Submitted to: Journal of Environmental Horticulture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/6/2009
Publication Date: 7/1/2010
Citation: Greer, S.P., Reed, S.M., Rinehart, T.A. 2010. Dormancy and Germination In Vitro Response of Hydrangea Macrophylla and Hydrangea paniculata Seed to Light, Stratification, and Gibberellic Acid. Journal of Environmental Horticulture. 28(1):41-47.2010. Interpretive Summary: For over three centuries, traditional breeding of Hydrangea has relied heavily upon observed occurrences of spontaneous mutation and chance seedlings; more recent work has sought to increase phenotypic diversity through influx of new germplasm, wide crosses, and mutagenesis. Limitations innate to all of these methods include cultivar, species and subspecies incompatability, sterility, lack of progeny germination, and the lack of progeny vigor. These limitations have been amplified as a result of only anecdotal knowledge of Hydrangea seed physiology and the lack of in vitro methods to optimize and track seed germination. To facilitate progress in understanding Hydrangea seed physiology we developed in vitro methods to assay Hydrangea seed viability, dormancy, and germination; we then subjected open-pollinated H. macrophylla and H. paniculata seed from 12 cultivars to series of sterilization, media, stratification, chemical, and light treatments, assaying these treatments individually and at times in combination with one another, in order to establish optimal conditions for their initial propagation in vitro.
Technical Abstract: Seed germination was optimized for ten Hydrangea macrophylla cultivars and two Hydrangea paniculata cultivars in vitro. Methods were also developed to assay seed physiology. Best results were obtained with 0.5X Gamborgs solid media in conjunction with Plant Preservative Mixture (PPM), and by sterilizing seed with trichloro-s-triazinetrione (Trichlor). Sterilized seed were treated with combinations of white and red light, stratification, gibberellic acid and potassium nitrate, and light cycles. Using digital imaging, estimates of seed viability/dormancy, germination of non-dormant seed, and germination overall were calculated for each treatment combination. The most favorable conditions for Hydrangea seed germination were stratification for 6 weeks, imbibation with GA3+KNO3, and plating on half-strength Gamborgs media supplemented with GA3 in the presence of white light.