Challenges and Limitations to the Use of Haploidy in Crop Improvement

Abstract

There have been a number of recent reviews on the uses of doubled haploids in plant improvement (Kao 1996; Kush and Virmani 1996; Pelletier 1998; Bohanec 2002). Consequently this chapter will concentrate on the limitations and potentials of haploids and doubled haploids in plant improvement while emphasizing the recent literature. There is an impressive list of plant species in which haploids and doubled haploids have been produced (Maluszynski et al. 1996, 2003). However, most of the published protocols are developed by genotype selection, manipulation of donor plant growth conditions and modifications to culture media composition and culture conditions. There have been attempts at understanding the fundamental basis for gametophyte to sporophyte transition and morphogenesis, but our knowledge of how the process is regulated is still fragmentary (Kyo et al. 2003). What are the signals, genes and gene products involved in this process? For this technology to be widely used in crop improvement, greater insight into the molecular and biochemical basis for induction of gametophyte embryogenesis must be achieved. There are a number of emerging crop species of medicinal, herbal and neutraceutical value where genetic improvement would benefit from doubled haploid technology. While an empirical approach to haploidy is still useful, a fundamental understanding of the process would be invaluable for the development of genotypes with reliable and diverse characteristics. Significant advances have been made in the use of doubled haploids in the improvement of some species, e.g. members of the Brassicaceae, Poaceae and Solanaceae. However, there has been little improvement in the recovery of doubled haploids from members of the Fabaceae. Soybean, Glycine max (L.) Merr.; in spite of its commercial importance, anther culture remains the only route to haploidy (Hu et al. 1996; Rodrigues et al. 2004). In all cases, haploids are produced at a frequency too low to be of value in a soybean breeding program.