Haploid production by wide crossing was reported in barley (Kasha and Kao, 1970) and tobacco (Burk et al., 1979).
Haploid embryos are produced in vivo by parthenogenesis, pseudogamy, or chromosome elimination after wide crossing.
When N. africana is used to pollinate N. tabacum, 0.25 to 1.42 percent of the progeny survive and can readily be identified as either F1 hybrids or maternal haploids.
As the quantitative trait loci (QTL) effects are small and highly influenced by environmental factors, accurate phenotyping with replicated trials is needed.
This is possible with doubled haploidy organisms because of their true breeding nature and because they can conveniently be produced in large numbers.
[6] Chen et al. (1994) used marker assisted backcross conversion with doubled haploidy of BC1 individuals to select stripe rust resistant lines in barley.
BSA is dependent on accurate phenotyping and the DH population has particular advantage in that they are true breeding and can be tested repeatedly.
DH populations are commonly used in bulked segregant analysis, which is a popular method in marker assisted breeding.
Genetic maps are very important to understand the structure and organization of genomes from which evolution patterns and syntenic relationships between species can be deduced.
Map construction is relatively easy using a DH population derived from a hybrid of two homozygous parents as the expected segregation ratio is simple, i.e. 1:1.
DH populations played a major role in facilitating the generation of the molecular marker maps in eight crop species.
A small doubled haploid (DH) population was used to demonstrate that a dwarfing gene in barley is located chromosome 5H.
The relevance of DHs to plant breeding has increased markedly in recent years owing to the development of protocols for 25 species.
DHs are also being developed in the medicinal herb Valeriana officinalis to select lines with high pharmacological activity.
[15] The ability to produce homozygous lines after a single round recombination saves a lot of time for the plant breeders.
More specific benefits include the possibility of seed propagation as an alternative to vegetative multiplication in ornamentals, and in species such as trees in which long life cycles and inbreeding depression preclude traditional breeding methods, doubled haploidy provides new alternatives.
In haploids produced from anther culture, it is observed that some plants are aneuploids and some are mixed haploid-diploid types.
Another disadvantage associated with the double haploidy is the cost involved in establishing tissue culture and growth facilities.