ARS | Publication request: Genetic mapping of HA-R4 identified the downy mildew resistance gene to races 300, 770, and 734

Submitted to: Sunflower Research Forum
Publication Type: Proceedings
Publication Acceptance Date: March 24, 2011
Publication Date: March 24, 2011
Citation: Liu, Z., Gulya, T.J., Seiler, G.J., Vick, B.A., Jan, C.C. 2011. Genetic mapping of HA-R4 identified the downy mildew resistance gene to races 300, 770, and 734. Proceedings of the Sunflower Research Forum, January 12-13, 2011, Fargo, ND. Available: http://www.sunflowernsa.com/research/searchable-database-of-forum-papers/default.asp#r.

Interpretive Summary: Downy mildew is one of the main diseases of cultivated sunflower. The major dominant resistance genes to this disease have been designated as Pl genes. Up to now, more than 23 resistance genes have been reported (Pl1-15, Plv, Plw, Plx-z, Mw, Mx, and PlArg). Ten Pl genes have been mapped to linkage maps using molecular markers. The objective of this study was to molecular map the newly identified downy mildew resistance gene in HA-R4, using an F2 population derived from the cross of HA-R4 x HA 821. HA-R4 was released as a germplasm resistant to Verticillium wilt, four races of rust and two downy mildew races indigenous to North America. HA-R4 is resistant to at least nine downy mildew races including the newly identified Race 734. Two markers tightly linked to the resistance gene cluster, PlHA-R4, were identified, and these markers will be useful for marker-assisted-selection in sunflower breeding.

Technical Abstract: The major genes for sunflower downy mildew resistance have been designated as Pl genes. Many Pl genes have been reported, with 10 of them having been mapped. In this study, we report the molecular mapping of the Pl gene in a downy mildew differential line HA-R4, which has been temporarily named PlHA-R4. It was mapped on the lower end of the linkage group (LG) 1 of the sunflower reference map, with 11 markers covering a genetic distance of 78.9 cM. One dominant marker ORS 1008 co-segregated with it, and another marker HT 636 was at a genetic distance of 0.3 cM proximal to this gene. Marker ORS 1008 was used to test 37 other germplasms. The data suggests that the Pl genes in HA-R4 and HA-R5 are different from other germplasms tested. The two tightly linked markers will be helpful for marker-assisted selection (MAS) in sunflower breeding, as well as molecular cloning of this gene.