Study On Seed Dormancy,Germination Phenology And Viability Tetrazolium Testing Of Four Iris L.Species

Seeds of Iris tenuifolia,I.tigridia,I.qinghainica and I.songarica were collected from plants growing in Inner Mongolia,Gansu and Qinghai provinces respectively.Seed dormancy characteristics,seed structure,seed size,1000-seed weight,seed embryo morphology,ratio of embryo length to seed length（E/S）were investigated in the laboratory.Seed germination phenology was studied under field burial conditions.Thirteen treatments were used to optimize the preparation of premoistening,exposure of tissues prior to staining and the optimum concentration of tetrazolium solution.The results were as follows:（1）The results of laboratory experiments showed that dormancy percentages of I.tenuifolia,I.tigridia,I.qinghainica and I.songarica were observed 95.9%,86.2%100.0%and 58.4%,respectively.Both of the treatments of drying seed after warm stratification and soaking seeds in GA₃ solution in advance released the seed dormancy of the four irises effectively（P<0.05,N=4）.For I.tenuifolia,I.qinghainica and I.songarica,the dormancy release effect of drying seed after warm stratification was significantly better than that of soaking seeds in GA₃ solution in advance（P<0.05,N=4）.For I.tigridia seeds,there was no significant difference between the two treatments（P>0.05,N=4）.After drying seed after warm stratification,the seed dormancy was reduced by 11.1%,59.0%,13.3%and 52.4%,respectively（P<0.05,N=4）.（2）the results of seed germination phenology experiment showed that all of the four tested iris seeds failed to germinate in the late autumn.However,the buried seeds of I.songarica and I.tigridia began to germinate in the following year in March,and their germination percentages reached its maximum values in March and June respectively.Seeds of I.tenuifolia and I.qinghainica began to germinate in the next year in May,and their germination percentages reached its maximum values in June and August.At the end of the first growing season,there still remained 19.6%,22.0%,78.4%and 60.6%of the viable seed of I.tenuifolia,I.tigridia,I.qinghainica and I.songarica did not germinate,respectively,which indicated that seeds of four tested irises had the ability to form persistent soil seed banks.When the non-germinated seeds of the four tested irises were incubated in lab condition,small portion of the seeds of the four species germinated,which indicated that the environmental factor play a role in the formation of the persistent soil seed banks.In general,the seeds of I.songarica germinated in an orderly pattern,and the seeds of other species germinated in a dispersal pattern.Compared with the control group（before burial）,the E/S values of the seeds of I.tigridia,and I.qinghainica increased significantly after burial（P<0.05,N=10）.After burial,there was no significant change in the values of E/S of I.tenuifolia and I.songarica（P>0.05,N=10）.Compared with the water uptake rate of the seeds before burial,the rate of I.tenuifolia was significantly higher than that of the control group（P<0.05,N=30）.There was no significant change in the water uptake rate of other tested seeds after burial（P>0.05,N=30）.Based on the results of laboratory experiments and seed germination phenology experiments,we preliminarily concluded that the dormancy of the seeds of I.tenuifolia,I.qinghainica and I.tigridia belongs to the morphophysiological dormancy type,and the dormancy of the seeds of I.songarica belongs to the physiological dormancy type.（3）In the anatomy experiment,we observed the seeds of the four irises were composed of seed coat,endosperm,embryo cave and embryo.The seed coat is thick,the endosperm is abundant,the cave opens its door at the end of the micropyle,the space of the cave is slightly larger than the body of the embryo,the embryo does not adhere to the wall of the cave,the radicle end is slightly extended from the cave and covered by thick layer of tissue,the seed coat at the end of the micropyle is uplifted,which is the location of the radicle germinating.The embryos of irises seeds were not typical upright liner embryos,which were milky white,with the inner end obviously curved to the side.There were significant differences in seed embryo sizes among the four irises.The embryo of I.tenuifolia seed was thicker,and that of I.songarica seed was slenderer.（4）The 1000-seed weight,seed length and E/S of the four tested irises seeds were tested as followings.For I.tenuifolia,33.45 g,5.20 mm and 0.41,respectively;For I.tigridia,23.75 g,3.98 mm and 0.32,respectively;For I.qinghainica,13.53 g,3.71 mm and 0.25,respectively;For I.songarica,28.17 g,3.90 mm and 0.42,respectively.（5）For the determination of iris seed viability by tetrazolium solution staining,the seeds need premoistening with H₂O₂ solution,the embryo need take out from seed and stained in a low concentration（0.1%）tetrazolium solution.