Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/10/2008
Publication Date: 4/4/2008
Citation: Rojas-Barros, P., Hu, J., Jan, C.C. 2008. Molecular mapping of an apical branching gene of cultivated sunflower (Helianthus annuus L.). Theoretical and Applied Genetics. 117:19-28. Interpretive Summary: The commercial hybrids are produced by crossing a male-sterile inbred line (A-line) with a restorer male-fertile line (R-line). Branching of R lines extends pollen shed period, facilitating synchronized flowering with female lines in hybrid seed production fields. The development of new R-lines requires the incorporation of the recessive branching trait, which is laborious and time-consuming. The recessive gene b1 for apical branching has been widely used in the production of hybrid seed. Molecular markers tightly linked to the recessive b1 gene have been developed. These markers will effectively assist breeders to identify heterozygous nonbranched plants and facilitate the development of restorer lines.
Technical Abstract: Commercial hybrids of cultivated sunflower (Helianthus annuus L.) are obtained by crossing a cytoplasmic male-sterile line (A-line) with a restorer pollinator (R-line). The incorporation of a recessive branching trait to extend the pollination period of R-lines during hybrid seed production is laborious and time-consuming. By using target region polymorphism (TRAP) and bulked segregant analysis (BSA), we identified 15 TRAP markers linked to the b1 (branching) locus in a population of 229 F2 plants derived from a cross between nonbranched (HA 234) and branched (RHA 271) lines. TBr4-720 and TBr8-555 markers were linked to the b1 gene in the coupling phase at 0.5 cM (0.004 recombination frequency). The Tbr20-297 and Tbr20-494 markers flanked the b1 locus in the repulsion phase at genetic distances of 7.5 and 2.5 cM, respectively. Tbr19-395, also in the repulsion phase, mapped at 3.8 cM from the b1 locus and on the opposite side of the marker Tbr20-297. The 8A1 and 15B3 restriction fragment length polymorphic (RFLP) markers of linkage group (LG) 16 of the RHA 271 x HA 234 cultivated sunflower map anchored the b1 LG onto the RFLP map. Polymerase chain reaction (PCR)-based markers tightly linked to the recessive b1 gene have been developed. Their identification and the incorporation of the LG containing the b1 locus onto an RFLP map will be useful for marker-assisted selection (MAS) in breeding programs and provide the bases for map-based cloning of this gene.