultivars. Unfortunately, these di-haploid plants proved to be sterile and are not useful for the creation of triploid progeny. A final component of our work was to develop a testing protocol to evaluate seed production potential, a key factor in this species invasiveness, for use in applying for an exemption from an invasive species ban for a specific cultivar.