Study On Genetic Diversity And Chlorophyll Fluorescence Characteristics Of Thymus L. In Shanxi Province

Thymus L.have short plants,bright flowers,long flowering and green periods,fast growth and reproduction with stolons,strong drought tolerance,barren tolerance and cold tolerance to the environment,and can be used as excellent aromatic ground cover plants in urban landscape ecological construction.In this study,the adaptability and evolutionary potential of Thymus L.plants from 8 provenances(HY,ZZ,YY,ZY,FS,XX,QY and PX)in Shanxi Province were analyzed by chlorophyll fluorescence characteristics,leaf phenotypic characteristics and genetic diversity at molecular level.It provides a solid theoretical basis for the establishment,preservation,development and utilization of Thymus L.germplasm resources,introduction and breeding of new varieties in Shanxi Province.The main results are as follows:The chlorophyll fluorescence parameters and light response curves of Thymus from different provenances were measured by PAM-2500 modulated chlorophyll fluorescence meter.(1)With the increase of light intensity,the r ETR of Thymus L.from eight provenances increased first and then decreased.When the light intensity was 1500 μmol·m-2·s-1,the r ETR values of Thymus L.from different provenances reached the maximum,indicating that under light intensity.(2)The chlorophyll fluorescence characteristics of Thymus L.from different provenances were significantly different(P<0.05).The mean values of chlorophyll fluorescence parameters Fm,Fv/Fm,Y(II),ETR,q P,NPQ,Y(NPQ),Y(NO)of Thymus L.were 1.334,0.772,0.703,5.905,0.916,0.058,0.017 and 0.280,respectively.The chlorophyll fluorescence of Thymus L.from different provenances has a large variation range and a high degree of variation,which is rich in diversity.Among them,chlorophyll fluorescence variation ranged from 1.31% to 22.95%,NPQ variation was the largest and Fv/Fm variation was the smallest.The variation degree of FS,XX and QY was greater than the total variation mean,which indicated that the variation degree of these three provenances was greater and the diversity was higher than that of other provenances.Fo,Fm,Fv/Fm and q P were only significantly correlated with geographical factors,and were greatly affected by geographical environment.Cluster analysis showed that Thymus L.from eight provenances could be divided into three44categories: QY,PX,ZZ,ZY,FS,HY and other six provenances.Fo,Fm,Fv/Fm,Y(II),q P and ETR werehigher,while NPQ,Y(NPQ),Y(NO)were lower,which indicated that Thymus L.had strong ability to absorb and transform light energy and had high photosynthetic efficiency.The results showed that the excellent photosynthetic characteristics of thyme could be used for breeding of good varieties.The second type is YY,which has moderate photosynthetic efficiency and general light protection ability.It can be considered to develop and utilize in areas where light is suitable.The third type is XX.Compared with Thymus from other provenances,the overall photosynthetic capacity of thyme leaves is weaker.Leaf shape index(leaf length,leaf width,leaf area)was measured by leaf area meter,and leaf shape index was calculated.The microscopic morphological indexes(upper and lower epidermis,palisade tissue,spongy tissue)of leaves were measured by paraffin section method,and the leaf porosity and tightness were calculated.There were significant differences in leaf morphological traits of Thymus L.from different provenances(P<0.05).And the genetic variation coefficient of leaf morphology is large,the variation range is large,and the variation degree is high,which has rich genetic diversity of leaf phenotype.The genetic variation coefficient of leaf area was 29.76% and that of lower epidermis was only 3.33%.The variation range of leaf morphology was 1.64%~12.59%.The variation degree of lower epidermis was the largest and that of leaf thickness was the smallest.The coefficients of variation of provenances FS,ZZ and XX were higher than the mean of total variation(6.31%),which indicated that the three provenances had greater variability than other provenances,and the diversity of leaf phenotypes was more abundant.The correlation analysis showed that leaf area was positively correlated with leaf length,leaf width and annual precipitation,negatively correlated with longitude and annual sunshine hours,and positively correlated with leaf tightness and elevation.Cluster analysis showed that eight provenances could be divided into three categories: YY,PX,ZY,FS,HY and other five provenances,QY and XX,and ZZ thyme with slender leaves,larger leaf area,thicker leaves and larger porosity.The genetic diversity of Thymus from 8 provenances in Shanxi Province was studied by using ISSR molecular markers.123 primers were amplified with 12 ISSR primers,and the polymorphic bands were as high as 85.37%.The average values of allele number,effective allele number,Nei’s gene diversity,Shannon’s index and polymorphic locus ratio of Thymus from 8 provenances were 1.4563,1.3063,0.1765,0.2607 and 45.63 respectively.The genetic diversity level of Thymus was QY > PX > XX> FS> YY> ZY >ZZ > HY.The total genetic variation of Thymus is 50.86% in Provenances and 49.14% among provenances.Based on Nei’s genetic distance,the genetic relationships of Thymus from eight provenances were clustered and divided into two categories: QY,XX and PX,and the other five provenances were clustered.The genetic distance between QY and ZZ was 0.3621,the genetic difference was large,and the genetic relationship was far.