Integration Of EST-CAPS Markers To Linkage Maps And Detection Of QTLs Related With Rooting Ability Of Cuttings And Field Growth In Eucalyptus

Eucalyptus urophylla and E. tereticornis are two important plantation tree species aroundthe world. Linkage map construction and QTL detection based on molecular markers havebeen a focus in the research field of woody plant genomics in recent years. The availability ofa wealth of expressed sequence tags (ESTs) for many species, in publicly accessible databasesin particular, has facilitated the development of sequence tagged site (STS) markers, such asEST-derived simple sequence repeats (EST-SSR), insertion/deletion (EST-indel) and singlenucleotide polymorphism (EST-SNP).In this study, a suite of91ESTs derived cleaved amplified polymorphic sequence (CAPS)markers were validated and used for enriching the genetic maps of E.urophylla and E.tereticornis built previously based on random amplified polymorphic DNA (RAPD) markers.For E. urophylla,48CAPS markers are integrated into the map, the total map extended to1,789.5cM, and the mean interval between markers was9.7cM, being284.9cM larger and1.3cM less than those of the prior RAPD based map, respectively. For E. tereticornis,42CAPS markers are integrated into the map, the total map spanned1,488.1cM, and the meanmarker interval was10.3cM, being452.4and0.2cM more than the prior map, respectively.All the77newly mapped EST-CAPSs (13markers in common between the two parents) foundeach at least one homologue in the E. grandis genome sequence released recently, andconserved synteny and colinearity were observed between E. grandis genome and our linkagegroups.Rooting ability of cuttings and field growth are two of the most important traits targetedfor clone selection in Eucalyptus. In this study, we used a F1pedigree of E. urophylla×E.tereticornis to detect quantitative trait loci (QTLs) controlling four cutting-related traits,number of roots per cutting, the maximum length of roots and percentage of rooted cuttingsand root dry weight,,as well as two growth traits, height (H) and breast-high diameter (DBH) at13,18and46months of age. For cutting-related traits, six and five QTLs were detected ongenetic maps of maternal E. urophylla and paternal E. tereticornis, respectively, with LODvalue ranging from2.0to3.9, variance explained from15.2to26.8%. For growth traits, twoand one QTLs were detected on the maternal map in46-month-old H and D,respectively.Totally, there are three QTLs related to the new validated CAPS. No QTL wasfound to affect significantly the rooting ability of cuttings and field growth simultaneously,implying probably the difference in genes responsible for the two types of traits.Several markers had zero cM of map distance to or linked very closely with QTL, whichmight act as sound candidate markers for future marker-assisted selection in related traits. Theenriched maps would provide a set of useful markers for genome analysis, comparativemapping, and fine-mapping of important genes located in conserved regions for the importanttree genus Eucalyptus.