The Dormancy And Germination Physiology Of Manchurian Ash Seeds In Different Development Stage

Dormancy and germination are two important stage in seed life cycle.The study on regulation techniques and its mechanism for seed dormancy and germination let us well understand and use seed ecophysiological characters to guide seedling growing practice. Fraxinus mandshurica Rupr.is an important and valuable hardwood species in Northeast China,and seed propagation is its main propagation method.The ecophysiological characters of seed dormancy and germination of Fraxinus mandshurica during seed development, stratification,natural burying and germination were studied and discussed for the purpose of providing theoretical basis and technique reference to establishment of the functional, economic,fast,and effective methods for breaking seed dormancy and promoting seed germination of Fraxinus mandshurica.The main results were as follows:(1) The ABA content,inhibition activity and embryo germination ability of Fraxinus mandshurica seeds presented fluctuation pattern in different time of seed development till maturity,which is suggested that seed dormancy degree was fluctuated in this process.The seeds of Fraxinus mandshurica reached morphological maturity status at 110 to 120 days after flowering,and the seeds collected during this time could germinate normally after stratification, thereby,seed collection ahead of regulation required schedule for Fraxinus mandshurica is feasible.Stratification at 5℃for 12 weeks following at 20℃for 16 weeks is better for seeds collected ahead of schedule to break dormancy,and the earlier the development time of the collecting seeds,the more warm pretreatment time needed to finish seed embryos growth. Prolonged warm pretreatment for Fraxinus mandshurica seeds collected ahead of schedule had evident effect on improving the subsequent seed germination.(2) In process of Fraxinus mandshurica seed stratification,pericarp acted as an inhibitor, and pericarp removing promoted embryo growth and the subsequent seed germination. Washing also promoted embryo growth and the subsequent seed germination,and the feasible time for washing before seed stratification was 96 hours.Dealing with proper plant growth regulators before seed stratification could get good pretreatment effect.Treating with 100 mg/L GA₃ promoted the subsequent seed germination,but not the embryo growth,whereas treating with 1 mg/L BA promoted not only the embryo growth but also the subsequent seed germination.(3) The better temperature for Fraxinus mandshurica seed warm stratification was 15℃,it was favorable for the embryo growth and seed germination.When seed stratificated in sand or no medium,pretreatment at cold for 3 months following 3 months at warm could get better germination.Naked stratification(without medium) for Fraxinus mandshurica seed is feasible, and the seed moisture content within 45%-50%in cold pretreatment stage was better for seed germination.(4) Seeds sowing in pre-year summer for Fraxinus mandshurica fresh seed is not feasible, but the stored seeds could emerge by this method.The sowing time sould be arranged berfor September,and seed dormancy would not be broken if the sowing time was too late.If seeds sowed in May or June,the sowing bed should be irrigated in time.The emergence rate of Fraxinus mandshurica seed sowing in pre-year summer was also effected by seed quality, climate of the sowing year and other factors.Dealing with proper plant growth regulators before seed sowing in pre-year summer had good effect on seed germination.Treating with 10 mg/L GA₃,1 mg/L BA or 100 mg/L KT for one day could get better germination results.The action of KT was investigated,and the results indicated that KT treatment promoted embryo growth and endogenous hormone(GA₃,ZT,and ABA)changing to the status in favor of seed germination.(5) Statified Fraxinus mandshurica seed germinated better under alternating termperature regimes than that under constant temperature regimes.The optimum alternating and constant temperature regimes were 15℃/10℃and 10℃respectively,and a constant regime over 20℃would induce secondary dormancy.Incubation at this temperature for at least 3 days inhibited seed germination over the temperature regime 15℃/10℃,temperature previously suitable for germination.When germination under high temperature,endogenous hormone of statified seeds changed to the status in favor of seed dormancy,thereby some metabolization processes for germination were inhibited,and seed could not germinate.When germination under suitable temperature,dealing with plant growth regulators had no obvious effect on seed germination.But,when germination under high temperature,dealing with plant growth regulators promoted the subsequent seed germination and the decrease in germination level was delayed.The reason for secodary dorancy were investigatied,and the results suggested that the embryo was not dormant,but the endosperm played an important role in the induction of secondary dormancy at high temperature.Desccation and cold treatment were not good methods for secondary dormancy releasing of Fraxinus mandshurica seed.However,dealing with 1.0 mmol/L ethephon or GA₄₊₇ released seed dromancy preferably.The action of ethephon in releasing secondary dormancy was that it promoted endogenous hormone changing to the status in favor of seed germination,and recovered metabolization processes for germination, ultimately the seed germinated.