Manipulation of ploidy for blueberry breeding: in vitro chromosome doubling of diploid Vaccinium duclouxii (Lévl.) Hand.-Mazz by trifluralin

The diversification, evolution, domestication, and breeding of many plant species have all been greatly aided by polyploidization. In this study, we reported a successful induction of autotetraploids of Vaccinium duclouxii (Lévl.) Hand.-Mazz, which was an important germplasm for developing highbush blueberry cultivars. The isolated stems of V. duclouxii were soaked in different concentrations of trifluralin solution, and then the ploidy of the seedlings sprouted from stems were identified by flow cytometry and chromosome counting analyses. The optimal condition for inducing tetraploid of V. duclouxii leaf bud was 0.002 % trifluralin for 48 h, which the induction rate reached 8.33 %. The morphological and anatomical characteristics of induced tetraploid seedlings were significantly different from those of the original diploid plants. The average stem diameter, leaf length, leaf width, and leaf thickness of the tetraploid plants showed significantly larger and thicker compared with the diploid progenitor plants. The stomata number of lower epidermis on the tetraploid seedling leaves only was 64.20 % of the diploid progenitors', while the average stomatal area was increased by 166.67 %. In addition, the length and width of guard cells were 128.57 % and 141.18 % of its diploid progenitor, separatively, and the chloroplast numbers were in guard cells increased by 157.36 %. The main leaf vein diameter, the upper epidermal thickness, palisade tissue and sponge tissue of induced tetraploid leaves were all significantly increased in comparison to its diploid progenitor, indicating that these indexes can be used for screening tetraploid seedlings during breeding program.