Genetic Structure And Physiology Of Drought Resistance In The Population Of Psammochloa Villosa

Psammochloa villosa is a typical rhizome sammophytic herb of the genus Psammochloa in Poaceae,which is mainly distributed in Inner Mongolia Plateau and adjacent sandy areas.Due to its soft grass quality and high nutritional value,P.villosa is an important forage in desert areas of midwestern China.Based on microsatellite molecular markers and physiological indicators,this study jointly explored the genetic structure and drought adaptation mechanism of P.villosa,and provided reference for the protection and utilization of this species,improvement of forage varieties and breeding of new varieties.The main findings were as follows:?To analyze the genetic structure of P.villosa,we screened out 13 primers pairs with higher polymorphism based on the transcriptome data.We detected that the percentage of polymorphism in SSR loci was 77.1%;the number of alleles was 104;and the number of alleles at each locus ranged from 3 to 14,with an average of 8.According to the genetic diversity index of 13 primer pairs,the indices of the number of effective alleles(N_e),Shannon's information index(I),and the value of PIC ranged from 1.362 to 2.546 with an average of 1.776,0.278 to 0.946 with an average of 0.567,and 0.317 to 0.747 with an average of 0.511,respectively.The above results indicated that,these 13 primers showed high levels of polymorphism of P.villosa.?The average observed alleles of P.villosa were 2.140,which the observed alleles and private alleles of P31 were the highest with 3.462 and 0.462,respectively.The gene flow(Nm)and the coefficient of genetic differentiation were from 0.097 to 1.956 with an average of 0.675,and 0.113 to 0.721 with an average of 0.356.These results indicated that there were lower gene exchanges and greater genetic differentiation among populations,which was consistent with the results of AMOVA analysis that the genetic variation among populations(58%)was greater than within populations(42%).The results of Mantel test showed that there was a significant positive correlation between genetic distance and geographic distance(r=0.291,P=0.010),which further confirmed the results of AMOVA analysis.The average F index of population level was-0.360,showing an excessive amount of heterozygosity,which indicated that P.villosa had a strong adaptability to the environment during the evolution process.?Based on Bayesian clustering analysis,39 populations of P.villosa were divided into two groupsnamed Group1 and Group2,which were located on both sides of the Yinshan Mountains.Among them,Group2 gene pool was dominant and included most of populations,which was consistent with the results of PCo A and UPGMA cluster analysis.It is considered that strong adaptability to the environment is the main reason for the existing genetic structure.In addition,the analysis results of PCo A and UPGMA indicated that the genetic relationship among populations close to each other was not necessarily close.?Under 0%,10%and 20%PEG-6000 stress,there were significant differences in germination rate(P<0.05).With the increase of PEG-6000 concentration,the germination rate,germination potential,vigor index,bud length and drought-resistant germination index all showed a gradually decreasing trend,while the germination index showed a trend of first decreasing and then increasing.?The relative germination rate,relative germination potential,germination drought resistance index and drought resistance activity index were highly significantly correlated(P<0.01).Therefore,they could be used as important indexes for drought resistance evaluation of P.villosa.Based on the evaluation results of drought tolerance membership function value and UPGMA clustering results at germination stage,the germplasm resources with strong drought resistance were selected from P4 population(comprehensive drought tolerance value of 0.748)and P7 population(comprehensive drought tolerance value of 0.953)from Sunid Left Banner of Inner Mongolia.?There were significant differences in 6 physiological indexes(SOD activity,POD activity,MDA content,chlorophyll A content,chlorophyll B content and total chlorophyll content)at seedling stage under different PEG-6000 concentrations(P<0.05).With the increase of drought stress,POD activity,MDA content,chlorophyll A content,chlorophyll B content and total chlorophyll content all showed an increasing trend,while SOD activity showed an increasing trend at first and then a decreasing trend.The calculation of membership function values of six physiological indexes showed that the P16 population from Alxa Right Banner of Inner Mongolia(comprehensive drought tolerance value of 0.630)had the strongest drought resistance.?The correlation analysis between 22 geographic climate factors in the natural population of P.villosa and 6 physiological indexes in the seedling stage showed that the MDA content was significantly positively correlated with altitude factors,and significantly negatively correlated with climate factors such as the average annual temperature deviation(bio7)(P<0.01).Principal component analysis(PCA)showed that the altitude was positively correlated with the average temperature in the wettest season(bio8),and the climatic factors such as the dryest month rainfall(bio14)contributed the most to the geographical distribution of the P.villosa.The results of Redundancy analysis(RDA)showed that nine geographical and climatic factors such as the altitude of the population significantly affected the physiological characteristics of the seedlings.POD activity,SOD activity,MDA content and chlorophyll content were higher in high temperature,high altitude and high latitude populations.It was proved that the geographical distribution of wild germplasms was different,and the tendency of SOD activity,POD activity,MDA content and chlorophyll content of germinated seedlings was different.