Fine mapping of open-bud duplicate genes in homoelogous chromosomes of tetraploid cotton

The open-bud mutant plant has a flower bud that is open at its tip due to the shortening of the corollas, resulting in exposure of the stigma and upper anthers. This mutant plant is potentially useful as a parent for producing hybrid cotton seeds. We have identified the open-bud trait to be inherited as recessive duplicate genes and finely mapped them in the homoelogous chromosome (chr) pair of chr. 18 (D13) and 13 (A13). Gossypium hirsutum substitution line 18, which has chr. 18 replaced by its corresponding homozygous chromosome in G. barbadense acc. 3-79 and the genotyped open-bud duplicate genes ob ₁ ob ₁ ob ₂ ob ₂, was crossed with the monomeric genotypic G. hirsutum acc. TM-1 and G. barbadense acc. 3-79 to produce two mapping populations. We then fine-mapped the duplicate open-bud gene ob ₁ in the chr. 18 (D13) and ob ₂ in the chr. 13 (A13) homoelogous chromosome pair in tetraploid cotton. Molecular markers closely linked with ob ₁ and ob ₂ will be useful tools in the development of open-bud lines by marker-assisted selection.