Doubled Haploid Platform: An Accelerated Breeding Approach for Crop Improvement

Haploid plants provide an excellent example of cellular totipotency as they develop from either the male or female gametes without fertilization. Haploids can be induced in vivo and in vitro. Androgenesis is the development of haploids from male gametes. The two main techniques that are employed to generate androgenic plants in vitro are (a) anther culture and (b) microspore culture. The application of anther culture is widespread. Different developmental pathways of microspore embryogenesis have been reported in different plant species and in response to different stress treatments and its microspore developmental stage. Genotype or physiology of the donor plant, microspore developmental stage, stress pretreatment, culture medium and culture conditions affect the androgenesis process. Each crop has individual optimal pretreatment regimes and in vitro culture requirements. In vivo haploid induction techniques involve parthenogenesis and wide hybridization followed by chromosome elimination. In maize (Zea mays L.), haploids are commonly produced by in vivo haploid induction system and the method has been commercially exploited by both public and private sector organizations. Wide hybridization method is limited to potato and cereals. Wheat, barley and potato are excellent examples of wide hybridization followed by chromosome elimination system of haploid induction. The regenerated plants particularly in androgenesis need ploidy analysis to distinguish haploids from non-haploid plants. Regardless of the mode of development, doubling of haploid plants either spontaneously or by chemical means leads to a homozygous doubled haploid (DH) individual with two identical copies of each chromosome. Doubled haploids have been used in breeding programmes to produce homozygous genotypes in a number of important species and the number is increasing. DH populations are ideal for genetic mapping and allow the development of high-density marker maps that can then be exploited in quantitative trait locus identification. Genetic mapping using DHs had an impact in locating gene control traits for yield, quality, agronomy, abiotic and biotic stress. DHs now feature in cultivar production in a number of crops, and breeding time is considerably reduced. Hence, worldwide use of DH technology as an accelerated approach to crop improvement has become routine by many breeding companies and laboratories leading to the development of almost 300 new varieties.