Instant generation of four-parent derived autotetraploid rice through an in vitro fertilisation system

Hybridisation and polyploidisation are the pillars of crop improvement through breeding. Hybridisation combines genomes derived from genetically distinct parents, potentially eliciting heterosis, whereby the F1 progeny outperforms its parents in traits such as yield, biomass, and stress tolerance1. Polyploids are formed through autopolyploidisation, with autonomous genome doubling, or through allopolyploidisation following hybridisation across species2,3. Autopolyploids often exhibit enlarged organs, enhanced environmental tolerance, and elevated levels of bioactive compounds4–7; however, their fertility is generally reduced. Here, we employed a plant in vitro fertilisation (IVF) system that enables flexible fusion of isolated gametes8 to generate autotetraploid rice that inherits four parental genomes in equal amounts, herein termed “polyparental hybrids”. The hybrids exhibited enhanced vegetative growth, outperformed all parents in reproductive traits, and exhibited high fertility. This demonstrates that IVF-based autopolyploidisation involving multiple parents is a powerful breeding strategy that combines the advantages of hybridisation and polyploidy, with potential applicability across diverse flowering plants.