In vitro induction of allohexaploid and resulting phenotypic variation in Populus

Although triploid Populus varieties have been used widely in timber and pulpwood production, the performance of economic traits in Populus with higher ploidy levels remains unknown due to a lack of germplasms with higher ploidy. In this study, we first successfully induced hexaploids in Populus by treating triploid leaf explants with colchicine in vitro. In total, 32 hexaploids were produced. The frequency of hexaploids was significantly affected by the interaction between colchicine concentration and exposure time. The highest hexaploid induction efficiency was 16.89% (± 2.26), which was achieved by treating explants with 0.04% colchicine for 7 days. Compared to triploids, hexaploids had thinner epidermal hair, larger stomata and protoplasts, and fewer chloroplasts, indicating that significant phenotypic changes accompanied an increase in ploidy level. These hexaploids are valuable for investigating the performance of economic traits in Populus with higher ploidy levels and have the potential to be used as parents to produce new tetraploid and pentaploid germplasms in Populus breeding programs.