Embryo sac chromosome doubling in Populus alba × P. glandulosa induced by high temperature exposure to produce triploids

To determine the effects of the hours after pollination and the treatment durations on triploid production and reveal the effective stages of embryo sac chromosome doubling by high temperature exposure. At least three catkins were sampled, and 80 ovules were used for the determination of the embryo sac developmental process. Catkins (2-74 h after pollination) were treated to induce embryo sac chromosome doubling. Cytological observations revealed that the embryo sac development was a consecutive and asynchronous process. Fertilization occurred 50 h after pollination. In the offspring seedlings, 167 triploids were detected and the highest efficiency of triploid production was 87.0%. Among all the induced triploids, the most effective treatment period of inducing embryo sac chromosome doubling is from 26 to 50 h after pollination, and 121 triploids were obtained, representing 72.46% of the sum of all triploids. GLM-Univariate analysis indicated significant differences among the hours after pollination (F = 4.516, p = 0.045). However, the differences between the treatment durations (F = 0.077, p = 0.791) were not significant. Correlation analysis between the proportion of each embryo sac's developmental stage and the percentage of triploid production indicated that the third mitotic division may be the most effective stage for 2n female gamete induction.