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Utility of several connected families for QTL detection
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International audience. As tree improvement is limited by delayed evaluation of performance for quantitative traits, the identification of implicated QTL could provide a valuable tool for early selection. We are developing a method for QTL detection by using connected families from a mating design. The plant material analysed for this study is a factorial mating design involving 12 European larches and 12 Japanese larches. The hybrid families have been evaluated for 11 years for growth and morphological characters and for wood quality (wood gravity assessed by pilodyn and microdensitometry). Genotypes of parental trees are determined at molecular marker loci. Family frequencies for a marker are deduced from parental genotypes for this marker. Statistical relationships between marker frequency and quantitative performance are then investigated. Significant relationships can be validated at an individual level in families showing segregation for the marker. The establishment of genetic maps for each parent (68 markers for the European parent and 81 markers for the Japanese parent) provides spaced markers for further QTL detection. This method for QTL identification presents advantages over the traditional QTL detection which is usually achieved by examining the relationships between marker genotypes and performance of individuals segregating within one family: (i) genotyping is restricted to parents for the whole set of markers and to hybrid families for markers potentially linked to QTL, (ii) the multiplicity of parents increases the probability for at least one family to cosegregate at the QTL and at the associated marker locus, (iii) QTL detected within many families are more suitable for marker-assisted-selection at the level of the mating design.
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