A switch to haploid embryogenesis is controlled by the activity of histone deacetylases (HDACs). Blocking HDAC activity with HDAC inhibitors (HDACi), e.g. trichostatin A (TSA), in Brassica napus, B. rapa, B. oleracea, Arabidopsis thaliana and Capsicum annuum male gametophytes leads to a large increase in the proportion of cells that undergo embryogenic growth. In B. napus, treatment with one specific HDACi (SAHA) improves the conversion (i.e. germination) of these embryos into seedlings. Existing methods of culturing microspores of angiosperm plants following stress to produce haploid embryos, haploid plants and double haploid plants can be improved by adding HDACi to the culture medium. Advantageously, species hitherto recalcitrant to haploid embryogenesis via microspore culture are rendered useful when using HDACi. Haploid and double haploid plants are of industrial application in the plant breeding programmes.
