Efficient embryogenesis and regeneration in freshly isolated and cultured wheat (Triticum aestivum L.) microspores without stress pretreatment.
The major advantage of doubled haploids in plant breeding is the immediate achievement of complete homozygosity. Desired genotypes are thus fixed in one generation, reducing time and cost for cultivar or inbred development. Among the different technologies to produce doubled haploids, microspore embryogenesis is by far the most common. It usually requires reprogramming of microspores by stress such as cold, heat, and starvation, followed by embryo development under stress-free conditions. We report here the development of a simple and efficient isolated microspore culture system for producing doubled haploid wheat plants in a wide spectrum of genotypes, in which embryogenic microspores and embryos are formed without any apparent stress treatment. Microspores were isolated from fresh spikes in a nutrient-free medium by stirring and cultured in medium A2 in the dark at 25 degrees C. Once embryogenic microspores were formed, ovaries and phytohormones were added directly to the cultures without changing the medium. The cultures were incubated in the dark at 25-27 degrees C until the formation of embryos and then the embryos were transferred to regeneration medium. The regeneration frequency and percentage of green plants increased significantly using this protocol compared to the shed microspore culture method.