Identification and characterization of genes contributing to quantitative traits is of utmost importance for plant breeding. Such genes are called quantitative trait loci (QTL). Scientists from the Department of Genetics & Evolution of the Max Planck Institute for Chemical Ecology have now shown that a multitude of QTL influence growth of the model plant Arabidopsis thaliana. Most of these QTL have only minor effect but interact in a complex fashion.

A random 210,000 base pair segment from the Arabidopsis genome was chosen to investigate the influence of allelic variation within this interval on plant growth rate. The interval was dissected in a series of crosses between near-isogenic Arabidopsis lines such that the progeny from each cross segregated in different, very small portion of the genome but not in the flanking regions. Plant growth was determined for more than 7,000 progeny from these crosses. Within this small 210,000 base pair genome segment, two growth rate QTL were identified and, in one case, the responsible gene was cloned. Furthermore, both QTL interacted with other (still unknown) genes in the genome, and phenotypic effects were reversed depending on the genetic background.

Therefore, very many genes, albeit mostly of moderate effect, determine the genetic architecture of complex traits like plant growth or crop yield. In this view, breeding success depends less on selecting single favorable genes but rather on finding the optimal combination of naturally occurring variation within a species.

Jürgen Kroymann, Max Planck Institute for Chemical Ecology