QTL Mapping For Morphology Of Different Leaves At Heading Stage And Grain Size And Grain Filling Characteristics At Grain-filling Stages In Barley

Barley(Hordeum vulgare L.)is one of the world’s first domesticated fourth largest grain crops.In barley,the upmost three leaves,particularly the flag leaf,assimilate the most light energy and are main source of generation for carbohydrate production.During the grain filling period,the top two leaves contribute more than 80%of the primary nutrients.Therefore,the analysis of the genetic mechanism for different leaves morphological characteristics in barley can not only provide a theoretical basis for the determination of high light efficiency and ideal plant type of barley,but also has a certain effect on the improvement of barley yield.Grain filling is a complex dynamic physiological process affecting the yield and quality of barley,which determines the grain shape and plumpness index.Grain development is a dynamic process,but previous studies on the genetic mechanism of barley grain shape traits mostly based on the final phenotype after maturity.Studying the genetic characteristics of grain dynamic development and grain filling characteristics is helpful to discover new genes that improve grain morphology and yield,which are important for improving barley yield and molecular marker-assisted selection(MAS).In this study,a high-density genetic map containing 1962 markers was constructed using a double haploid(DH)population of 122 lines to identify QTL for leaf length and area of different leaves(flag leaf,second leaf,third leaf and fourth leaf);detect dynamic QTL for grain shape traits and grain filling characteristics at seven sampling stages from flowering to maturity in barley.The main results were summarized as follows:1. Phenotypic analysis of leaf length and area of different leaves in barley:The phenotypes of 8 leaf morphological traits(flag leaf length,second leaf length,third leaf length,fourth leaf length,flag leaf area,second leaf area,third leaf area and fourth leaf area)were investigated in DH population for two consecutive years.The values of all traits in Huadamai 6 were higher than those in Huaai 11,and the two parents showed significant differences in all traits(p<0.01).The frequency distribution of these traits showed a continuous normal distribution in two years,indicating all traits controlled by multiple genes and can be used for QTL analysis.The variable coefficients of each trait ranged from11.12%to 33.94%within two years.The broad-sense heritability(h _B~2)of all traits ranged from 88.39%to 91.11%,indicating that genetic factors played an important role in determining these traits.2. Phenotypic analysis of grain shape traits and grain filling characteristics in barley:In this study,five grain traits(grain area,grain perimeter,grain length,grain width and grain diameter)and three grain filling traits(grain filling rate,mean grain filling rate and maximum grain filling rate)were phenotyped at seven sampling stages from flowering to maturity in two consecutive years.The value of each trait in Huadamai6 was significantly higher than Huai11(P<0.01)except for GW at stage II.The grain filling rate increased slowly during the initial two stages,after which the grain filling rate increased rapidly and reached its maximum at stage IV,and then decreased continuously.Each trait was continuous variation in all sampling stages,and the absolute values of skewness and kurtosis of most traits were less than 1 except for GFR at stage VII,indicating that these traits follow a normal distribution.The broad-sense heritability(h _B~2)was estimated between58.9%and 98.5%.ANOVA showed statistically significant effects for genotype,environment and G×E interaction with all traits(P<0.01).3. QTL analysis for leaf length and area of different leaves in barley:A total of 57QTLs for top four leaves length and area were detected over two years.The individual QTL accounted for 5.17%-37.11%phenotypic variation and among the 57 QTLs,26 QTLs(46%)were were stably expressed in the both years.Three major stable QTLs(q FLL2-2,q SLL2-2 and q FLA2-2)close to the marker 2HL＿25536047 of 84.5 c M was identified on chromosome 2H.The most important QTL clustered region at M＿256210＿824-2HL＿23335246 on chromosome 2H was associated with all traits except third leaf length.4. Dynamic QTL analysis for grain shape traits and grain filling characteristics in barley:A total of 204 unconditionally identified QTLs for grain area,grain perimeter,grain length,grain width,grain diameter,grain filling rate,mean grain filling rate and maximum grain filling rate were detected on 7 chromosomes,individually accounted for 1.12-78.03%phenotypic variation.Using the conditional QTL mapping method,we detected 95conditional QTLs controlling grain area,grain perimeter,grain length,grain width,grain diameter,grain filling rate,and individually explained 1.26-65.72%of phenotypic variation.Bio Mercator 4.2 was used to integrate unconditional and conditional QTLs identified in different years or stages and to determine the optimal number of consensus QTLs based on meta-analysis method,and 90 unconditional consensus QTLs and 55 conditional consensus QTLs were detected respectively.In addition,to reduce the interference of row type(Rt)and caryopsis type(Ct)on the grain shape and grain filling rate,we used the genome-wide composite interval mapping(GCIM)to perform covariate QTL analysis with Rt,Ct,Rt+Ct as covariates,and detected 118,109 and 84 QTLs on all seven chromosomes,respectively.Comparing the consensus QTLs for grain filling rate and grain size traits detected by the five QTL mapping methods,we identified 34 major consensus QTLs(repeatedly detected in at least two QTL mapping methods).Moreover,certain candidate genes related to grain size,plant height,yield,and starch synthesis were identified in six QTL clusters,and individual gene was specifically expressed in different grain filling stages.The results of QTL for morphology traits of top four leaves at heading stage,such as the stably expressed major QTL at 84.5 c M on chromosome 2H and five QTL clusters that simultaneously affect multiple leaf traits,will provide genetic bases for improving the leaf morphology and molecular breeding of ideal plant types in barley.Dynamic QTL analysis for grain shape traits and grain filling characteristics at different grain filling stages has identified 34 major QTLs and certain candidate genes,which provide useful information for understanding the genetic mechanism of barley grain filling and have a fundamental role in genetic improvement of grain filling characteristics in barley.