Overview of haploid technologies and opportunities in plant breeding

Haploid breeding technology serves as a pivotal approach to accelerate plant breeding by enabling the generation of homozygous doubled haploid (DH) lines within a single generation, thereby significantly shortening breeding cycles. We systematically categorize current haploid induction strategies into pollen-mediated, egg cell-mediated, and centromere-mediated approaches, based on their underlying mechanisms. Pollen-related approaches include in vitro microspore/anther culture, pollen treatment combined with embryo rescue, and mutations in genes regulating pollen development. Egg cell-related strategies encompass in vitro female gametophyte culture, mutations in genes involved in egg cell development, and the induction of parthenogenesis. Centromere-related techniques primarily achieve selective chromosome elimination through the manipulation of CENH3 and its associated factors, leading to haploid formation. We also highlight recent advances in haploid screening and chromosome doubling methods, along with the integration of gene editing and haploid induction technologies. These combined methods have facilitated the generation of edited lines in any genetic background (HI-Edit/IMGE), the development of cytoplasmic male sterile lines in diverse backgrounds, the sustainable reproduction and utilization of elite hybrid genotypes (reverse breeding), and the fixation of heterosis through clonal reproduction (synthetic apomixis). Haploid induction technology is becoming a cornerstone in the development of precise genetic improvement systems that are deeply integrated with modern breeding, making it possible to provide robust support for crop molecular design breeding.