Construction Of Genetic Linkage Map Based On EST-SSR And Mapping Of QTLs For The Major Agronomic Characteristics In Sweetpotato(Ipomoea Batatas(L.)lam.)

As the seventh most important crop in the world,sweetpotato produced an estimated 124 million metric tons annually.Sweetpotato is not only a staple food in many developing countries,it is also an alternative source of both industry and bio-energy as a raw material for industry and fuel production.However,sweetpotato,a highly heterozygous,generally self-incompatible,outcrossing polyploid with a large number of small chromosomes(2n = 6x = 90),poses numerous challenges for plant breeding and development of molecular biology.The construction of high-density genetic linkage map is the foundation of gene identification,gene cloning and molecular marker assisted breeding in sweetpotato.The traditional breeding method in sweetpotato is intervariety hybridization and selection.This method are time-consuming inefficient and do not pyramid the derisable genes.In addition,most traits of economical importance in sweetpotato,including many quality and yield traits,are quantitatively inherited,and these traits is possibly negatively correlated each other.Thus,it is difficult to improve quality and yield of sweetpotato through traditional genetic improvement techniques.The rapid development of molecular marker provides an efficient and accurate marker-assisted selection(MAS)technique in sweetpotato breeding.It will facilitate the process of sweetpotato breeding though identification of QTL for important quality and yield traits.In the present study,a composite cross population(CP)was developed from a cross between Wanshu 5 and Shangqiu 52-7 and a genetic linkage map of sweetpotato using EST-SSR markers were constructed.Subsequently,the identifies of quantitative trait loci(QTL)in sweetpotato for storage root dry-matter content,starch content,yield,dry-matter yield and starch yield were carried out.The main results are listed below.1.Polymorphism of EST-SSR markers and genotype identificationA total of 1679 EST-SSR primer pairs were screened with both parents,Wanshu 5 and Shangqiu 52-7,and 672 of them produced good quality polymorphic bands.The polymorphic frequency was 40%.The polymorphic primers were used to genotype the composite cross population and 1022 polymorphic loci were produced.The 1022 loci were used to constructed the genetic linkage map.2?Linkage genetic map constructionThe 1 022 polymorphic loci were used to to construct a framework map at a LOD score ? 5.0 with Joinmap 4.0 software.However,only 350(34.25%)polymorphic markers were located on linkage genetic map.The linkage map included 90 linkage groups with a total lenghth 4 693.21 cM and an average of 13.4cM between adjacent markers.The number of markers in each linkage group ranges from 2 to 47,and the length of each linkage groups ranged from 7.1 to 186.64 cM.3?Comparison between integrated and parental genetic mapThe number of linkage groups,number of markers,coverage of linkage groups and average distance between markers of integrated genetic map were preferable to that of parental maps.Among 90 linkage groups,there are 33 linkage groups related to that of female parent and 39 the linkage groups related to that of male parent,and 18 particular groups belong to the integrated linkage map.Of which,WS.01,WS.02 and WS.54 include two linkage group of one of parent,and the WS.34 linkage group include two linkage groups of that of both parent.4?Identifacations of QTL for major agronomic characteristics in sweetpotatoQTLs controlling major agronomic characteristics were identified based on the genetic map and the measured agronomic trait data in four environment conditions.A total of 64 QTLs of important trait in Sweetpotato were detected.19 QTLs for the dry-matter content,20 QTLs for starch content,9 QTLs for storage root yield,7 QTLs for dry-matter yield,and 9 QTLs for starch yield were identified,and explained 9.0-58.7 %,8.6-66.2 %,26.6-62.3%,10.9-46.8% and 11.8-47.9% of the phenotypic variation,respectively.Among 64 QTLs identified,30,13,and 21 QTLs with a positive effect on phenotypic value were devrived from Wanshu 5,Shangqiu52-7 and two parents,respectively.Four QTLs for dry-matter content(qDMC01.2,qDMC02.1,qDMC07.1,qDMC17.1)and three QTLs for starch content(qSC02.1,qSC03.1,qSC17.1)weredetected in four different environments,Four QTLs for dry-matter content(qDMC03.1,qDMC04.2,qDMC09.1,qDMC11.1)and five QTLs for starch content(qSC01.2,qSC04.2,qSC07.1,qSC14.1,qSC54.1)were identified in three different environments,six QTLs of dry-matter content(qDMC01.1,qDMC06.1,qDMC10.1,qDMC14.1,qDMC24.1,qDMC34.1),seven QTLs for starch content(qSC06.1,qSC07.2,qSC08.1,qSC09.1,qSC10.1,qSC 11.1,qSC34.1),one yield QTL(qy14.1),one dry-matter yield QTL(qDMY01.2)and one starch yield QTL(qSY02.1)were detected in two different environments.These QTLs identified in multiple environments could be used in molecular marker-assisted selection in sweetpotato breeding.