In vitro fertilization (IVF): production of distant hybrids with suitable genome combination

Hybridization generates biodiversity and wide hybridization plays a pivotal role in enhancing and broadening the useful attributes of crops. Hybridization can be achieved through sexual or somatic hybridization between distant species; however, sexual hybridization between intergeneric or inter-subfamily combinations often results in unsuccessful fertilization/embryogenesis due to pre- and/or post-fertilization barriers. In addition, as cytoplasmic organelles are maternally transmitted to the zygote via sexual reproduction, cytoplasmic genome hybridization is rare. Although somatic hybridization offers distinct advantages over sexual hybridization, the isolation and culture of protoplasts are not feasible in most plant species, including vital crops. Recently, allopolyploid wheat-rice or wheat-maize hybrid zygotes were produced by in vitro fertilization (IVF) using isolated wheat, rice, and maize gametes, and these hybrid zygotes developed into wheat cytoplasmic hybrids (cybrids) with wheat-rice or wheat-maize hybrid mitochondria. These indicate that the IVF system with isolated gametes provides a solution to limitations of fertilization barriers and one-way cytoplasmic inheritance in sexual and somatic hybridizations, and that the present rice-wheat cybrid, ^OryzaWheat, and maize-wheat, ^ZeaWheat, will provide a new horizon for the utilization of inter-subfamily genetic resources.