Identification of AFLP molecular markers for resistance against Melampsora larici-populina in Populus.

We have identified AFLP markers tightly linked to the locus conferring resistance to the leaf rust Melampsora larici-populina in Populus. The study was carried out using a hybrid progeny derived from an inter-specific, controlled cross between a resistant Populus deltoides female and a susceptible P. nigra male. The segregation ratio of resistant to susceptible plants suggested that a single, dominant locus defined this resistance. This locus, which we have designated Melampsora resistance (Mer), confers resistance against E1, E2, and E3, three different races of Melampsora larici-populina. In order to identify molecular markers linked to the Mer locus we decided to combine two different techniques: (1) the high-density marker technology, AFLP, which allows the analysis of thousands of markers in a relatively short time, and (2) the Bulked Segregant Analysis (BSA), a method which facilitates the identification of markers that are tightly linked to the locus of interest. We analyzed approximately 11,500 selectively amplified DNA fragments using 144 primer combinations and identified three markers tightly linked to the Mer locus. The markers can be useful in current breeding programs and are the basis for future cloning of the resistance gene.