Mapeamento de QTLs para qualidade da madeira em Eucalyptus grandis x E. urophylla e ancoragem de clones BAC no mapa genético

Abstract

Species of Eucalyptus are widely planted in continuous forests stands in our country. To increase the competitiveness of our Eucalyptus based forest industry it is imperative to continuously work toward improving the quality of our plantation forestry. The identification of genes or genomic regions controlling traits of interest has been one of the main molecular breeding approaches to this end. Several groups worldwide have started to identify QTLs for some productivity related traits. Most of these reports, however, have used dominant markers that do not allow data sharing and comparison among the various pedigrees and species. QTL information therefore remains restricted to the particular family used in the detection experiment. The use of codominant, multiallelic, highly polymorphic and transferable microsatellite markers, allows, on the other hand, a comparative mapping investigation across multiple pedigrees and even species of the genus. In this work QTLs were localized based on the genetic mapping of 235 microsatellites in a full-sib family of 188 individuals derived form a Eucalyptus grandis x E. urophylla cross. Microsatellite genotyping was carried out by fluorescence detection on the ABI 3100. Individuals were measured at age of three years for volume growth, wood density by pilodyn penetration as well as eleven other traits related to wood properties assessed by Near Infrared Spectroscopy (NIRS). Single marker analysis was carried out using GQMOL and QTLs were declared at a significance threshold of 1%. Composite interval mapping using QTLCartographer was also used after constructing both parental maps by the pseudo-testcross strategy using MapMaker. QTLs were identified for all 14 traits. Several QTLs for correlated traits mapped to the same genomic intervals. For comparative purposes, sib-pair analysis of Fulker and Cardon was also carried out on the integrated genetic map to detect QTL. A general agreement was seen between the two QTL interval mapping analyses. Finally, to contribute for an ongoing effort to anchor the genetic map to physical equivalents of the Eucalyptus genome, for 38 mapped microsatellites one or more BAC clones were identified by library screening. These BAC clones will be used for the construction of a physical map for future efforts of positional cloning of target genes. The use of BAC clones that belong to specific linkage groups as probes for FISH will also allow establishing the correct numbering of linkage groups based on cytogenetic chromosome numbering, information still lacking for species of Eucalyptus.