QTL Mapping Of Leaf Morphological Traits In Poplar Intersectional Hybrid Population

Leaf is the main organ of carbon assimilation and gas exchange in plants,and plays a crucial role in their life history.Leaf morphological traits in Populus spp.are diversiform,and could be used as an early indicator to improve the efficiency of selection.P.deltoides CL.‘Danhong'(DH)was a fast-growing poplar cultivar.Their leaves were large,triangular,and the base of blade were truncated.P.simonii was one of the main native tree species in northern China,with an extensive adaptability and excellent stress resistance.The leaves in P.simonii were small,obovate,and the base of blade were wedge.In this study,DH was used as female parent.P.simonii CL.‘Tongliao1'(TL1)and P.simonii CL.‘Tongliao3'(TL3)selected from natural forest in Tongliao area of Inner Mongolia were used as male parent.F1 progenies were obtained through manual controlled pollination.The morphological indicators of 6,702 mature leaves of 1,261 clones were measured.Multiple statistical methods were used to analyze the genetic variation of leaf morphological traits in progenies.QTL mapping of leaf morphological traits in 422 progenies was accomplished based on DH×TL1 genetic linkage map.The progenies with extremely leaf shape were used to BSA.The main conclusions were listed as follows:(1)The difference of leaf morphological trait in parents was significant.And leaf shape in progenies owned plentifully variation,with typical normal distribution.(2)There were widespread significant correlations(P<0.05)among leaf morphological traits of F1 progenies.Positive correlations with extremely significance(P<0.01)were existed among five indexs(leaf area,leaf perimeter,leaf length,leaf width and petiole length etc.)of leaf size.While for the indexes of leaf shape,petiole length was closely related to the position of leaf maximum width.Variation of leaf width in progenies was the main factor for allometry of blade.Taking leaf area as a dependent variable to make path analysis.The results indicated that leaf width and length was the main determinant of leaf area.Their contributions to the determination coefficients(R2 value)of leaf area were 0.537 and 0.479 respectively.(3)Leaf shape of most progenies was closer to their female parent.For leaf size indexs(such as leaf area,leaf perimeter and petiole length etc.),triennial progenies in the fields showed strong maternal effect,while the annual progenies in greenhouse showed significant paternal effect.Principal component analysis(PCA)was performed with seven directly measured indexes(such as leaf area,leaf length,leaf width and petiole length etc.).Two main factors were extracted,and cumulatively contains 80.19% of leaf variation information.Based on the two-dimensional distributional scatter,we could come to a conclusion that the leaf type of most progenies(92.66%)was intermediate-type between two parents.(4)Seven leaf traits(leaf area,leaf perimeter,leaf length,leaf width,petiole length,length from leaf opex to the widest place and leaf vein angle etc.)were used to QTL analysising.A total of 221 QTLs related to these traits were detected,and distributed on 16 linkage groups,except the 8th,10 th,and 15 th.Contribution rate of these QTLs were ranged from 3% to 6%.In addition,QTLs of different traits were often located on the same genomic region,and these QTLs were extensive pleiotropy.(5)A total of 345 candidate genes related to leaf morphological traits were detected within these QTL interval,mainly participated in these biological processes(such as genome methylation and cell cycle etc.).Two Cyclin family members,which encoded cell cycle proteins,were detected on the QTL which controlling leaf width.A total of 32 candidate genes with leaf type were obtained by BSA.The SMR2 from these candidate genes was detected on the 17 th chromosome,which was likely to involved in cell cycle biological processes.