New insight into the mechanism of heterofertilization during maize haploid induction

To study the influence of both pollen competition ability (PCA) and haploid induction rate (HIR) on heterofertilization, we used maize haploid inducers with different HIRs as male parents. For these experiments, maize plants underwent dual pollination, first by the inducers and then by self-pollination at different time intervals. We found that PCA strongly influenced heterofertilization, as measured by the resulting ratio of hybrid kernels to selfed kernels. When log10 (hybrid kernel/selfed kernel) was close to 0, i.e., when pollen from the different parents arrived at the embryo sac nearly simultaneously, the heterofertilization rate (HFR) was high. Haploid inducers with a high HIR, such as CAU5 and CAUB73, led to not only more haploids and embryo aborted kernels but also more heterofertilized kernels, as compared with a non-inducer or with a haploid inducer with a low HIR. We thus conclude that PCA is an important factor that affects HFR through polytubey. In addition, during maize haploid induction, abnormal fertilization could also contribute to heterofertilization, which may be due to fertilization recovery of kernels that otherwise would have been aborted at early stage.