Ch. Darwin QTL (quantitative trait loci) mapping in Pinus sylvestris

Project terminated in 2001.

Estelle Lerceteau and Alfred E. Szmidt

QTL mapping in selection

The development of molecular tools offers new opportunities to assist the traditional forest breeding programs. Using DNA markers, the complex quantitative traits can be resolved into simple Mendelian components or loci, each one being defined as a QTL for quantitative trait locus or locus controlling the expression of a trait. The marker linked to the QTL is then used to follow in a selection process a particular phenotype. If successful, the marker-assisted selection (MAS) would be of a great interest in conifers since it can shorten the evaluation cycle by early screening. The markers may also be included in selection indices, combining both molecular and phenotypic data in a within-family selection or to develop elite lines.

In co-operation with SkogForsk (The Forestry Research Institute of Sweden), we are currently evaluating the stability of QTLs across different genetic backgrounds and environments on P. sylvestris. We have generated two parental linkage maps using AFLP (Amplified Fragment Length Polymorphism) markers. QTLs associated with economically important traits targeted in the Swedish tree-breeding program were detected and located on the maps. For frost resistance we found a QTL of large effect suggesting that a major gene is involved. A cluster of QTLs for tree height, trunk diameter and volume was located on one linkage group, which may suggests pleiotropic effects or linked loci. The QTLs will be validated on a larger sample size and during several years. They will as well be evaluated in other populations before saying how they could be integrated in a MAS strategy. The field evaluations on 500 trees from two crosses have been carried out. This large and unusual sampling size in conifers constitutes an excellent opportunity to test MAS.

QTL for fundamental knowledge acquisition

A QTL study also provides information useful in different areas. First, it gives a better knowledge of the genetics of the traits. An approximation of the number and the effect of the genes controlling the trait can be obtained. This information is of importance in classical selection where the polygenic model assuming a large number of loci of roughly equal and small effects is used. Second, QTL analysis constitutes a new way to study the genetic determinism of developmental processes. In forest trees, a lack of correlation has generally been found between phenotypic evaluations at mature and juvenile stages. Based on QTL studies it has been suggested that different regulatory genes or differential expressions of the same set of regulatory genes might be involved at different stages of maturation. Co-location on a linkage map of a gene and a QTL may be a step forward towards the identification of candidate genes. In order to find such correlation, we will locate on our current maps genes already characterised in P. sylvestris and in related species and some ESTs (Expressed Sequence Tags) from P. taeda or from P. sylvestris. Since ESTs represent a pool of genes expressed in a particular tissue, ESTs and QTLs are a good combination to better understand the genetic control of a physiological process. By mapping the ESTs from P. taeda we will contribute to the international project on genome comparison in conifers aiming at a better understanding of the evolutionary relationships of the genus. These markers will also be used to compare the different genetic maps developed on P. sylvestris and to analyse the synteny within this species.

Selected publications

  1. Lerceteau E., Szmidt A.E., Andersson B. 2000. Detection of quantitative trait loci in Pinus sylvestris L. across the years. Euphytica 121: 117-122
  2. Lerceteau E., Plomion C., Andersson B. 1999. Quantitative Trait Loci (QTLs) for economically important traits in Pinus sylvestris L. Molecular Breeding 6: 451-458.
  3. Lerceteau E., Szmidt A.E. 1999. Properties of AFLP markers in inheritance and genetic diversity studies of Pinus sylvestris L. Heredity. 82: 252-260.
  4. Lerceteau E., Rogers J., Petiard V., Crouzillat D. 1999. Evolution of cocoa bean proteins during fermentation: a study by two-dimensional electrophoresis. Journal of the Sciences of Food and Agriculture. 79: 619-625.
  5. Lerceteau E., Robert T., Petiard V., Crouzillat D. 1997. Evaluation of the extent of genetic variability among Theobroma cacao L. accessions using RAPD and RFLP. Theoretical Applied Genetics. 95:10-19.
  6. Lerceteau E., Quiroz J., Soria J., Flipo S., Petiard V., Crouzillat D. 1997. Genetic differentiation among Ecuadorian Theobroma cacao L. accessions using molecular and morphological analyses. Euphytica. 95:77-87.
  7. Crouzillat D., Lerceteau E., Petiard V., Morera J., Rodriguez H., Walker D., Phillips W., Ronning C., Schnell R., Osei J., Fritz P. 1996. Theobroma cacao L.: a genetic linkage map and quantitative trait loci analysis. Theoretical Applied Genetics. 93:205-214.


by Alfred E. Szmidt