Molecular mapping of an apical branching gene of cultivated sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.)

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 b(1) (branching) locus in a population of 229 F(2) plants derived from a cross between nonbranched (HA 234) and branched (RHA 271) lines. TBr4-720 and TBr8-555 markers were linked to the b(1) gene in the coupling phase at 0.5 cM (0.004 recombination frequency). The Tbr20-297 and Tbr20-494 markers flanked the b(1) 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 b(1) 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 b(1) LG onto the RFLP map. Polymerase chain reaction (PCR)-based markers tightly linked to the recessive b(1) gene have been developed. Their identification and the incorporation of the LG containing the b(1) 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.