ARS | Publication request: Molecular mapping of the rust resistance gene R4 to a large NBS-LRR cluster on linkage group 13 of sunflower

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 31, 2011
Publication Date: June 15, 2011
Repository URL: http://naldc.nal.usda.gov/catalog/49851
Citation: Qi, L., Hulke, B.S., Vick, B.A., Gulya, T.J. 2011. Molecular mapping of the rust resistance gene R4 to a large NBS-LRR cluster on linkage group 13 of sunflower. Theoretical and Applied Genetics. 123(2):351-358.

Interpretive Summary: Rust is a serious fungal disease in the sunflower growing areas worldwide with increasing importance in North America in recent years. An economic and environmentally friendly method to control rust is to use resistant cultivars and hybrids. Incorporating multiple resistance genes into a single cultivar, referred to as 'gene pyramiding', will achieve greater resistance durability. However, the selection of the parental lines with various resistance gene combinations is difficult by conventional methods. Mapping rust resistance genes and developing robust molecular markers will facilitate this breeding approach and add precision to selection. Several genes conferring resistance to rust have been identified in sunflower, but few of them were genetically mapped. The rust resistance gene R4 in the germplasm line HA-R3 was derived from an Argentina open-pollinated variety and is still one of most effective genes. We have used DNA markers previously mapped to linkage group (LG) 13 to screen for polymorphisms between two parental lines HA 89 and HA-R3. Genetic linkage analysis of an F2 segregating population derived from the cross of HA 89 with HA-R3 indicated that two markers, ZVG61 and ORS581, are tightly linked to the R4 gene. These two markers were located on the lower end of LG 13 within a large cluster of genes identified previously as possessing disease resistance. The PCR pattern generated by marker ZVG61 is unique in the HA-R3 line compared to lines HA-R1, HA-R4, and HA-R5 which carry other R4 alleles. Another type of DNA marker (SCAR marker) known to be linked to the rust resistance gene Radv was also mapped to LG 13 but at a further distance to the R4 locus, indicating that the Radv gene is different from the R4 gene. The tightly linked markers to the R4 gene will facilitate gene pyramiding in rust resistance breeding of sunflower.

Technical Abstract: 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 were genetically mapped. The rust resistance gene R4 in the germplasm line HA-R3 was derived from an Argentina 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 other rust resistance genes. 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 a total of 99.5 cM in length including 21 markers and averaging 4.7 cM per marker. Two markers, ZVG61 and ORS581, flanked the R4 gene at 1.6 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 with 11.3 cM from the R4 locus, indicating that Radv is not an allele of R4 locus. The markers tightly linked to the R4 gene will facilitate gene pyramiding for rust resistance breeding of sunflower.