Abstract
Haploid induction (HI), an indispensable procedure in doubled haploid breeding, has attracted increasing attention in crop genetic improvement due to its ability to rapidly fix desirable traits in a homozygous state, thereby shortening the breeding cycle. However, HI has only been successfully implemented in a limited number of crops, and its underlying mechanisms remain largely enigmatic. This review summarizes five potential HI routes based on previous findings and the key events during the process of double fertilization in flowering plants. Among these HI methods, we suggest that sperm DNA fragmentation and ectopic expression of embryogenesis activator, as straightforward avenues for discovering new HI-related genes. We also emphasize that the combination of genome editing techniques with HI is a promising strategy to accelerate crop improvement and doubled haploid breeding. We envision that the proposed directions can pave the way for improving and deepening our understanding of HI mechanisms.