Early spontaneous diploidization of maternal maize haploids generated by in vivo haploid induction

The production of doubled haploid (DH) lines has become a key technology in maize (Zea mays L.) research and breeding. However, most of the haploid plants are sterile and in many cases artificial chromosome doubling involves the use of costly and toxic chemicals. Here, we report a special kind of doubled haploid named the early doubled haploid (EH) that was generated directly by in vivo haploid induction. We found 83 EH plants induced from the hybrid Zhengdan958, 55 families of its F_2:3 population and the parental lines, all of which were confirmed to be homozygous diploids via flow cytometry and 104 SSR markers. The progeny of EH₀ (EH₁) behaved in the same manner and showed the same potentialities as the parents of Zheng58 and Chang7-2. EH plants were also detected in other genetic backgrounds at a frequency of 1–3.5 % based on the total number of haploid plants. Because the EH lines exhibited completely fertility and were obtained from induction directly in one step, they could be used in DH breeding as a new breeding strategy. According to our observations, it is likely that spontaneous doubling in EH occurred during embryo development when haploid induction. The possible mechanism of EH is also discussed.