Date of this Version
Theor Appl Genet (2012) 125:921–932; DOI 10.1007/s00122-012-1883-x
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 recombination occurred in the introgressed regions of LGs 2, 9, and 11 detected by 5, 9, and 22 SSR markers, 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 Helianthus argophyllus, forming a large rust R-gene cluster of Radv/ R11 /R4 in the lower end of LG13. The relationship of Rf5 with Rf1 is discussed based on the marker association analysis.