Molecular mapping of R11, a novel rust resistance gene in sunflower (Helianthus annuus L

 Sunflower production in North America has recently been threatened by the evolution of new virulent pathotypes of sunflower rust caused by the fungus Puccinia helianthi Schwein. Rf ANN-1742, an ‘HA 89’ backcross restorer line derived from wild annual sunflower (Helianthus annuus L), was identified as resistant to North America rust races 336 (the predominant race over three years) and 777 (the most virulent race). The aim of this study was to elucidate the inheritance of rust resistance and identify the chromosome location of the underlying gene in Rf ANN-1742.  The F2 and F2:3 populations derived from a heterozygous rust resistant plant, 09-519-1, selected from Rf ANN-1742 were inoculated with North America rust race 336. A set of 723 mapped SSR markers of sunflower was used to screen the polymorphism between HA 89 and the resistant plant. The bulked segregant analysis was performed to identify the genomic region harboring the rust resistance gene.  Chi-squared analysis of rust response segregation in F2 and F3 populations revealed that a dominant gene governs rust resistance in the line Rf ANN-1742 and was designated as R11. Bulked segregant analysis subsequently located R11 on linkage group (LG) 13 of the public sunflower genetic map. Based on the SSR analyses of 192 F2 individuals, R11 was mapped to the lower end of LG13 and flanked by ORS728 and ORS45, with a genetic distance of 0.3 cM and 1.0 cM, respectively.  R11 is genetically independent from the rust R-genes R1, R2, and R5, but may be closely linked to the rust R-gene Radv derived from wild H. argophyllus, forming a large rust R-gene cluster of Radv/R11/ R4 in the lower end of LG13. Any combination of the genes R2, R4, and R5 with R11 would give resistance to a majority of rust races and provide protection against the spread of new rust races. The molecular markers closely linked to the R11 gene developed in this study should make this task more feasible, and will allow breeders to effectively select disease-resistant progeny in early segregating generations.