Submitted to: Proceedings Sunflower Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: 3/17/2005
Publication Date: 3/17/2005
Citation: Rojas-Barros, P., Jan, C.C., Hu, J. Mapping of a recessive branching gene in RHA 271 using molecular markers. Proceedings Sunflower Research Workshop. Available: http://www.sunflowernsa.com/research/research-workshop/documents/Rojas_MappingGene_05.pdf Interpretive Summary: The recessive gene b1 for apical branching is usually incorporated in restorer lines in sunflower to identify the hybrid plants during hybrid seed production. Molecular markers have not been reported for the recessive b1 allele, however they can be a very useful tool for identifying and incorporating the recessive b1 allele into restorer lines using marker-assisted selection (MAS). Efforts to map the b1 locus and to develop molecular markers for the recessive b1 allele for apical branching in sunflower are reported in the present study.
Technical Abstract: The Target Region Amplified Polymorphism (TRAP) technique is a powerful PCR-based system useful for generating polymorphic markers around targeted candidate gene sequence. Twenty-three fixed primers and 14 IR-dye arbitrary primers were assayed in a Bulked Segregant Analysis to identify TRAP markers associated with the recessive b1 gene for apical branching in sunflower. Seventeen fixed primers were selected from primers previously designed to map different branching genes, and six fixed primers were built either from branching gene sequences or based on an EST of sunflower homologue by BLAST searching to branching genes. Thirteen primer combinations were selected from the primer combinations founded to be polymorphic in the parents, non-branching line HA 231 and branching line RHA 271, and in the two F2 homozygous pools (branching and non-branching). These primers were used to analyze 116 F2 plants derived from the HA 231 x RHA 271 cross. The F2 population segregated 1:2:1 ratio (x2=3.93, p=0.14) for the recessive gene b1, and 20 TRAP loci were found tightly linked to the b1 locus. The linkage group covered a distance of 31.7 cM with an average distance of 1.5 cM. TBr4720 and TBr8555 TRAP markers cosegregated with the b1 locus, while TBr10366-TBr10440 and TBr13462 were flanking the b1 locus at a distance of 0.8 cM and 2.4 cM, respectively. All of them segregated in repulsion phase with the recessive b1 allele, and no special affinity was found between the branching genes from which one of the fixed primers were designed and the proximity to the locus b1 of the markers obtained. The closet markers in coupling phase with the recesive b1 allele were TBr8511-TBr12206 at 13.8 cM. The availability of these tightly linked molecular markers could be a starting point for map-based cloning of the b1 gene. New primer designed from the cosegregating TBr4720 and TBr8555 allele, will allow us to identify other markers useful for marker-assisted-selection of apical branching in sunflower.