Abstract
Chromosome doubling is considered an important technique in poplar breeding, with many triploid clones being artificially induced and selected for promotion in the north and northeast of China because of their outstanding traits in vegetative growth and environmental adaption. In this study, the triploid yield of Populus simonii Carr × P. nigra var. italica (Moench.) Kochne was 23.41%, which exceeded the yield attained in our previous studies due to the use of an optimized method of chromosome doubling in the embryo sac at a high temperature. The development of the embryo sac after the pollination of this hybrid was investigated to determine the induction period. Ploidy of seedlings was identified by flow cytometry after initial filtering using the chloroplast counting method. Eleven triploids and one tetraploid were ultimately obtained, and the optimal operating conditions were exposure of female catkins to 41 °C for 2 h at 66 h after pollination (HAP). This study identified an efficient method of chromosome doubling in P. simonii × P. nigra var. italica and provided several polyploids for Populus polyploid breeding programs and subsequent studies.
Highlights
The induction of chromosome doubling during hybridization is an important strategy in the polyploid breeding of Populus
The developmental model of an embryo sac in P. simonii × P. nigra var. italica was classified as the Polygonum type, which could be divided into two stages: megasporogenesis and megagametogenesis
With maturation of the functional megaspore, the volume of the cell increased, and a vacuole was present, indicating the beginning of the embryo sac developmental stage (Fig. 2). The megaspore in this stage underwent three mitoses, which were targeted for chromosome doubling at a high temperature and formed an embryo sac with seven cells and eight nuclei
Summary
In P. adenopoda, female gametes were treated with high temperature during the megasporogenesis and embryo sac stages, and the triploid induction rates were 40 and 83.3%, respectively[9]. In P. alba × P. glandulosa, the highest efficiency of triploid induction was 87.0% for the embryo sac[11] These studies obtained higher induction rates than did previous studies using male gametes. During the embryo sac developmental stage, P. pseudo-simonii × P. nigra ‘Zheyin’ was treated with high temperature, and the triploid induction rate was 40%12. The pollen donor (P. simonii × (P. pyramidalis + Salix matsudana) clone) was selected due to its hybridization compatibility with the female parent[14], complementary advantages in growth vigour, and its straight stem. A high-temperature induction treatment applied after pollination was studied for the cross-combination P. simonii × P. nigra var. We obtained a certain amount of polyploidy seedlings and optimized the high-temperature induction treatment conditions according to the statistical analysis of an orthogonal experimental design after a preliminary experiment to assess tolerance to high temperatures
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