Study On The Regulation Of Endogenous Hormone Apomixis Of Wild Kentucky Bluegrass In Gansu Province

Poa pratensis L.is facultative apomixis plant.In order to study the relationship between apomictic frequency and poly-embryo rate and endogenous hormone content,commercial variety‘MidnightⅡ’and eight wild Kentucky bluegrass with different apomictic frequency in Qingshui,Longxi,Sunan,Gannan,Dingxi,Qinzhou,Lanzhou and Longnan of Gansu Province were used as experimental materials.The paraffin section technique with hematoxylin-eosin double staining was used to analyze and identify the development process of embryo;the characteristics of apomixis of Poa pratensis was expounded;the apomictic frequency was counted and the multiple embryo seedlings of different germplasm resources were counted with the paper germination method to explore the correlation between them.The content of zeatin（ZT）,indole-3-acetic acid（IAA）,zeatin nucleoside（ZR）,gibberellin（GA₃）and abscisic acid（ABA）in the high apomictic frequency and low apomictic frequency germplasms were measured by high performance liquid chromatography;the relationship between endogenous hormone content and apomixis was analyzed,The results of this study will provide some technical references for screening,cultivation and genetic breeding of Kentucky bluegrass.The main results are as follows:1.The paraffin section technique with hematoxylin-eosin double staining was used to identify the development characteristics of embryo sac in kentucky bluegrass at different developmental stages.It was found that the embryo sac developed from the specialized nucellar cells to the nonsporic embryo sac during the development of embryo sac in kentucky bluegrass.The phenomenon of double embryo sac in ovule was more common.In the double embryo sac,there may be all sexual reproduction embryo sac,or the coexistence of sexual reproduction embryo sac and non spore reproduction embryo sac.Of course,there will be three embryo sac in one ovule.According to the statistics of apomictic frequency,the highest rate of apomictic frequency could reach 71.04%,which was Longnan;while the lowest was only11.20%,which was Gannan;the apomictic frequency of other different germplasm resources was relatively small,ranging from 32.00%to 58.00%.The rates of apomixis in Qingshui,Lanzhou,Sunan,Longxi,qinzhou,dingxi were 42.02%,47.80%,51.00%,57.50%,58.60%and 68.58%.2.The paper germination method was used to analyze the germination rate and the poly-embryo rate of kentucky bluegrass in different germplasm resources.The results showed that the germination rate and the poly-embryo rate were different from the collection area.The germination rate of commercial variety‘MidnightⅡ’could be as high as 85.00%.The lowest germination rate in wild germplasm resources was only 14.60%,which was Dingxi;the highest germination rate was 79.80%,which was Longnan;The germination rates of other materials in Gannan,Sunan,Qinzhou,Qingshui,Lanzhou and Longxi were 66.00%,54.40%,76.80%,51.00%,65.60%and67.80%.The range of poly-embryo rate in kentucky bluegrass was 0-15.29%.The highest rate of multiple embryo seedlings was Longnan,which could reach 15.80%;but Gannan had no multiple embryo seedlings,and all of them were single embryo growth.Correlation analysis showed that there was a significant correlation between apomictic frequency and poly-embryo rate（R²=0.96）.3.The high performance liquid chromatography was used to determinate the endogenous hormones content in kentucky bluegrass.Results showed that ZT and ZR contents showed a downward trend at the early stage of spikelet development,which was the lowest at 2 days after heading;then ZT was gradually increased and ZR began to decline after peaking at flowering stage.GA₃ and IAA showed a trend of first increasing and then declining,but GA₃ reached a peak at 2 days after heading.IAA was the highest at flowering stage.In addition,at the early stage of spikelet development,there was no significant change in ABA hormone levels of low-apomictic genotype,but showed a decreasing trend in high-apomictic genotype.However,it was sharply increased from flowering to milk ripening,and then decreased sharply in two genotypes.Correlation analysis showed that the apomixis rate was positively correlated with ZT,ZR,ABA,（ZT+ZR）/IAA and（ZT+ZR）/ABA,negatively correlated with GA₃,IAA/ABA and GA₃/ABA,but failed to correlate with IAA.Therefore,high ZT,ZR and low ABA contents,（ZT+ZR）/IAA and（ZT+ZR）/ABA ratio are more capable of promoting ovule development into apomixis,while high GA₃ content may promote ovule development into sexual pathway.