| Psathyrostachys juncea is an excellent mowing and grazing grass with strong resistance.It has the advantages of early resuming growth,long greening period,grazing tolerance,trampling resistance,and strong regeneration.It is an excellent grass with great research value and also an excellent germplasm for improving degraded grasslands and cultivating cold and drought resistant forage varieties.P.juncea has low ploidy characteristics and is easier for genetic improvement.Therefore,the analysis of the genetic basis of tiller and seed yield related traits in P.juncea can provide theoretical reference for the breeding of wheat crop.In this study,two clonal populations were established from 300 P.juncea lines from different countries,while all the lines were planted in two locations(Hohhot and Baotou)for four consecutive years(2019～2022).Correlation analysis,principal component analysis,ANOVA,and GGE biplot model were used to analyze the data of phenotypes;The population structure,genetic diversity and linkage disequilibrium of 300 P.juncea lines were evaluated based on SLAF-seq sequencing technology;GWAS analysis of target traits and SNP loci was carried out to explore excellent allelic variations and candidate genes,which provided basic information for germplasm improvement and breeding of P.juncea.The main results are as follows:1.The five tiller-related traits of 300 P.juncea lines showed large variation,the tillering number has the largest variability.Among the eight seed yield-related traits of P.juncea,the seed yield per plant has the largest variability.The phenotypic traits of tiller and seed yield in the associated populations showed a nearly-normal distribution trend.The broad-sense heritability of all traits is above 50%.The tiller number was significantly positive correlation with clump basal diameter(P<0.001),negatively correlation with tiller angle,and positively correlation between plant height and tiller number.Further,correlation analysis of the seed yield factor revealed that seed yield per plant was correlated with multiple traits,and was significantly positive correlated with reproductive tiller number.The results of principal component analysis show that the first five principal components could explain 79.26%of the information.According to the comprehensive performance of the phenotype of 300 lines were classified into four groups.2.The variance analysis of tillering and seed yield traits in two locations over the years showed that the environmental and year effects were the dominant factors affecting the phenotype of P.juncea.The results of GGE biplot model analysis indicated that No.270 and No.283 showed fecundity and stability in tiller-related traits,which from material 502572;No.279,No.287,No.288,and No.297,showed fecundity and stability in seed yield-related traits,which from material 502572 and 598610.The synthesis of tiller and seed yield related traits of P.juncea was found that the material 502572 showed excellent performance in all indicators,which provided a reference value for further research.Considering the discernment and adaptability,Baotou is the ideal test location.3.A total of 1,176,240 SLAF tags were obtained,and 106,337 SNPs were detected on all 21 chromosomes of wheat according to MAF>0.05 and integrity>0.8.The genetic diversity of P.juncea germplasm resources was evaluated based on SNP,and the genetic diversity of P.juncea germplasm was relatively high.Based on population structure,principal component analysis,and NJ tree analysis,300 P.juncea lines can be classified into two different groups based on genotype,which were mainly composed of cultivated and wild varieties.Using genome-wide SNP markers,the LD of the P.juncea germplasm was estimated to be about 100kb,and the LD(r~2)of 21 wheat chromosomes ranges from 0.112(Chr3D)to 0.321(Chr3A),and the LD rapidly declined in the D subgenome.4.Through the GWAS study of five tiller-related traits,51 SNPs loci significantly associated with tiller-related traits were obtained and distributed on 19 chromosomes of wheat.Three loci associated with plant height,with phenotypic variance explained ranging from 5.95%～9.12%;Five loci associated with canopy diameter,with phenotypic variance explained ranging from 5.91%～10.21%;A total of eight loci associated with clump basal diameter were detected that the explained rates of phenotypic variation ranged from5.98%～13.41%;there were 11 loci related to tiller angle,with the explained rates of phenotypic variation ranging from 5.99%～10.54%;and a total of 24 loci related to tiller number were detected,with the explained rates of phenotypic variation ranging from5.98%～13.54%.Among them,eight were consistent with the QTL loci localized by previous authors,and 43 were newly detected loci.Three pleiotropic loci were detected,Chr2B＿489012239 was associated with three traits,canopy diameter,clump basal diameter,and tiller number,which was an important locus for controlling growth and development;Chr2B＿722619144 was associated with clump basal diameter,tiller angle,and tiller number,which was important locus for controlling tillering traits;Chr5B＿551506487 was associated with two traits,clump basal diameter and tiller number.Chr2B＿489012239-AA,Chr2B＿722619144-CC and Chr5B＿551506487-AA were excellent allelic variants of tiller-related traits in P.juncea.The haplotype analysis of potential new loci for tiller-related traits showed that PH-Hap.2,CD-Hap.1,BD-Hap.3,TA-Hap.2 and TN-Hap.2 were excellent haplotypes.The combination of excellent haplotypes could increase the tiller number of P.juncea.Candidate gene analysis was performed on eleven SNPs detected in tiller-related traits in multiple locations,and a total of 42 candidate genes was found,which were involved in cell differentiation and proliferation,phenylalanine metabolism,nitrogen assimilation and plant hormone regulation.5.Through the GWAS study of eight seed yield-related traits,121 SNP loci significantly associated with seed yield-related traits were obtained and distributed on 21 chromosomes of wheat.A total of seven loci significantly associated with reproductive tiller length were detected,with phenotypic variance explained ranging from 5.24%～14.32%;24 loci significantly associated with reproductive tiller number,with the explained rate of phenotypic variation ranging from 4.33%～12.44%;a total of 48 loci significantly associated with spike length were detected,with the explained rate of phenotypic variation ranging from4.44～15.64%;seven loci significantly associated with spike width were detected;six loci significantly associated with spike node number were detected,which could explain5.64%～13.14%of the phenotypic variance;nine loci associated with thousand kernel weight were detected,with the explained rate of phenotypic variance ranging from 4.15%～14.51%;and fourteen SNPs and six SNPs significantly associated with seed weight per spike and seed yield per plant were detected,respectively.A total of 15 seed yield-related SNPs were consistent with the QTL loci localized by previous authors.The distribution of excellent alleles showed that the seed yield traits of P.juncea were improved in cultivars,and the effect analysis indicated that the detected loci could better explain the phenotypic variation.Fifteen pleiotropic loci were significantly associated with multiple traits,RTN,TKW-Hap.4,SL,SY-Hap.4,SL,SY-Hap.3,RTN,SL,SNN,and TKW-Hap.4 were excellent haplotypes.The combinations of excellent haplotypes could improve seed yield of P.juncea.A total of91 candidate genes were found by analyzing the 19 SNPs detected.These candidate genes involve in the synthesis of cell wall polysaccharides and proteins,plant growth and development,photosynthesis,gibberellin regulation,hormone signaling,such as abscisic acid and jasmonic acid,phenylalanine metabolism,and amino acid metabolism processes. |
