Production of doubled haploids in wheat (Triticum aestivum L.) through microspore embryogenesis triggered by inducer chemicals

Abstract

Production of doubled haploids (DH) from microspores by androgenesis is a proven method to obtain homozygous individuals in a single step, thus the method is very useful in plant breeding. Since homozygosity is achieved in one generation, the breeder can avoid the numerous cycles of inbreeding required by conventional breeding systems and at the same time substantially reduce the population sizes required for effective selection of superior trait combinations. An efficient doubled haploid production system is also a preferred technique to produce homozygous transgenic plants. Dominant or recessive target gene(s) to be incorporated into gametic cells by genetic transformation can be fixed in homozygous form in a single generation. Doubled haploids are also important tools in plant genome mapping and studies of embryogenesis. In this chapter, there are described two unique and efficient systems — “flask” and “fresh microspore” systems for the production of doubled haploids, effective for a wide spectrum of genotypes in common wheat (Triticum aestivum L.). These systems rely upon three key steps. First, the microspores are switched from their naturally programmed pathway for gametophytic development (Fig. 2.13-la) to sporophytic development (Fig. 2.13-1b) by an inducer chemical treatment under proper physical conditions. Second, optimal culture conditions are provided, which include adequate nutrition and a favorable physical environment to help microspores elaborate their altered developmental programme leading to embryoid production, once a large population of reprogrammed microspores is obtained. Third, embryoids are germinated on solid, hormone-free medium to form doubled haploid plants. Cell divisions in treated microspores follow a well-organized and predictable pattern that leads to the formation of true “embryoids” rather than calli, ensuring success in plant regeneration. Cell divisions within the first 7 days in culture lead to the formation of a clearly defined multi-cellular structure, whose size is only 10–15 µm (diameter) larger than a microspore (Fig. 2.13-5a).