An analysis of the use of haploidy in wheat improvement
2000
Mujeeb-Kazi, A. (Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT), Mexico, DF (Mexico))
Poly haploid production in wheat has relied heavily on anther culture and sexual crosses with Hordeum bulbosum. The occurrence of somaclonal variation, aneuploidy and genotypic specificity are major limitations of anther culture. The homoeologous group 5 crossability loci (Kr) influence the sexual crossings of wheat with H. bulbosum. Producing wheat haploids by sexual crosses of bread wheat x maize, pearl millet or Tripsacum has become a significant procedure since the production constraints of anther culture and H. bulbosum crosses are not present. Currently this procedure is being routinely used in wheat cytogenetics, wide crosses, wheat breeding, with extensions of the application into genetic engineering and molecular mapping. Recent technique advances in enhancing efficiency of haploid production utilize detached tillers from selected plants, their culture in a nutrient solution including sulfurous acid to avoid contamination, and hot water (43°C) immersion of the spikes for three minutes to effect emasculation. Hormonal treatment (2,4- dichlorophenoxy acetic acid,. 100 ppm) is essential, as is embryo rescue 14 days after pollination. The protocol is almost 100% effective for all bread wheat-cultivars. It has genotypic specificity for durums and TriticoSecale. The contribution of D genome chromosomes is a definitive factor in cross success. Mean frequencies of embryo excision are 25%, plantlet differentiation 80%, with a colchicine induced doubling range from 80 to 95%. Results of the techniques application in wide crosses, genetics, cytogenetics, breeding, and genetic transformation will be presented. Use of stored millet pollen to facilitate haploid production, due to unavailability of fresh pollen when wheat is grown, will be elucidated.
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