Effect of germination and water absorption on scarification and stratification of kousa dogwood seed

Abstract

Cornus kousa (kousa dogwood), used as a landscape tree and a source of food and medicine, is difficult to propagate from seeds owing to dormancy. The present study was conducted to develop an effective method of seed propagation and identify the seed dormancy type. Kousa dogwood seeds were classified as presenting physical dormancy (PY) and physiological dormancy (PD) from an immature embryo. Seeds were contained within an impermeable endocarp that conferred PY and had an undifferentiated embryo that grew and differentiated after scarification and cold moist stratification, leading to improved germination. To break PY + PD, four replicates of 50 seeds (3200 in total) for each treatment were prepared by scarification and cold moist stratification. These methods combined improved moisture absorption and germination more than either treatment alone. In particular, the addition of cold moist stratification treatment to scarified seeds could effectively induce embryo development. By contrast, untreated seeds showed low germination rate of less than 1% at 30 °C with continuous light. Sulfuric acid (H2SO4) at different concentrations and durations was used to uniformly wound the endocarp of seeds. Treatment with 80% H2SO4 for 10 min resulted in the highest germination rate (68.6%) and moisture content (65.7%), which were higher than those following polishing with a brushing machine for 5–40 min. Longer treatment with high concentrations of H2SO4 (80 and 100%) caused the acid to infiltrate the seed and inhibit germination by damaging internal tissues, while low concentrations (40 and 60%) did not affect germination rates even after treatment for more than 10 min. To obtain maximum germination, concentration and treatment duration of sulfuric acid should be carefully controlled.