2017 ASHS Annual Conference

Hydrangea paniculata is a valuable and popular landscape shrub in temperate parts of the world. To better understand their reproductive biology, diverse cultivars, interploid hybrids, and wild-collected accessions of H. paniculata were analyzed for ploidy levels and relative genome sizes by flow cytometry and cytology. Most cultivated varieties were found to be tetraploid, though hexaploid and pentaploid clones were identified. Crosses between pentaploids and tetraploids tended to produce progeny with genome sizes within or near the tetraploid range, suggestion a bias towards euploidy/isoploidy. Open-pollinated pentaploids produced progeny with genome sizes ranging from near tetraploid to near pentaploid, as well as one plant greater than heptaploid, most likely resulting from an unreduced gamete from one parent. Although diploid H. paniculata have been documented in Japan, is appears that tetraploids and to a lesser degree hexaploids have been preferentially selected for horticultural use. These results document genome sizes and ploidy levels of diverse cultivars, hybrids, and wild-collected accessions of H. paniculata. Furthermore, it was found that interploid hybrids can be easily produced and that pentaploid hybrids maintain fertility and can produce offspring with a wide range of cytotypes including aneuploids, (near) euploids, and higher ploidy levels resulting from unreduced gametes.