2017 ASHS Annual Conference

Maples are common shade and street trees that make up a substantial percentage of the urban canopy and are of great economic importance to the nursery industry. Unfortunately, some species have escaped cultivation and become established in native forests. Specifically, Acer platanoides (Norway maple) and A. ginnala (=A. tataricum ssp. ginnala; Amur maple) are listed as noxious weeds in Connecticut and the former is listed in Massachusetts. Amur maple has naturalized from Kentucky north through the Canadian provinces of Saskatchewan, Manitoba, and Ontario. Norway maple has naturalized over an even greater area including an area similar to Amur maple in the eastern US as well as the western US from Oregon and Idaho north to British Columbia. Less fecund cultivars would benefit growers by allowing them to maintain these species in their product line but also prevent further spread from cultivation and any potential negative ecological impacts. We developed tetraploids (4x) of Norway and Amur maples in 2011 and 2012, respectively. Early attempts for controlled crosses were largely unsuccessful for Amur maple in 2014, therefore all plants were field-planted in fall 2014. Tetraploids were interplanted with diploids (2x) and allowed to open-pollinate. In 2016, 471 seeds were collected from one tetraploid Norway maple and 3,574 seeds were collected from five Amur maple tetraploids including two cytochimeras that were confirmed to have tetraploid LII histogenic layers. Seed germination varied among parents but was approximately 10% for both Amur (372 seedlings) and Norway (46 seedlings) maples. Preliminary ploidy analysis revealed intraspecific variation in the percentage of triploid (3x), tetraploid (4x), and pentaploid (5x) plants derived from each parent. For example, one Amur maple parent (OSU74.19) produced 0% 3x, 12.5% 4x, and 87.5% 5x, whereas OSU74.22 produced 100% 3x. Overall, seedlings derived from Amur maple tetraploids were 74% 3x, 14% 4x, and 12% 5x. The single Norway maple produced similar percentages with 66.7% 3x, 16.7% 4x, and 16.7% 5x. Factors that may have affected the ploidy levels of progeny include relative rates of self-pollination, unreduced gametes, sex expression (percentage of staminate vs. perfect flowers), and field position relative to diploids. Future investigations will assess rates of self-pollination, rates of unreduced gametes, and fertility of progeny with various ploidy levels.