Seed Germination At Different Seed Capsule Maturities to Reduce Stratification Requirement of Japanese Tree Lilac

Woody plant species generally require seed stratification (moist-chilling or moist-warm conditions) to overcome dormancy conditions in the embryo. Seed dormancy is variable in Japanese Tree Lilac [Syringa reticulata (Blume) H. Hara] with a recommendation of 30–90 days stratification at 1°C to 5 °C. Cultivars of Japanese Tree Lilac are propagated either by stem cuttings or by grafting. Grafting is generally done onto seedling rootstocks of S. reticulata seedlings. It would be advantageous to rootstock seedling production to be able to reduce or eliminate the need for seed stratification.  The objectives of this research were to determine time at which seed stratification requirement commences and to determine percent seed germination at different seed capsule maturities. Seed was randomly collected and combined together from 5 different trees every week on the North Dakota State University campus starting on 22 Sept. 2011 for seven weeks (22, 30 Sept; 06, 13, 20, 27 Oct; 04 Nov). Germination test were performed as well as seed moisture content measured weekly.  The germination test consisted of 100 seeds per weekly collected seed samples placed in cell packs containing Sunshine® LC1 mix medium, under natural light conditions, temperature of 21^ºC ± 3, and were hand watered daily. Seed moisture content was measured for each weekly sample using 4 reps of 10 seeds each rep. Germination percentage was highest (90%) at week two and steadily decreased to 0% germination at week 7. Germination percentages were 78.0, 90.0, 78.0, 68.0, 25.0, 1.0, 0.0% for collection weeks 1–7, respectively. Seed moisture content was 58.4, 51.5, 50.0, 56.4, 44.2, 28.6, and 8.9% for collection weeks 1–7, respectively. Germination percentage was directly correlated with seed moisture content and decreased as seed capsule matured (natural drying and splitting of capsule seam to disperse seed) during the fall season. Data suggests that the timing of fall seed collection of Japanese Tree Lilac is critical and must be collected prior to maturation of the seed capsule in preparation for dormancy in order to avoid the need for 30–90 day seed stratification.