ARS | Publication request: Chromosome location, DNA markers and rust resistance of the sunflower gene R5

Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 14, 2011
Publication Date: August 3, 2012
Citation: Qi, L., Gulya Jr, T.J., Hulke, B.S., Vick, B.A. 2012. Chromosome location, DNA markers and rust resistance of the sunflower gene R5. Molecular Breeding. 30:745-756.

Interpretive Summary: Sunflower rust, incited by the fungus Puccinia helianthi Schwein., is a serious foliar pathogen affecting sunflower (Helianthus annuus L) in the major sunflower growing regions of the world. In North America, the disease has not been a serious problem for many decades because of successful deployment of effective genes in commercial sunflower hybrids. In the 1980s and early 1990s, however, a change in virulence of the rust race population in North America rendered most of the commercial hybrids susceptible to new virulent races. Amongst the various strategies for rust control, the deployment of diverse sources of resistance in commercial hybrids remains the most effective approach. A germplasm line, HA-R2, carrying the rust resistance gene R5 was released as a multi-race rust resistant line in 1985 and has not been wildly used in commercial hybrid production. R5 remains effective against prevalent rust races of sunflower in North America. This gene was previously reported to be associated with two simple sequence repeat (SSR) DNA markers, ORS316 and ORS630, which were previously mapped to linkage group (LG) 13 of sunflower. However, genetic linkage analysis failed to detect any marker in LG 13 associated with the gene R5. Subsequently, another type of analysis, called bulked segregating analysis, was employed using 510 SSR markers selected from the remaining 16 linkage groups of the sunflower genome. The LG 2 markers showed association with the rust resistance. DNA analysis of 94 F2 individuals with 23 SSR markers from LG 2 confirmed the R5 location on LG 2. R5 was flanked by two SSR markers, ORS1197 and ORS653 at 3.3 and 1.8 cM of genetic distance, respectively. The markers for R5 developed in this study will provide a useful tool to speed up deployment of R5 in sunflower commercial hybrid production.

Technical Abstract: Sunflower rust, incited by the fungus Puccinia helianthi Schwein., has not been a serious problem for many decades because of successful deployment of effective genes in commercial sunflower hybrids in North America. In the 1980s and early 1990s, however, a shift in virulence of the rust race population in North America rendered most of the commercial hybrids susceptible to new virulent races. A germplasm line, HA-R2, carrying the rust resistance gene R5 was released as a multi-race rust resistant line in 1985 and has not been wildly used in commercial hybrid production. R5 remains effective against prevalent rust races of sunflower in North America. This gene was previously reported to be associated with two SSR markers, ORS316 and ORS630, which were mapped to linkage group (LG) 13 of sunflower. However, out of 63 markers mapped to LG 13 screened in the present study, only 18, including ORS316 and ORS630, were polymorphic. These markers, which covered the entire LG 13, were assayed in 94 individual F2 progenies derived from the cross of HA 89 with HA-R2. All failed to detect any marker in LG 13 associated with the gene R5. Subsequently, a bulked segregation analysis was employed with an additional 510 SSR markers selected from the remaining 16 linkage groups of the sunflower genome. The analysis demonstrated that the LG 2 markers showed association with rust resistance. Genotyping of the 94 F2 individuals with 23 polymorphic SSR markers from LG 2 confirmed the R5 location on LG 2, flanked by two SSR markers, ORS1197 and ORS653 at 3.3 and 1.8 cM of genetic distance, respectively. The markers for R5 developed in this study will provide a useful tool to speed up deployment of R5 in sunflower commercial hybrid production.