Molecular mapping of the downy mildew and rust resistance genes in a sunflower germplasm line TX16R

The sunflower germplasm line TX16R is resistant to Plasmopara halstedii (causal agent of sunflower downy mildew) and Puccinia helianthi (causal agent of sunflower rust), which are two destructive foliar diseases in sunflower production worldwide. This study reports the mapping of the downy mildew and rust resistance genes Pl 33 and R 16 from TX16R, respectively. Progeny testing of test crosses for downy mildew resistance suggested that Pl 33 localizes to linkage group (LG) 4 of the sunflower genome. Molecular mapping of Pl 33 using simple sequence repeat (SSR) and single-nucleotide polymorphism (SNP) markers identified Pl 33 cosegregating with ORS644, ORS963, SFW04901, and SFW04052, and linking to two SNPs, NSA_006089 and NSA_008496, at a genetic distance of 0.2 cM on the proximal side. Bulked segregant analysis using SSR and EST-SSR markers from LGs previously reported for rust genes identified polymorphic SSR markers associated with rust resistance on LG13. R 16 was mapped between SFW08875 and SFW04317 on LG13, with a genetic distance of 1.8 and 1.1 cM, respectively. The 15 linked markers span a genetic distance of 27.4 cM in LG13. The cosegregating or closely linked markers to the two resistance genes will facilitate marker-assisted selection (MAS) and gene pyramiding, and will further assist in identifying genes responsible for DM and rust resistance.