In vitro induction and identification of tetraploid plants of Paulownia tomentosa

Polyploidization is a major trend in plant evolution that has many advantages over diploid. In particular, the enlargement and lower fertility of polyploids are very attractive traits in forest tree breeding programs. We report here a system for the in vitro induction and identification of tetraploid plants of Paulownia tomentosa induced by colchicine treatment. Embryonic calluses derived from placentas were transferred to liquid Murashige and Skoog (MS) medium containing different concentrations of colchicine (0.01, 0.05, or 0.1%) and incubated for 24, 48, or 72 h on an orbital shaker at 110 rpm. The best result in terms of the production of tetraploid plantlets was obtained in the 48 h + 0.05% colchicine treatment, with more than 100 tetraploid plantlets being produced. The ploidy level of plantlets was verified by chromosome counts, flow cytometry, and morphology. The chromosome number of tetraploids was 2n = 4x = 80 and that of diploid plantlets was 2n = 2x = 40. The relative fluorescence intensity of tetraploids was twofold higher than that of diploids. The tetraploid and diploid plantlets differed significantly in leaf shape, with those of the former being round and those of the latter pentagonal. The mean length of the stomata was longer in tetraploid plants than diploid plants, and stomatal frequency was reduced with the increased ploidy level. The tetraploids had large floral organs that were easily distinguishable from those of diploid plants.