Review of doubled haploid production in durum and common wheat through wheat x maize hybridization

Production of doubled haploids (DHs) is an important methodology to speed up the process of breeding and development of mapping populations in crops. The procedure for DH production includes two major steps: haploid induction and chromosome doubling. Chromosome doubling of haploid plants has been routinely performed using colchicine. However, success and efficiency of haploid induction play the decisive role in using the DH method to breed and develop mapping populations in many crop species. In durum and common wheat, haploids can be produced in vivo by chromosome elimination after wide hybridization or in vitro by androgenesis (anther and microspore culture). In recent years, wide hybridization between wheat and maize has become a main approach for haploid production in wheat. In this method, the maize chromosomes are completely eliminated during the early development of the hybrid seeds after wheat spikes were pollinated with maize pollen. Numerous wheat cultivars and mapping populations have been developed using wheat-maize hybridization. In this paper, we review the procedures of DH production of durum and common wheat via wide hybridization with maize, the factors which affect the efficiency of DH production, and the mechanism of selective elimination of the maize genome during the early development of the hybrid embryos. We also report a highly efficient protocol for DH production in durum and common wheat, which was established based on the optimal conditions for each of the factors that affect the efficiency of DH production. This protocol has been used to develop over 3,000 DH lines belonging to 12 large mapping populations in durum and common wheat in our wheat germplasm enhancement and durum breeding programs.