Production and verification of Hydrangea arborescens 'Dardom' x H. involucrata hybrids

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.) 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 reciprocal 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' x 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.