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

Abstract

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 × 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 NDBLOS(sel) × 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.

Fig. 1

High resolution mapping strategy for the identification of informative recombinant lines in cross (cms)HA342 × ARG1575-2. The F₂ population consisted of 2,145 lines and was screened in two steps. First, the whole population was screened with markers ORS610, ORS662 and ORS371 and 188 recombinant lines were selected and, subsequently, genotyped and phenotyped. Second, lines with recombination events between the closely linked flanking markers ORS509, HT244 and HT446 were selfed and homozygous recombinant lines were tested with the four P. halstedii races 730, 100, 330, and 710

Fig. 2

a LG 1 of (cms)HA342 × ARG1575-2 constructed with 2,145 F₂ individuals. b Partial LG 1 map of NDBLOS_sel × KWS04 constructed with 528 F₂ individuals. c Partial LG 1 map of NDBLOS_sel × KWS04 constructed with 2,780 F₂ individuals. Markers with an asterisk were screened in all individuals, while all other markers were screened in recombinant lines only. Pl _ARG is shown in bold. Maps are not drawn to scale and distances on the left side of the map correspond to centiMorgan