Submitted to: HortScience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/1/2005
Publication Date: 1/6/2006
Citation: Jones, K.D. and Reed, S.M. 2006. Production and verification of Hydrangea arborescens 'Dardom' x H. involucrata hybrids. HortScience. 41:564-566. Interpretive Summary: Hydrangea paniculata and H. arborescens are the most cold-hardy Hydrangea species. Hydrangea paniculata, which is commonly known as panicle hydrangea, produces white flowers that sometimes age to pale pink. Hydrangea arborescens, or smooth hydrangea, has pure white flowers that age to pale green. Previous attempts have been made to combine flower color and cold hardiness in Hydrangea by hybridizing these two species to bigleaf hydrangea (H. macrophylla), which has deep blue to pink flowers. Hybrids were produced but were weak and infertile. The purpose of this study was to determine if H. involucrata could be used as an alternative to H. macrophylla as a source of flower color in Hydrangea interspecific hybridizations. Hydrangea involucrata is a medium-sized shrub that produces large lavender-blue lacecap flower heads in mid-summer. Its large velvety leaves add to its ornamental value. Controlled pollinations were made between H. involucata and the cold hardy species H. paniculata and H. arborescens. Seven hybrids between H. arborescens ‘Dardom’ (White Dome) and H. involucrata were obtained. These plants were verified as hybrids using molecular markers, chromosome counts and morphological comparisons of offspring and parents. As hybrids flower, they will be hybridized to each other and to their parents in an effort to obtain plants with the desired combination of flower color and cold hardiness.
Technical Abstract: Previous attempts to use interspecific hybridization to combine flower color and cold hardiness in Hydrangea have not produced the desired results, with confirmed hybrids being weak, sterile or aneuploid. In all cases, H. macrophylla Thumb. Ex J.A. Murr. (Ser) was used as the source of flower color. This work investigates the use of H. involucrata Sieb. as an alternative source of flower color in Hydrangea interspecific hybridizations. Controlled pollinations of H. involucrata with two cultivars of H. arborescens L. and three cultivars of H. paniculata Sieb. were made. Hybridity of progeny was verified using RAPD markers and confirmed with chromosome counts and morphological comparisons of hybrids and parents. Plants were obtained only when H. involucrata was used as the pollen parent. No hybrids between H. paniculata or H. arborescens ‘Annabelle’ and H. involucrata were produced. Seven H. arborescens ‘Dardom’ x H. involucrata progeny showed either a sum of the RAPD bands of both parents or banding patterns that matched those of H. involucrata. Leaf blade length and length/width ratio of the hybrid were intermediate to its parents. Chromosome number in the hybrid (2n = 34) was also intermediate between H. arborecens (2n = 38) and H. involucrata (2n = 30). One ‘Dardom’ × H. involucrata plant flowered in 2005. While pollen staining indicated a very low level of fertility, we will continue to evaluate the possibility of using the hybrid for producing advanced filial or backcross progeny.