Haploidy in cultivated wheats: induction and utility in basic and applied research
The usefulness of haploid plants in basic research in cytogenetics, genetics, evolution, and practical plant breeding is well known. Haploid plants provide an efficient research tool for studies on induced mutagenesis and genetic transformation. They also help elucidate the genetic control of chromosome pairing inherently present in allopolyploids such as bread wheat, durum wheat, and oats. Genetic control of chromosome pairing in haploid nuclei has helped in assessing intergenomic relationships. By analyzing the degree and specificity of chromosome pairing in the Ph1- and ph1b-euhaploids (2n = 3x = 21; ABD), we demonstrated that the A and D genomes of wheat are more closely related to each other than either one is to the B genome. It is significant that the totipotent nature of a haploid cell is being exploited in several facets of biological research. In addition to its numerous applications in basic research, the haploidy approach provides an efficient means of producing truly homozygous lines, thereby accelerating the breeding process. Wheat cultivars developed from doubled haploids (DHs) have been released for cultivation in Canada, China, Europe, and Brazil. General characteristics and classification of haploids derived from diploid and polyploid species are provided in this article. Methods of extracting haploids of polyploid wheats are described, and applications of haploidy in basic and applied research are discussed.