A high density genetic map of maritime pine based on AFLPs

We constructed a high-density linkage map of maritime pine (Pinus pinaster Ait.) based on AFLP (Amplified Fragment Length Polymorphism) markers using a three-generation outbred pedigree. In a first step, male and female maps were established independently with test-cross markers segregating 1: 1 (presence: absence of the amplified fragment in the full-sib progeny). In a second step, both maps were merged using intercross markers segregating 3: 1 in the progeny. A combination of MAPMAKER and JOINMAP softwares was used for the mapping process. A consensus map was obtained and is available at URL http:// www. pierroton. inra. fr/genetics/pinus/ Map3/ index. html. It covers 1441 cM and comprises a total of 620 AFLP markers on 12 linkage groups. The physical size of the maritime pine genome (51.5 pg/2C) was measured by flow cytometry, providing a physical/genetic size ratio of 13.78 Mb/cM. This map will be used to dissect the genetic architecture of economically (growth, wood quality) and ecologically (water-use efficiency) important traits into mendelian inherited components (QTLs: Quantitative Trait Loci). It will also provide a framework to localize more informative markers (ESTs: Expressed Sequence Tags) to be used as candidate genes in QTL detection experiments. The location of orthologous markers (ESTs and SSRs: Simple Sequence Repeats) will also allow the study of the genome structure of closely related conifer species using a comparative genome mapping approach.