Production and Characterization of Intergeneric Hybrids between Dichroa febrifuga and Hydrangea macrophylla

Abstract

The potential of producing an intergeneric hybrid between Dichroa febrifuga Lour. and Hydrangea macrophylla (Thunb.) Ser. was investigated. Reciprocal hybridizations were made between a D. febrifuga selection (GUIZ 48) and diploid (‘Veitchii’) and triploid (‘Kardinal’ and ‘Taube’) cultivars of H. macrophylla. Embryo rescue was employed for about one-third of the crosses that produced fruit, and the rest were allowed to mature on the plant and seed-collected and germinated. Reciprocal hybrids, which were verified with simple sequence repeat markers, were produced from both embryo rescue and seed germination and with both diploid and triploid H. macrophylla cultivars. Hybrids were intermediate in appearance between parents, but variability in leaf, inflorescence, and flower size and flower color existed among the hybrids. A somatic chromosome number of 2n = 6x = 108 was tentatively proposed for D. febrifuga GUIZ 48. Chromosome counts and flow-cytometric measurements of nuclear DNA content indicated that some of the hybrids may be aneuploids, but neither analysis was definitive. Although hybrids with H. macrophylla as the pistillate parent did not form pollen-producing anthers, D. febrifuga × H. macrophylla hybrids had normal-appearing anthers that produced abundant pollen. F2 and BC1 progeny were obtained using D. febrifuga × ‘Veitchii’ hybrids. This work documents the first step in an effort to combine desirable horticultural features from D. febrifuga and H. macrophylla.