| Agropyron cristatum(L.)Gaertner,an outcrossing perennial grass with the P genome,is a type species of the genus Agropyron in the tribe Triticeae.It includes diploid(2n=14),tetraploid(2n=28)and hexaploid(2n=42),which is widely distributed temperate area of the world.Agropyron cristatum has a strong adaptability in drought,cold,salinity and widely used in soil and water conservation and restoration.Due to the richment in nutrition and good palatability,Agropyron cristatum become a major forage crop husbandry.At the same time,Agropyron cristatum shows strong resistance to some major diseases,such as powdery mildew,rust disease and yellow dwarf,and it is an important resource for wheat and forage genetic improvement.Agropyron cristatum has formed four typical examples of Central Asia population,East Asia population,the Qinghai-Tibet Plateau population,and the Middle East population according to geographical distribution and ecological environment.Because of the natural selection pressure of differentiation,Agropyron cristatum populations were gradually fixed in the adaptive sites,resulting in population differentiation.However,lack of comprehensive understanding of the cytogenetic basis of Agropyron cristatum population differentiation,especially the meiosis chromosome pairing behavior and variation patterns of pollen mother cells,is essentially not conducive to the utilization and protection of Agropyron cristatum resources.In this study,a total of forty-one Agropyron cristatum accessions from Central Asia,East Asia,and the Middle East were sampled.The pollen mother cells were used to prepare chromosomes,and clustering analysis,difference significance analysis,and correlation analysis of each pairing parameter at metaphase Ⅰ of meiosis were conducted.These results are studied to provide cytological basis for the meiotic chromosome pairing variation of pollen mother cells,genetic relationship,origin and evolution of the Agropyron cristatum populations.The main results are as follows:1.In the three populations,the chromosomes of the diploid Agropyron cristatum were mainly paired with bivalent at metaphase Ⅰ of meiosis,no multivalent and a few univalents were observed.The chromosomes of tetraploid Agropyron cristatum in the three populations were mainly paired with bivalent at metaphase Ⅰ of meiosis,a few univalents were observed,and higher frequency multivalent were observed.2.Analysis of statistical clustering found that the forty-one samples of Agropyron cristatum were divided into three clusters.The cluster A contained seven samples of tetraploid Agropyron cristatum from Central Asia population,one sample of tetraploid Agropyron cristatum from East Asia population,and one sample of tetraploid Agropyron cristatum from the Middle East population.The cluster B contained nineteen samples of tetraploid Agropyron cristatum from Central Asia population,four samples of tetraploid Agropyron cristatum from East Asia population,and two samples of tetraploid Agropyron cristatum from the Middle East population.The cluster C contained four samples of diploid Agropyron cristatum from Central Asia population,one sample of diploid Agropyron cristatum from East Asia population,and two samples of diploid Agropyron cristatum from the Middle East population.3.Cluster analysis and difference significance analysis found that:(1)Between the mean parameters of chromosome pairing of Central Asia individuals in cluster A(group 1)and Central Asia individuals in cluster B(group 2),it is interesting to note that difference in the mean number per cell of quadrivalent between group 1 and group 2 was significant(P<0.05),univalent,trivalent,crossover and c-value were highly significant(P<0.01).(2)Between the mean parameters of chromosome pairing of Central Asia individuals in cluster A(group 1)and East Asia individuals in cluster B(group 3),it is discovered that difference in the mean number per cell of univalent,trivalent,quadrivalent,crossover and c-value were extremely significant(P<0.01).(3)Between the mean parameters of chromosome pairing of Central Asia individuals in cluster B(group 2)and East Asia individuals in cluster B(group 3),there is no significant difference in univalent,bivalent,trivalent,hexavalent,but difference in the mean number per cell of crossover and c-value were significant(P<0.05),quadrivalent was extremely significant(P<0.01).4.The parameters of chromosome pairing at meiosis metaphase Ⅰ of Agropyron cristatum were obtained by correlation analysis : the crossover was weakly correlated with univalent and hexavalent,and the correlation coefficients were 0.22 and 0.11.The crossover was positively correlated with the ring bivalent and the closed quadrivalent,and the correlation coefficients were 0.8 and 0.89.The crossover was weakly correlated with the elevation,and the correlation coefficient was 0.19.The ring bivalent,closed quadrivalent and hexavalent are positively correlated with the elevation,and the correlation coefficient increases with the elevation,and the correlation coefficients were 0.16,0.21 and 0.32,while the rod bivalent is negatively correlated with the elevation,and the trivalent is almost not correlated with elevation.5.Based on the results of chromosome pairing configuration of meiosis metaphase Ⅰ,cluster analysis,significance analysis and correlation analysis,it is speculated that the chromosome pairing variation of Agropyron cristatum may be related to different distribution habitats.The evolution and spread trend is spreading from Central Asia to East Asia and the Middle East.In order to overcome the disadvantages caused by environmental changes,Agropyron cristatum has enhanced the adaptability to the new habitat through the mutation of pollen mother cells chromosome pairing at meiosis. |
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