Molecular mapping of the Pl 16 downy mildew resistance gene from HA-R4 to facilitate marker-assisted selection in sunflower

The major genes controlling sunflower downy mildew resistance have been designated as Pl genes. Ten of the more than 20 Pl genes reported have been mapped. In this study, we report the molecular mapping of gene Pl(16) in a sunflower downy mildew differential line, HA-R4. It was mapped on the lower end of linkage group (LG) 1 of the sunflower reference map, with 12 markers covering a distance of 78.9 cM. One dominant simple sequence repeat (SSR) marker, ORS1008, co-segregated with Pl(16), and another co-dominant expressed sequence tag (EST)-SSR marker, HT636, was located 0.3 cM proximal to the Pl(16) gene. The HT636 marker was also closely linked to the Pl(13) gene in another sunflower differential line, HA-R5. Thus the Pl(16) and Pl(13) genes were mapped to a similar position on LG 1 that is different from the previously reported Pl(14) gene. When the co-segregating and tightly linked markers for the Pl(16) gene were applied to other germplasms or hybrids, a unique band pattern for the ORS1008 marker was detected in HA-R4 and HA-R5 and their F(1) hybrids. This is the first report to provide two tightly linked markers for both the Pl(16) and Pl(13) genes, which will facilitate marker-assisted selection in sunflower resistance breeding, and provide a basis for the cloning of these genes.