Phenotypic Variation of Advanced Dichroa x Hydrangea Hybrids

Hydrangea macrophylla is the most popular Hydrangea species sold in the United States with sales of over $32 million annually in the horticulture and floriculture industries.  Addition of aluminum to soilless media is required to produce highly desirable blue flowers at the point of sale, which represents increased labor costs and may lower the pH to toxic levels in the plant container.  Dichroa febrifuga, a member of the Hydrangaceae, produces blue flowers in the absence of aluminum and blue fruits that persist throughout winter.  The goal of the current project is to produce and evaluate interspecific hybrids that combine the desirable traits of blue fruits, stable blue flower color, larger flowers, and evergreen foliage found in D. febrifuga with cold-hardiness and the showy flowers with large sepals found in H. macrophylla.  The F1 hybrid Dichroa x H. macrophylla ‘Taube’ was selected as a female parent for advanced generation hybridization due to its large flowers, compact form, and low disease incidence.  Of all backcrosses to an H. macrophylla parent, the BC1 [(Dichroa x ‘Taube’) x Souvenir du President Doumir] had the highest percentage of pollinations producing fruit with seeds and the highest number of surviving seedlings per fruit.  A total of 32 [(Dichroa x ‘Taube’) x Souvenir du President Doumir] BC1s were generated.  All contain the dark, evergreen leaves of Dichroa and the showy sepals of the H. macrophylla male parent.  Evaluation for height, form, flower color, flower size, and number of flowers is ongoing.   We expect these hybrids to constitute an important source of germplasm for Hydrangea improvement.