Dormancy and germination in seeds of the medicinal Asian tree species Phellodendron amurense var. wilsonii (Rutaceae)

The effects of alternating temperatures, cold stratification and gibberellic acid (GA₃) on seed germination of Phellodendron amurense var. wilsonii were investigated. Incubation at 35/10°C or stratification at 4°C prior to incubation of freshly harvested seeds significantly increased germination percentages from less than 5% to greater than 87%. Germination percentage was increased only slightly in intact seeds treated with up to 2000 ppm GA₃. However, partial removal of the seed coat by mechanical scarification plus GA₃ resulted in a drastic increase in both germination percentage and rate. Storage in liquid nitrogen for one and seven months enhanced germination percentage and the beneficial action was due to cracking of the seed coat. Embryos excised from their enclosing tissues and embryos surrounded by endosperm germinated to a much higher percentage than intact seeds, indicating that the water-permeable seed coat plays a mechanical role in preventing radicle protrusion in nontreated intact seeds. Improved germination responses were obtained when the physiological dormant seeds of P. amurense var. wilsonii were pre-treated for 3 months of cold stratification, whilst GA₃ treatments also promoted their germination.