Double haploids are useful because they are:
Doubled haploid lines are produced from haploid plants by chromosome doubling, resulting in individuals where both chromosome sets are identical copies, achieving immediate complete homozygosity at every locus without residual heterozygosity or segregation. Genotypic value is fully fixed, allelic pairs AA or aa across genome, eliminating segregation in progeny and exposing recessive alleles. This purity is valuable because phenotype directly reflects genotype, dominance effects removed, deleterious recessives exposed for purging, and additive variance accurately estimated without dominance noise. Lines breed true instantly, uniformity essential for hybrid parent development and QTL mapping because background noise from heterozygosity disappears. Compared to conventional inbreeding requiring six to eight generations of selfing to reach 99% homozygosity, DH bypasses this lengthy process, accelerates varietal development, prevents inbreeding depression buildup, and provides immortal homozygous resource for genomics, marker-assisted selection, and seed industry maintenance of inbred lines for hybrids. In many vegetables, DH lines serve as parents for F1 hybrids producing uniform marketable product with heterosis; production protocols include microspore embryogenesis induced by heat stress, colchicine doubling during culture, and direct regeneration bypassing callus phase to minimize albinism and somaclonal variation risks in commercial application.
Ref: Forster BP et al. 2007 – DH advantages. Germanà MA. Haploids and doubled haploids in crop improvement