Genetic mapping of rust resistance genes in confection sunflower line HA-R6 and oilseed line RHA 397

Abstract

Few widely effective resistance sources to sunflower rust, incited by Puccinia helianthi Schwein., have been identified in confection sunflower (Helianthus annuus L.). The USDA inbred line HA-R6 is one of the few confection sunflower lines resistant to rust. A previous allelism test indicated that rust resistance genes in HA-R6 and RHA 397, an oilseed-type restorer line, are either allelic or closely linked; however, neither have been characterized nor molecularly mapped. The objectives of this study are (1) to locate the rust resistance genes in HA-R6 and RHA 397 on a molecular map, (2) to develop closely linked molecular markers for rust resistance diagnostics, and (3) to determine the resistance spectrum of two lines when compared with other rust-resistant lines. Two populations of 140 F2:3 families each from the crosses of HA 89, as susceptible parent, with HA-R6 and RHA 397 were inoculated with race 336 of P. helianthi in the greenhouse. The resistance genes (R-genes) in HA-R6 and RHA 397 were molecularly mapped to the lower end of linkage group 13, which encompasses a large R-gene cluster, and were designated as R 13a and R 13b, respectively. In the initial maps, SSR (simple sequence repeat) and InDel (insertion and deletion) markers revealed 2.8 and 8.2 cM flanking regions for R 13a and R 13b, respectively, linked with a common marker set of four co-segregating markers, ORS191, ORS316, ORS581, and ZVG61, in the distal side and one marker ORS464 in the proximal side. To identify new markers closer to the genes, sunflower RGC (resistance gene candidate) markers linked to the downy mildew R-gene Pl 8 and located at the same region as R 13a and R 13b were selected to screen the two F2 populations. The RGC markers RGC15/16 and a newly developed marker SUN14 designed from a BAC contig anchored by RGC251 further narrowed down the region flanking R 13a and R 13b to 1.1 and 0.1 cM, respectively. Both R 13a and R 13b are highly effective against all rust races tested so far. Our newly developed molecular markers will facilitate breeding efforts to pyramid the R 13 genes with other rust R-genes and accelerate the development of rust-resistant sunflower hybrids in both confection and oilseed sunflowers.

Map saturation and SNP marker development for the rust resistance genes (R 4 , R 5 , R 13a , and R 13b ) in sunflower (Helianthus annuus L.)

“…The alleles amplified from both R 13a and R 13b lines retain the shared PCR patterns for these two markers, whereas the alleles amplified from R 4 and R 13 could be clearly discriminated by their fragment sizes. In addition, R 4 and R 13 showed differential specificities to rust races (Gong et al 2013b). In the present study, we analyzed reaction of 1104 F 2 plants derived from the cross of HA-R3 (R 4 ) and HA-R6 (R 13a ) to P. helianthi race 336.…”

“…The rust resistance genes, R 4 , R 13a , and R 13b , were previously mapped to the lower end of linkage group 13 of the sunflower genome and closely linked to the common SSR markers ORS316 and ZVG61 (Qi et al 2011b;Gong et al 2013b). The alleles amplified from both R 13a and R 13b lines retain the shared PCR patterns for these two markers, whereas the alleles amplified from R 4 and R 13 could be clearly discriminated by their fragment sizes.…”

“…This line carries a rust R-gene R 4 (Gulya 1985, Miller et al 1988Qi et al 2011b). HA-R6 (PI 607509) is a confection line released by the USDA and the North Dakota Agricultural Experiment Station in 2001 and harbors the rust R-gene R 13a (Miller and Gulya 2001;Gong et al 2013b). Both R 4 and R 13a were mapped to the lower end of linkage group (LG) 13 of the sunflower genome.…”

“…The four F 2 mapping populations derived from the five parental lines were previously used to map the rust Rgenes with SSR markers: R 5 in HA-R2, R 4 in HA-R3, R 13a in HA-R6, and R 13b in RHA 397 (Qi et al 2012a, b;Gong et al 2013b). The inbred line HA 89 was used as a common rust-susceptible parent for these populations.…”

“…These genes are thought to be resistant to the majority of the P. helianthi populations in Australia, Argentina, and North America (Sendall et al 2006;Gulya and Markell 2009;Qi et al 2011a;Friskop et al 2012;Moreno et al 2012;Gong et al 2013b). R 2 was previously positioned to a 28.5-cM interval in LG14 and R 12 a 10.6-cM interval in LG11, resulting in large gaps between the gene and markers on their SSR maps.…”