Compatibility Studies in Hydrangea

Abstract

Improvement in cold-hardiness is needed in bigleaf hydrangea (Hydrangea macrophylla). Potential sources of cold-hardiness for enhancing the usefulness of this popular shrub include panicle hydrangea (H. paniculata), smooth hydrangea (H. arborescens), and oakleaf hydrangea (H. quercifolia). The objective of this study was to investigate the possibility of creating hybrids between these three species and H. macrophylla. In addition, self-compatibility of each of the species was evaluated to determine the need for emasculation when making controlled pollinations. Numerous cultivars of the species were utilized in both the self-pollination and interspecific hybridization studies. Number of flowers self-pollinated ranged from 1000 in H. arborescens to 3000 in H. quercifolia. Viable seeds were obtained from all species except H. arborescens. All five of H. quercifolia, 9 of the 18 H. paniculata, and 1 of the 8 H. macrophylla self progeny obtained survived. Emasculation of Hydrangea flowers to be used in controlled pollinations is therefore recommended. Seedlings were obtained from all interspecific crosses in which H. macrophylla was used as the maternal parent. All putative hybrid seedlings died either at the cotyledonary stage or while the first set of true leaves was expanding.