Linkage map development and QTL mapping for leaf rust resistance in the model plant Brachypodium distachyon

The model plant Brachypodium distachyon (L.) Beauv. has been employed to analyze the genetics of resistance to leaf rust. An F2 mapping population of 110 individuals generated between the two B. distachyon diploid inbred lines Bd1-1 and Bd3-1 was used to develop a molecular marker linkage map. The map was mainly AFLP-based. In addition to the initial AFLP framework, conservedmarkers between B. distachyon, barley and wheat, such as EST-derived markers, are currently being developed to be added to the map, thus providing anchor points for comparative genomics studies. To locate quantitative resistance loci on the map, the 110 F2 plants were evaluated for their reactionto the leaf rust Puccinia brachypodii. To improve QTL identification, F2-derived F3 families were tested for resistance to leaf rust in two independent experiments. Disease evaluations showed continuous, quantitative and transgressive segregation. Interval mapping and MQM mapping were performed on the data of the different experiments by using the software MapQTL 5.0 and then QTL positions were compared. Two major genomic regions involved in resistance to leaf rust were detected. Together they accounted for about 40-50% of the observed phenotypic variation. Our results suggest that leaf rust resistance in B. distachyon is a polygenic trait influenced by few majorgenes with large effect as observed in the Triticeae.