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Sunflower oil is one of the major sources of edible oil. As the second largest hybrid crop in the world, hybrid sunflowers are developed by using the PET1 cytoplasmic male sterility system that contributes to a 20 % yield advantage over the open-pollinated varieties. However, 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 the newly emerged rust races. The aim of this study was to elucidate the inheritance of rust resistance and male fertility restoration and identify the chromosome location of the underlying genes in Rf ANN-1742. Chi-squared analysis of the segregation of rust response and male fertility in F2 and F3 populations revealed that both traits are controlled by single dominant genes, and that the rust resistance gene is closely linked to the restorer gene in the coupling phase. The two genes were designated as R11 and Rf5, respectively. A set of 723 mapped SSR markers of sunflower was used to screen the polymorphism between HA 89 and the resistant plant. Bulked segregant analysis subsequently located R11 on linkage group (LG) 13 of sunflower. Based on the SSR analyses of 192 F2 individuals, R11 and Rf5 both mapped to the lower end of LG13 at a genetic distance of 1.6 cM, and shared a common marker, ORS728, which was mapped 1.3 cM proximal to Rf5 and 0.3 cM distal to R11 (Rf5/ORS728/ R11). Two additional SSRs were linked to Rf5 and R11: ORS995 was 4.5 cM distal to Rf5 and ORS45 was 1.0 cM proximal to R11. The advantage of such an introduced alien segment harboring two genes is its large phenotypic effect and simple inheritance, thereby facilitating their rapid deployment in sunflower breeding programs. Suppressed recombination was observed in LGs 2, 9, and 11 as it was evident that no recombi

Rust is a serious fungal disease in the sunflower growing areas worldwide with increasing importance in North America in recent years. Several genes conferring resistance to rust have been identified in sunflower, but few of them have been genetically mapped and linked to molecular markers. The rust resistance gene R4 in the germplasm line HA-R3 was derived from an Argentinean open-pollinated variety and is still one of most effective genes. The objectives of this study were to determine the chromosome location of the R4 gene and the allelic relationship of R4 with the Radv rust resistance gene. A total of 63 DNA markers previously mapped to linkage group (LG) 13 were used to screen for polymorphisms between two parental lines HA 89 and HA-R3. A genetic map of LG 13 was constructed with 21 markers, resulting in a total map length of 93.8 cM and an average distance of 4.5 cM between markers. Two markers, ZVG61 and ORS581, flanked the R4 gene at 2.1 and 0.8 cM, respectively, and were located on the lower end of LG 13 within a large NBS-LRR cluster identified previously. The PCR pattern generated by primer pair ZVG61 was unique in the HA-R3 line, compared to lines HA-R1, HA- R4, and HA-R5, which carry other R4 alleles. A SCAR marker linked to the rust resistance gene Radv mapped to LG 13 at 13.9 cM from the R4 locus, indicating that Radv is not an allele of the R4 locus. The markers tightly linked to the R4 gene will facilitate gene pyramiding for rust resistance breeding of sunflower.