Fine mapping of the sunflower resistance locus Pl ARG introduced from the wild species Helianthus argophyllus

Downy mildew, caused by Plasmopara halstedii, is one of the most destructive diseases in cultivated sunflower (Helianthus annuus L.). The dominant resistance locus Pl (ARG) originates from silverleaf sunflower (H. argophyllus Torrey and Gray) and confers resistance to all known races of P. halstedii. We mapped Pl (ARG) on linkage group (LG) 1 of (cms)HA342 x ARG1575-2, a population consisting of 2,145 F-2 individuals. Further, we identified resistance gene candidates (RGCs) that cosegregated with Pl (ARG) as well as closely linked flanking markers. Markers from the target region were mapped with higher resolution in NDBLOSsel x KWS04, a population consisting of 2,780 F-2 individuals that does not segregate for Pl (ARG) . A large-insert sunflower bacterial artificial chromosome (BAC) library was screened with overgo probes designed for markers RGC52 and RGC151, which cosegregated with Pl (ARG) . Two RGC-containing BAC contigs were anchored to the Pl (ARG) region on LG 1.