Seed germination was optimized for ten Hydrangea macrophylla (Thunb.) Ser. and two Hydrangea paniculata Siebold cultivars in vitro. Methods were also developed to assay seed physiology. Best results for in vitro study were obtained with 0.5× Gamborgs solid media in conjunction with Plant Preservative Mixture (PPM), and by sterilizing seed with trichloro-s-triazinetrione (Trichlor). Assays of physiology were conducted by sterilizing seed and treating with combinations of white and red light, cold-treatment, gibberellic acid and potassium nitrate, and light cycles. Estimates of seed viability/dormancy, germination of non-dormant seed, and germination overall were calculated for each treatment combination. The most favorable conditions for overall Hydrangea seed germination were cold-treatment for 6 weeks, imbibition with GA3 + KNO3, and plating on half-strength Gamborgs media supplemented with GA3 in the presence of white light.
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