Reflections on doubled haploids in plant breeding

Abstract

Doubled haploid breeding has intrigued plant breeders for the past thirty years. The breeding method involves: 1. making haploid tissues or plants (1n) from heterozygous parents, and 2. doubling the chromosomes in the tissues (followed by regenerating plants) or plants to obtain diploid plants (2n) which are referred to as doubled haploids. At the haploid level, every gene is hemizygous. After chromosome doubling, which in theory makes an identical copy of each haploid chromosome, every gene is homozygous. Hence, the doubled haploid plant is completely homozygous. Occasionally doubled haploid plants have also been referred to as dihaploid plants, however, the classical definition of dihaploid is the haploid plant (1n = 2x) of an autotetraploid (2n = 4x). To avoid confusion, doubled haploid is preferred to dihaploid.