Study On Seed Dormancy Characteristics And Dormancy Breaking Of Cotoneaster Horizontalis And C. Multiflorus

Cotoneaster horizontalis and C.multiflorus are excellent flowery and fruitful shrubs in landscaping.However,naturally it takes 1-2 years for their seeds to germinate from dormancy breaking.In order to determine the dormancy types of the two species seeds and find the best way to break dormancy,this study observed the anatomical structure and water permeability of the fruit shell,the development process of the embryo and the germination rate of the fruit shell acid erosion combined with cold stratification treatment.This study also measured the changes of physiological and biochemical indexes in the stratification process of two species and the changes of physiological indexes during the seed germination of C.horizontalis.The main results were as follows:1.The fruit of C.horizontalis had 2-3 separate pits,containing 0-1 seed;C.multiflorus had only 1pit,containing 0-2 seeds.The embryos of the two species were not fully developed when the fruits matured naturally.The main manifestation was that there were no obvious vascular bundle area at the hypocotyls,and the germs were only composed of 2-3 layers of cells.According to the dichotomy index proposed by Baskin and Baskin（2014）,the seed dormancy type of C.horizontalis and C.multiflorus was determined to be morphophysiological dormancy.2.The fruit shells of C.horizontalis and C.multiflorus had permeable and mechanical obstacles to seed germination.They were composed of stratum corneum,wax layer and sclereid layer.The sclereid layer increased the hardness and thickness of the fruit shell.Their structure seriously hindered the seed water absorption and the radicle protruding.The fruit shells of C.multiflorus had an extra sclereid layer comparing with C.horizontalis,so the hindering effect was more serious.3.Treatment with 98%concentrated sulfuric acid could only break the obstructive effect of the friut shells.Combining 4°C or natural low-temperature stratification treatment after acid erosion was the best way to break the seed dormancy of the two species of Cotoneaster.After acid erosion,the germination rate of C.multiflorus reached 64%combing with 150 days stratification,and the germination rate of C.horizontalis reached 84%combing with 60 days stratification.However,the effect of GA₃and 6-BA on the dormancy of C.horizontalis seeds was not obvious.4.The embryo gradually matured during cold stratification treatment.And after 40 days of stratification,the embryos would developed into cotyledon embryos.In this process,the soluble sugar and starch content of C.horizontalis seeds showed a decreasing-increasing-decreasing trend,and the soluble protein content firstly decreased and then increased.The activity of SOD enzyme showed a trend of increasing-decreasing-increasing,and the changes of these indexes provided the material and energy basis for embryo development and dormancy release.The MDA content had accumulated slightly,but it did not cause serious damage to the embryo.Different from the seeds of C.horizontalis,the soluble protein content and SOD enzyme activity of C.multiflorus did not show an upward trend in the later stage.This may be due to the longer cold stratification time of C.multiflorus.In the process of cold stratification,the decrease of ABA and IAA content and the increase of GA₃/ABA ratio may promote the release of dormancy of the two Cotoneaster seeds.The content of GA₃ had been showing a downward trend.It was speculated that the release of dormancy of the two Cotoneaster seeds was not affected by GA₃.5.During the germination process of C.horizontalis seeds,the soluble sugar,starch,and soluble protein content all decreased significantly,indicating that the seeds decompose their own storage materials to obtain the nutrients and energy needed during the germination process.The activity of SOD and POD enzymes continued to increase,thereby protecting the seeds from germinating smoothly.